chore

.gitignore

@@ -10,3 +10,4 @@ prof.json
 *.cpuprofile
 *.cpuprofile.gz
 *v8.log*
+callgrind.*

.lazy.lua

@@ -16,6 +16,9 @@ vim.lsp.config("rust_analyzer", {
   settings = {
     ["rust-analyzer"] = {
       cargo = {
+        features = {
+          "tailcall"
+        }
       }
     }
   }

Cargo.toml

@@ -1,9 +1,42 @@
 [workspace]
 resolver = "3"
 members = [
-    "fix",
+  "fix",
+  "fix-bytecode",
+  "fix-compiler",
+  "fix-error",
+  "fix-lang",
+  "fix-runtime",
+  "fix-vm",
 ]
 
+[workspace.dependencies]
+bumpalo = {
+  version = "3.20",
+  features = [
+    "allocator-api2",
+    "boxed",
+    "collections",
+  ]
+}
+ere = "0.2"
+ghost-cell = "0.2"
+hashbrown = "0.16"
+num_enum = "0.7.5"
+rnix = "0.14"
+rowan = "0.16"
+smallvec = { version = "1.15", features = ["const_generics", "const_new"] }
+string-interner = "0.19"
+
+[workspace.dependencies.gc-arena]
+git = "https://github.com/kyren/gc-arena"
+rev = "75671ae03f53718357b741ed4027560f14e90836"
+features = ["allocator-api2", "hashbrown", "smallvec"]
+
+[profile.lto]
+inherits = "release"
+lto = true
+
 [profile.profiling]
 inherits = "release"
 debug = true

Justfile

@@ -29,3 +29,8 @@
 [no-exit-message]
 @evalp expr:
   cargo run --release --features prof -- eval --expr '{{expr}}'
+
+[no-exit-message]
+[positional-arguments]
+@cg *args='':
+  valgrind --tool=callgrind --dump-instr=yes --collect-jumps=yes "$@"

biome.json

@@ -1,70 +0,0 @@
-{
-  "$schema": "https://biomejs.dev/schemas/2.3.14/schema.json",
-  "vcs": {
-    "enabled": true,
-    "clientKind": "git",
-    "useIgnoreFile": true
-  },
-  "files": {
-    "includes": ["**", "!!**/dist"]
-  },
-  "formatter": {
-    "enabled": true,
-    "formatWithErrors": true,
-    "attributePosition": "auto",
-    "indentStyle": "space",
-    "indentWidth": 2,
-    "lineWidth": 110,
-    "lineEnding": "lf"
-  },
-  "linter": {
-    "rules": {
-      "style": {
-        "useNamingConvention": {
-          "level": "warn",
-          "options": {
-            "strictCase": false,
-            "conventions": [
-              {
-                "selector": { "kind": "objectLiteralProperty" },
-                "formats": ["camelCase", "PascalCase", "CONSTANT_CASE"]
-              },
-              {
-                "selector": { "kind": "typeProperty" },
-                "formats": ["camelCase", "snake_case"]
-              }
-            ]
-          }
-        }
-      }
-    }
-  },
-  "overrides": [
-    {
-      "includes": ["**/global.d.ts"],
-      "linter": {
-        "rules": {
-          "style": {
-            "useNamingConvention": "off"
-          }
-        }
-      }
-    }
-  ],
-  "javascript": {
-    "formatter": {
-      "arrowParentheses": "always",
-      "bracketSameLine": false,
-      "bracketSpacing": true,
-      "jsxQuoteStyle": "double",
-      "quoteProperties": "asNeeded",
-      "semicolons": "always",
-      "trailingCommas": "all"
-    }
-  },
-  "json": {
-    "formatter": {
-      "trailingCommas": "none"
-    }
-  }
-}

fix-bytecode/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "fix-bytecode"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+colored = "3.1.1"
+num_enum = { workspace = true }
+string-interner = { workspace = true }
+
+fix-lang = { path = "../fix-lang" }

fix-bytecode/src/disassembler.rs

@@ -1,16 +1,15 @@
 use std::fmt::Write;
 
-use colored::Colorize;
+use colored::Colorize as _;
-use num_enum::TryFromPrimitive;
 
-use crate::codegen::{InstructionPtr, Op};
+use crate::{InstructionPtr, Op, OperandType, PrimOpPhase};
 
-pub(crate) trait DisassemblerContext {
+pub trait DisassemblerContext {
-    fn lookup_string(&self, id: u32) -> &str;
+    fn resolve_string(&self, id: u32) -> &str;
     fn get_code(&self) -> &[u8];
 }
 
-pub(crate) struct Disassembler<'a, Ctx> {
+pub struct Disassembler<'a, Ctx> {
     code: &'a [u8],
     ctx: &'a Ctx,
     pc: usize,
@@ -25,12 +24,14 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
         }
     }
 
+    #[inline(always)]
     fn read_u8(&mut self) -> u8 {
         let b = self.code[self.pc];
         self.pc += 1;
         b
     }
 
+    #[inline(always)]
     fn read_u16(&mut self) -> u16 {
         let bytes = self.code[self.pc..self.pc + 2]
             .try_into()
@@ -39,6 +40,7 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
         u16::from_le_bytes(bytes)
     }
 
+    #[inline(always)]
     fn read_u32(&mut self) -> u32 {
         let bytes = self.code[self.pc..self.pc + 4]
             .try_into()
@@ -47,6 +49,7 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
         u32::from_le_bytes(bytes)
     }
 
+    #[inline(always)]
     fn read_i32(&mut self) -> i32 {
         let bytes = self.code[self.pc..self.pc + 4]
             .try_into()
@@ -55,6 +58,7 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
         i32::from_le_bytes(bytes)
     }
 
+    #[inline(always)]
     fn read_i64(&mut self) -> i64 {
         let bytes = self.code[self.pc..self.pc + 8]
             .try_into()
@@ -63,6 +67,7 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
         i64::from_le_bytes(bytes)
     }
 
+    #[inline(always)]
     fn read_f64(&mut self) -> f64 {
         let bytes = self.code[self.pc..self.pc + 8]
             .try_into()
@@ -71,6 +76,36 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
         f64::from_le_bytes(bytes)
     }
 
+    #[inline(always)]
+    fn read_operand_data(&mut self) {
+        use OperandType::*;
+        let tag = self.read_u8();
+        let ty = OperandType::try_from(tag).expect("invalid operand type");
+        match ty {
+            Const => {
+                self.read_u32();
+            }
+            BigInt => {
+                self.read_i64();
+            }
+            Local => {
+                self.read_u8();
+                self.read_u32();
+            }
+            BuiltinConst => {
+                self.read_u32();
+            }
+            Builtins => {}
+            ReplBinding => {
+                self.read_u32();
+            }
+            ScopedImportBinding => {
+                self.read_u32();
+                self.read_u32();
+            }
+        }
+    }
+
     pub fn disassemble(&mut self) -> String {
         self.disassemble_impl(false)
     }
@@ -165,7 +200,7 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
     }
 
     fn decode_instruction(&mut self, op_byte: u8, current_pc: usize) -> (&'static str, String) {
-        let op = Op::try_from_primitive(op_byte).expect("invalid op code");
+        let op = Op::try_from(op_byte).expect("invalid op code");
 
         match op {
             Op::PushSmi => {
@@ -182,7 +217,7 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
             }
             Op::PushString => {
                 let idx = self.read_u32();
-                let s = self.ctx.lookup_string(idx);
+                let s = self.ctx.resolve_string(idx);
                 let len = s.len();
                 let mut s_fmt = format!("{:?}", s);
                 if s_fmt.len() > 60 {
@@ -238,11 +273,11 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
                 arg_str.push_str(" Args=[");
                 for _ in 0..req_count {
                     let idx = self.read_u32();
-                    arg_str.push_str(&format!("Req({}) ", self.ctx.lookup_string(idx)));
+                    arg_str.push_str(&format!("Req({}) ", self.ctx.resolve_string(idx)));
                 }
                 for _ in 0..opt_count {
                     let idx = self.read_u32();
-                    arg_str.push_str(&format!("Opt({}) ", self.ctx.lookup_string(idx)));
+                    arg_str.push_str(&format!("Opt({}) ", self.ctx.resolve_string(idx)));
                 }
 
                 let total_args = req_count + opt_count;
@@ -256,37 +291,93 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
             }
 
             Op::Call => {
-                let span_id = self.read_u32();
+                self.read_operand_data();
-                ("Call", format!("span={}", span_id))
+                ("Call", "arg=?".into())
+            }
+            Op::DispatchPrimOp => {
+                let phase = PrimOpPhase::try_from(self.read_u8()).expect("invalid primop phase");
+                ("DispatchPrimOp", format!("phase={phase:?}"))
             }
-            Op::CallNoSpan => ("CallNoSpan", String::new()),
 
             Op::MakeAttrs => {
-                let count = self.read_u32();
+                let static_count = self.read_u32();
-                ("MakeAttrs", format!("size={}", count))
+                let dynamic_count = self.read_u32();
+                let mut args = format!("static={} dynamic={}", static_count, dynamic_count);
+
+                for _ in 0..static_count {
+                    let key_id = self.read_u32();
+                    let _ = write!(args, " [{}={}", self.ctx.resolve_string(key_id), key_id);
+                    self.read_operand_data();
+                    let _span_id = self.read_u32();
+                    args.push(']');
+                }
+
+                for _ in 0..dynamic_count {
+                    let _ = write!(args, " [dyn");
+                    self.read_operand_data();
+                    let _span_id = self.read_u32();
+                    args.push(']');
+                }
+
+                ("MakeAttrs", args)
             }
             Op::MakeEmptyAttrs => ("MakeEmptyAttrs", String::new()),
 
-            Op::Select => {
+            Op::SelectStatic => {
-                let path_len = self.read_u16();
-                let span_id = self.read_u32();
-                ("Select", format!("path_len={} span={}", path_len, span_id))
-            }
-            Op::SelectDefault => {
-                let path_len = self.read_u16();
                 let span_id = self.read_u32();
+                let key_id = self.read_u32();
                 (
-                    "SelectDefault",
+                    "SelectStatic",
-                    format!("path_len={} span={}", path_len, span_id),
+                    format!("key={} span={}", self.ctx.resolve_string(key_id), span_id),
                 )
             }
-            Op::HasAttr => {
+            Op::SelectDynamic => {
-                let path_len = self.read_u16();
+                let span_id = self.read_u32();
-                ("HasAttr", format!("path_len={}", path_len))
+                ("SelectDynamic", format!("span={}", span_id))
+            }
+            Op::HasAttrPathStatic => {
+                let span_id = self.read_u32();
+                let key_id = self.read_u32();
+                (
+                    "HasAttrPathStatic",
+                    format!("key={} span={}", self.ctx.resolve_string(key_id), span_id),
+                )
+            }
+            Op::HasAttrPathDynamic => {
+                let span_id = self.read_u32();
+                ("HasAttrPathDynamic", format!("span={}", span_id))
+            }
+            Op::HasAttrStatic => {
+                let key_id = self.read_u32();
+                (
+                    "HasAttrStatic",
+                    format!("key={}", self.ctx.resolve_string(key_id)),
+                )
+            }
+            Op::HasAttrDynamic => ("HasAttrDynamic", String::new()),
+            Op::HasAttrResolve => ("HasAttrResolve", String::new()),
+            Op::JumpIfSelectSucceeded => {
+                let offset = self.read_i32();
+                let target = (current_pc as isize + 1 + 4 + offset as isize) as usize;
+                (
+                    "JumpIfSelectSucceeded",
+                    format!("-> {:04x} offset={}", target, offset),
+                )
+            }
+            Op::JumpIfSelectFailed => {
+                let offset = self.read_i32();
+                let target = (current_pc as isize + 1 + 4 + offset as isize) as usize;
+                (
+                    "JumpIfSelectFailed",
+                    format!("-> {:04x} offset={}", target, offset),
+                )
             }
 
             Op::MakeList => {
                 let count = self.read_u32();
+                for _ in 0..count {
+                    self.read_operand_data();
+                }
                 ("MakeList", format!("size={}", count))
             }
             Op::MakeEmptyList => ("MakeEmptyList", String::new()),
@@ -330,18 +421,25 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
                 let force = self.read_u8();
                 ("ConcatStrings", format!("count={} force={}", count, force))
             }
-            Op::ResolvePath => ("ResolvePath", String::new()),
+            Op::CoerceToString => ("CoerceToString", String::new()),
+            Op::ResolvePath => {
+                let dir_id = self.read_u32();
+                let dir = self.ctx.resolve_string(dir_id);
+                ("ResolvePath", format!("dir={:?}", dir))
+            }
             Op::Assert => {
                 let raw_idx = self.read_u32();
                 let span_id = self.read_u32();
                 ("Assert", format!("text_id={} span={}", raw_idx, span_id))
             }
-            Op::PushWith => ("PushWith", String::new()),
+            Op::LookupWith => {
-            Op::PopWith => ("PopWith", String::new()),
-            Op::WithLookup => {
                 let idx = self.read_u32();
-                let name = self.ctx.lookup_string(idx);
+                let name = self.ctx.resolve_string(idx);
-                ("WithLookup", format!("{:?}", name))
+                let n = self.read_u8();
+                for _ in 0..n {
+                    self.read_operand_data();
+                }
+                ("LookupWith", format!("sym={:?} n={}", name, n))
             }
 
             Op::LoadBuiltins => ("LoadBuiltins", String::new()),
@@ -349,21 +447,19 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
                 let id = self.read_u8();
                 ("LoadBuiltin", format!("id={}", id))
             }
-            Op::MkPos => {
-                let span_id = self.read_u32();
-                ("MkPos", format!("id={}", span_id))
-            }
             Op::LoadReplBinding => {
                 let idx = self.read_u32();
-                let name = self.ctx.lookup_string(idx);
+                let name = self.ctx.resolve_string(idx);
                 ("LoadReplBinding", format!("{:?}", name))
             }
             Op::LoadScopedBinding => {
+                let slot = self.read_u32();
                 let idx = self.read_u32();
-                let name = self.ctx.lookup_string(idx);
+                let name = self.ctx.resolve_string(idx);
-                ("LoadScopedBinding", format!("{:?}", name))
+                ("LoadScopedBinding", format!("slot={} {:?}", slot, name))
             }
             Op::Return => ("Return", String::new()),
+            Op::Illegal => ("Illegal", String::new()),
         }
     }
 }

fix-bytecode/src/lib.rs

@@ -0,0 +1,532 @@
+#![allow(dead_code)]
+
+use fix_lang::{BuiltinId, StringId};
+use num_enum::TryFromPrimitive;
+use string_interner::Symbol as _;
+
+pub mod disassembler;
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct InstructionPtr(pub usize);
+
+#[repr(u8)]
+#[derive(Debug, Clone, Copy, TryFromPrimitive)]
+#[allow(clippy::enum_variant_names)]
+pub enum Op {
+    PushSmi,
+    PushBigInt,
+    PushFloat,
+    PushString,
+    PushNull,
+    PushTrue,
+    PushFalse,
+
+    LoadLocal,
+    LoadOuter,
+    StoreLocal,
+    AllocLocals,
+
+    MakeThunk,
+    MakeClosure,
+    MakePatternClosure,
+
+    Call,
+    DispatchPrimOp,
+
+    MakeAttrs,
+    MakeEmptyAttrs,
+    SelectStatic,
+    SelectDynamic,
+    HasAttrPathStatic,
+    HasAttrPathDynamic,
+    HasAttrStatic,
+    HasAttrDynamic,
+    HasAttrResolve,
+    JumpIfSelectSucceeded,
+    JumpIfSelectFailed,
+
+    MakeList,
+    MakeEmptyList,
+
+    OpAdd,
+    OpSub,
+    OpMul,
+    OpDiv,
+    OpEq,
+    OpNeq,
+    OpLt,
+    OpGt,
+    OpLeq,
+    OpGeq,
+    OpConcat,
+    OpUpdate,
+
+    OpNeg,
+    OpNot,
+
+    JumpIfFalse,
+    JumpIfTrue,
+    Jump,
+
+    CoerceToString,
+
+    ConcatStrings,
+    ResolvePath,
+
+    Assert,
+
+    LookupWith,
+
+    LoadBuiltins,
+    LoadBuiltin,
+
+    LoadReplBinding,
+    LoadScopedBinding,
+
+    Return,
+
+    Illegal,
+}
+
+#[repr(u8)]
+#[derive(Debug, Clone, Copy, TryFromPrimitive)]
+pub enum OperandType {
+    Const,
+    BigInt,
+    Local,
+    BuiltinConst,
+    Builtins,
+    ReplBinding,
+    ScopedImportBinding,
+}
+
+pub enum Const {
+    Smi(i32),
+    Float(f64),
+    Bool(bool),
+    String(StringId),
+    Path(StringId),
+    PrimOp {
+        id: BuiltinId,
+        arity: u8,
+        dispatch_ip: u32,
+    },
+    Null,
+}
+
+#[repr(u8)]
+#[derive(Debug, Clone, Copy, TryFromPrimitive)]
+pub enum AttrKeyType {
+    Static,
+    Dynamic,
+}
+
+pub enum OperandData {
+    Const(u32),
+    BigInt(i64),
+    Local { layer: u8, idx: u32 },
+    BuiltinConst(StringId),
+    Builtins,
+    ReplBinding(StringId),
+    ScopedImportBinding { slot_id: u32, name: StringId },
+}
+
+#[repr(u8)]
+#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
+pub enum PrimOpPhase {
+    Abort,
+    Add,
+    AddErrorContext,
+
+    All,
+    AllCallPred,
+    AllCheck,
+
+    Any,
+    AnyCallPred,
+    AnyCheck,
+
+    AppendContext,
+    AttrNames,
+    AttrValues,
+    BaseNameOf,
+    BitAnd,
+    BitOr,
+    BitXor,
+    Break,
+    CatAttrs,
+    Ceil,
+    CompareVersions,
+    ConcatLists,
+    ConcatMap,
+    ConcatStringsSep,
+    ConvertHash,
+
+    DeepSeq,
+    DeepSeqPush,
+    DeepSeqLoop,
+
+    Derivation,
+    DerivationStrict,
+    DirOf,
+    Div,
+    Elem,
+    ElemAt,
+    FetchGit,
+    FetchMercurial,
+    FetchTarball,
+    FetchTree,
+    FetchUrl,
+
+    FilterForceList,
+    FilterCallPred,
+    FilterCheck,
+
+    FilterSource,
+    FindFile,
+    Floor,
+    FoldlStrict,
+    FoldlStrictEmpty,
+    FoldlStrictCall1,
+    FoldlStrictCall2,
+    FoldlStrictUpdate,
+    FromJSON,
+    FromTOML,
+    FunctionArgs,
+    GenList,
+    GenericClosure,
+    GetAttr,
+    GetContext,
+    GetEnv,
+    GroupBy,
+    HasAttr,
+    HasContext,
+    HashFile,
+    HashString,
+    Head,
+    Import,
+    IntersectAttrs,
+    IsAttrs,
+    IsBool,
+    IsFloat,
+    IsFunction,
+    IsInt,
+    IsList,
+    IsNull,
+    IsPath,
+    IsString,
+    Length,
+    LessThan,
+    ListToAttrs,
+    Map,
+    MapAttrs,
+    Match,
+    Mul,
+    ParseDrvName,
+    Partition,
+    Path,
+    PathExists,
+    Placeholder,
+    ReadDir,
+    ReadFile,
+    ReadFileType,
+    RemoveAttrs,
+    ReplaceStrings,
+    ScopedImport,
+    Seq,
+    Sort,
+    Split,
+    SplitVersion,
+    StorePath,
+    StringLength,
+    Sub,
+    Substring,
+    Tail,
+    Throw,
+    ToFile,
+    ToJSON,
+    ToPath,
+    ToString,
+    ToXML,
+    Trace,
+    TryEval,
+    TypeOf,
+    UnsafeDiscardStringContext,
+    UnsafeGetAttrPos,
+    Warn,
+    ZipAttrsWith,
+
+    ForceResultShallow,
+    ForceResultShallowPush,
+    ForceResultShallowLoop,
+    ForceResultDeepFinish,
+
+    EqStep,
+    EqForce,
+
+    CallPattern,
+    CallFunctor1,
+    CallFunctor2,
+
+    ImportFinalize,
+    ScopedImportFinalize,
+
+    AppendContextLoop,
+    AppendContextEntryForced,
+    AppendContextOutputsForced,
+    AppendContextOutputElementLoop,
+    AppendContextOutputElementForced,
+
+    UnsafeDiscardOutputDependency,
+
+    Illegal,
+}
+
+impl TryFrom<u8> for PrimOpPhase {
+    type Error = u8;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        if (0..Self::Illegal as u8).contains(&value) {
+            Ok(unsafe { std::mem::transmute::<u8, Self>(value) })
+        } else {
+            Err(value)
+        }
+    }
+}
+
+impl PrimOpPhase {
+    pub fn entry_for_builtin(id: BuiltinId) -> Self {
+        use BuiltinId::*;
+        match id {
+            Abort => Self::Abort,
+            Add => Self::Add,
+            AddErrorContext => Self::AddErrorContext,
+            All => Self::All,
+            Any => Self::Any,
+            AppendContext => Self::AppendContext,
+            AttrNames => Self::AttrNames,
+            AttrValues => Self::AttrValues,
+            BaseNameOf => Self::BaseNameOf,
+            BitAnd => Self::BitAnd,
+            BitOr => Self::BitOr,
+            BitXor => Self::BitXor,
+            Break => Self::Break,
+            CatAttrs => Self::CatAttrs,
+            Ceil => Self::Ceil,
+            CompareVersions => Self::CompareVersions,
+            ConcatLists => Self::ConcatLists,
+            ConcatMap => Self::ConcatMap,
+            ConcatStringsSep => Self::ConcatStringsSep,
+            ConvertHash => Self::ConvertHash,
+            DeepSeq => Self::DeepSeq,
+            Derivation => Self::Derivation,
+            DerivationStrict => Self::DerivationStrict,
+            DirOf => Self::DirOf,
+            Div => Self::Div,
+            Elem => Self::Elem,
+            ElemAt => Self::ElemAt,
+            FetchGit => Self::FetchGit,
+            FetchMercurial => Self::FetchMercurial,
+            FetchTarball => Self::FetchTarball,
+            FetchTree => Self::FetchTree,
+            FetchUrl => Self::FetchUrl,
+            Filter => Self::FilterForceList,
+            FilterSource => Self::FilterSource,
+            FindFile => Self::FindFile,
+            Floor => Self::Floor,
+            FoldlStrict => Self::FoldlStrict,
+            FromJSON => Self::FromJSON,
+            FromTOML => Self::FromTOML,
+            FunctionArgs => Self::FunctionArgs,
+            GenList => Self::GenList,
+            GenericClosure => Self::GenericClosure,
+            GetAttr => Self::GetAttr,
+            GetContext => Self::GetContext,
+            GetEnv => Self::GetEnv,
+            GroupBy => Self::GroupBy,
+            HasAttr => Self::HasAttr,
+            HasContext => Self::HasContext,
+            HashFile => Self::HashFile,
+            HashString => Self::HashString,
+            Head => Self::Head,
+            Import => Self::Import,
+            IntersectAttrs => Self::IntersectAttrs,
+            IsAttrs => Self::IsAttrs,
+            IsBool => Self::IsBool,
+            IsFloat => Self::IsFloat,
+            IsFunction => Self::IsFunction,
+            IsInt => Self::IsInt,
+            IsList => Self::IsList,
+            IsNull => Self::IsNull,
+            IsPath => Self::IsPath,
+            IsString => Self::IsString,
+            Length => Self::Length,
+            LessThan => Self::LessThan,
+            ListToAttrs => Self::ListToAttrs,
+            Map => Self::Map,
+            MapAttrs => Self::MapAttrs,
+            Match => Self::Match,
+            Mul => Self::Mul,
+            ParseDrvName => Self::ParseDrvName,
+            Partition => Self::Partition,
+            Path => Self::Path,
+            PathExists => Self::PathExists,
+            Placeholder => Self::Placeholder,
+            ReadDir => Self::ReadDir,
+            ReadFile => Self::ReadFile,
+            ReadFileType => Self::ReadFileType,
+            RemoveAttrs => Self::RemoveAttrs,
+            ReplaceStrings => Self::ReplaceStrings,
+            ScopedImport => Self::ScopedImport,
+            Seq => Self::Seq,
+            Sort => Self::Sort,
+            Split => Self::Split,
+            SplitVersion => Self::SplitVersion,
+            StorePath => Self::StorePath,
+            StringLength => Self::StringLength,
+            Sub => Self::Sub,
+            Substring => Self::Substring,
+            Tail => Self::Tail,
+            Throw => Self::Throw,
+            ToFile => Self::ToFile,
+            ToJSON => Self::ToJSON,
+            ToPath => Self::ToPath,
+            ToString => Self::ToString,
+            ToXML => Self::ToXML,
+            Trace => Self::Trace,
+            TryEval => Self::TryEval,
+            TypeOf => Self::TypeOf,
+            UnsafeDiscardStringContext => Self::UnsafeDiscardStringContext,
+            UnsafeDiscardOutputDependency => Self::UnsafeDiscardOutputDependency,
+            UnsafeGetAttrPos => Self::UnsafeGetAttrPos,
+            Warn => Self::Warn,
+            ZipAttrsWith => Self::ZipAttrsWith,
+        }
+    }
+
+    pub fn ip(self) -> u32 {
+        self as u32 * 2
+    }
+}
+
+pub struct BytecodeReader<'a> {
+    bytecode: &'a [u8],
+    pc: usize,
+    inst_start_pc: usize,
+}
+
+impl<'a> BytecodeReader<'a> {
+    pub fn new(bytecode: &'a [u8], pc: usize) -> Self {
+        Self {
+            bytecode,
+            pc,
+            inst_start_pc: pc,
+        }
+    }
+
+    #[inline(always)]
+    pub fn from_after_op(bytecode: &'a [u8], inst_start_pc: usize) -> Self {
+        Self {
+            bytecode,
+            pc: inst_start_pc + 1,
+            inst_start_pc,
+        }
+    }
+
+    #[inline(always)]
+    #[cfg_attr(debug_assertions, track_caller)]
+    fn read_array<const N: usize>(&mut self) -> [u8; N] {
+        let ret = self.bytecode[self.pc..self.pc + N]
+            .try_into()
+            .expect("read_array failed");
+        self.pc += N;
+        ret
+    }
+
+    #[inline(always)]
+    pub fn read_op(&mut self) -> Op {
+        self.inst_start_pc = self.pc;
+        let byte = self.bytecode[self.pc];
+        if !(0..Op::Illegal as u8).contains(&byte) {
+            std::hint::cold_path();
+            panic!("unknown opcode: {byte:#04x}")
+        }
+        self.pc += 1;
+        unsafe { std::mem::transmute::<u8, Op>(byte) }
+    }
+
+    #[inline(always)]
+    pub fn read_u8(&mut self) -> u8 {
+        let val = self.bytecode[self.pc];
+        self.pc += 1;
+        val
+    }
+
+    #[inline(always)]
+    pub fn read_u16(&mut self) -> u16 {
+        u16::from_le_bytes(self.read_array())
+    }
+
+    #[inline(always)]
+    pub fn read_u32(&mut self) -> u32 {
+        u32::from_le_bytes(self.read_array())
+    }
+
+    #[inline(always)]
+    pub fn read_i32(&mut self) -> i32 {
+        i32::from_le_bytes(self.read_array())
+    }
+
+    #[inline(always)]
+    pub fn read_i64(&mut self) -> i64 {
+        i64::from_le_bytes(self.read_array())
+    }
+
+    #[inline(always)]
+    pub fn read_f64(&mut self) -> f64 {
+        f64::from_le_bytes(self.read_array())
+    }
+
+    #[inline(always)]
+    pub fn read_string_id(&mut self) -> StringId {
+        let raw = self.read_u32();
+        #[allow(clippy::unwrap_used)]
+        StringId(string_interner::symbol::SymbolU32::try_from_usize(raw as usize).unwrap())
+    }
+
+    #[inline(always)]
+    pub fn read_operand_data(&mut self) -> OperandData {
+        let tag = self.read_u8();
+        let Ok(ty) = OperandType::try_from_primitive(tag)
+            .map_err(|err| panic!("unknown operand tag: {:#04x}", err.number));
+        match ty {
+            OperandType::Const => OperandData::Const(self.read_u32()),
+            OperandType::BigInt => OperandData::BigInt(self.read_i64()),
+            OperandType::Local => {
+                let layer = self.read_u8();
+                let idx = self.read_u32();
+                OperandData::Local { layer, idx }
+            }
+            OperandType::BuiltinConst => OperandData::BuiltinConst(self.read_string_id()),
+            OperandType::Builtins => OperandData::Builtins,
+            OperandType::ReplBinding => OperandData::ReplBinding(self.read_string_id()),
+            OperandType::ScopedImportBinding => {
+                let slot_id = self.read_u32();
+                let name = self.read_string_id();
+                OperandData::ScopedImportBinding { slot_id, name }
+            }
+        }
+    }
+
+    pub fn pc(&self) -> usize {
+        self.pc
+    }
+
+    pub fn set_pc(&mut self, pc: usize) {
+        self.pc = pc;
+    }
+
+    pub fn inst_start_pc(&self) -> usize {
+        self.inst_start_pc
+    }
+}

fix-compiler/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "fix-compiler"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+bumpalo = { workspace = true }
+colored = "3.1.1"
+ghost-cell = { workspace = true }
+hashbrown = { workspace = true }
+rnix = { workspace = true }
+rowan = { workspace = true }
+string-interner = { workspace = true }
+
+fix-bytecode = { path = "../fix-bytecode" }
+fix-error = { path = "../fix-error" }
+fix-lang = { path = "../fix-lang" }
+fix-runtime = { path = "../fix-runtime" }
+tracing = "0.1"

fix-compiler/src/context.rs

@@ -0,0 +1,542 @@
+use bumpalo::Bump;
+use fix_bytecode::{Const, InstructionPtr, Op, PrimOpPhase};
+use fix_error::{Error, Result, Source};
+use fix_lang::{StringId, Symbol};
+use fix_runtime::{StaticValue, VmCode, VmRuntimeCtx};
+use ghost_cell::{GhostCell, GhostToken};
+use hashbrown::{HashMap, HashSet};
+use string_interner::DefaultStringInterner;
+
+use crate::BytecodeContext;
+use crate::ir::downgrade::{Downgrade as _, DowngradeContext};
+use crate::ir::{
+    GhostMaybeThunkRef, GhostRoIrRef, GhostRoMaybeThunkRef, GhostRoRef, Ir, MaybeThunk, RawIrRef,
+    ThunkId,
+};
+
+pub struct CodeState {
+    pub bytecode: Vec<u8>,
+    pub sources: Vec<Source>,
+    pub spans: Vec<(usize, rnix::TextRange)>,
+    pub thunk_count: usize,
+    pub global_env: HashMap<StringId, MaybeThunk>,
+}
+
+impl CodeState {
+    pub fn new(strings: &mut DefaultStringInterner) -> Self {
+        let global_env = crate::ir::new_global_env(strings);
+        let mut bytecode = Vec::with_capacity(PrimOpPhase::Illegal as usize * 2);
+        for phase in 0..=PrimOpPhase::Illegal as u8 {
+            bytecode.push(Op::DispatchPrimOp as u8);
+            bytecode.push(phase);
+        }
+        Self {
+            sources: Vec::new(),
+            spans: Vec::new(),
+            thunk_count: 0,
+            bytecode,
+            global_env,
+        }
+    }
+
+    pub fn compile_bytecode<'ctx>(
+        &'ctx mut self,
+        source: Source,
+        extra_scope: Option<ExtraScope<'ctx>>,
+        runtime: &'ctx mut impl VmRuntimeCtx,
+    ) -> Result<InstructionPtr> {
+        let mut compiler = CompilerCtx {
+            code: self,
+            runtime,
+        };
+        compiler.compile_bytecode(source, extra_scope)
+    }
+}
+
+impl VmCode for CodeState {
+    fn bytecode(&self) -> &[u8] {
+        &self.bytecode
+    }
+
+    fn compile_with_scope(
+        &mut self,
+        source: Source,
+        extra_scope: Option<fix_runtime::ExtraScope>,
+        runtime: &mut impl VmRuntimeCtx,
+    ) -> Result<InstructionPtr> {
+        let extra = extra_scope.map(|s| match s {
+            fix_runtime::ExtraScope::ScopedImport { keys, slot_id } => {
+                ExtraScope::ScopedImport { keys, slot_id }
+            }
+        });
+        CodeState::compile_bytecode(self, source, extra, runtime)
+    }
+}
+
+struct CompilerCtx<'a, R: VmRuntimeCtx> {
+    code: &'a mut CodeState,
+    runtime: &'a mut R,
+}
+
+impl<'a, R: VmRuntimeCtx> CompilerCtx<'a, R> {
+    fn compile_bytecode(
+        &mut self,
+        source: Source,
+        extra_scope: Option<ExtraScope>,
+    ) -> Result<InstructionPtr> {
+        let root = self.downgrade(source, extra_scope)?;
+        let ip = crate::compile_bytecode(root.as_ref(), self);
+        Ok(ip)
+    }
+
+    fn downgrade(&mut self, source: Source, extra_scope: Option<ExtraScope>) -> Result<OwnedIr> {
+        tracing::debug!("Parsing Nix expression");
+
+        self.code.sources.push(source.clone());
+
+        let root = rnix::Root::parse(&source.src);
+        handle_parse_error(root.errors(), source.clone()).map_or(Ok(()), Err)?;
+
+        tracing::debug!("Downgrading Nix expression");
+        let expr = root
+            .tree()
+            .expr()
+            .ok_or_else(|| Error::parse_error("unexpected EOF".into()))?;
+        let bump = Bump::new();
+        GhostToken::new(|token| {
+            let downgrade_ctx = DowngradeCtx::new(
+                &bump,
+                token,
+                self.runtime,
+                &self.code.global_env,
+                extra_scope.map(Into::into),
+                &mut self.code.thunk_count,
+                source,
+            );
+            let ir = downgrade_ctx.downgrade_toplevel(expr)?;
+            let ir = unsafe { std::mem::transmute::<RawIrRef<'_>, RawIrRef<'static>>(ir) };
+            Ok(OwnedIr { _bump: bump, ir })
+        })
+    }
+}
+
+impl<'a, R: VmRuntimeCtx> BytecodeContext for CompilerCtx<'a, R> {
+    fn intern_string(&mut self, s: &str) -> StringId {
+        self.runtime.intern_string(s)
+    }
+
+    fn register_span(&mut self, range: rnix::TextRange) -> u32 {
+        let id = self.code.spans.len();
+        let source_id = self
+            .code
+            .sources
+            .len()
+            .checked_sub(1)
+            .expect("current_source not set");
+        self.code.spans.push((source_id, range));
+        id as u32
+    }
+
+    fn get_code(&self) -> &[u8] {
+        &self.code.bytecode
+    }
+
+    fn get_code_mut(&mut self) -> &mut Vec<u8> {
+        &mut self.code.bytecode
+    }
+
+    fn add_constant(&mut self, val: Const) -> u32 {
+        use Const::*;
+        let val = match val {
+            Smi(x) => StaticValue::new_inline(x),
+            Float(x) => StaticValue::new_float(x),
+            Bool(x) => StaticValue::new_inline(x),
+            String(x) => StaticValue::new_inline(x),
+            Path(x) => StaticValue::new_inline(fix_runtime::Path(x)),
+            PrimOp {
+                id,
+                arity,
+                dispatch_ip,
+            } => StaticValue::new_primop(id, arity, dispatch_ip),
+            Null => StaticValue::default(),
+        };
+        self.runtime.add_const(val)
+    }
+
+    fn current_source_dir(&mut self) -> StringId {
+        let dir = self
+            .code
+            .sources
+            .last()
+            .expect("current_source not set")
+            .get_dir()
+            .to_string_lossy()
+            .into_owned();
+        self.runtime.intern_string(dir)
+    }
+}
+
+fn parse_error_span(error: &rnix::ParseError) -> Option<rnix::TextRange> {
+    use rnix::ParseError::*;
+    match error {
+        Unexpected(range)
+        | UnexpectedExtra(range)
+        | UnexpectedWanted(_, range, _)
+        | UnexpectedDoubleBind(range)
+        | DuplicatedArgs(range, _) => Some(*range),
+        _ => None,
+    }
+}
+
+fn handle_parse_error<'a>(
+    errors: impl IntoIterator<Item = &'a rnix::ParseError>,
+    source: Source,
+) -> Option<Box<Error>> {
+    for err in errors {
+        if let Some(span) = parse_error_span(err) {
+            return Some(
+                Error::parse_error(err.to_string())
+                    .with_source(source)
+                    .with_span(span),
+            );
+        }
+    }
+    None
+}
+
+struct DowngradeCtx<'ctx, 'id, 'ir, R: VmRuntimeCtx> {
+    bump: &'ir Bump,
+    token: GhostToken<'id>,
+    runtime: &'ctx mut R,
+    source: Source,
+    scopes: Vec<Scope<'ctx, 'id, 'ir>>,
+    with_stack: Vec<GhostRoMaybeThunkRef<'id, 'ir>>,
+    thunk_count: &'ctx mut usize,
+    thunk_scopes: Vec<ThunkScope<'id, 'ir>>,
+}
+
+impl<'ctx, 'id, 'ir, R: VmRuntimeCtx> DowngradeCtx<'ctx, 'id, 'ir, R> {
+    fn new(
+        bump: &'ir Bump,
+        token: GhostToken<'id>,
+        runtime: &'ctx mut R,
+        global: &'ctx HashMap<StringId, MaybeThunk>,
+        extra_scope: Option<Scope<'ctx, 'id, 'ir>>,
+        thunk_count: &'ctx mut usize,
+        source: Source,
+    ) -> Self {
+        Self {
+            bump,
+            token,
+            runtime,
+            source,
+            scopes: std::iter::once(Scope::Global(global))
+                .chain(extra_scope)
+                .collect(),
+            thunk_count,
+            with_stack: Vec::new(),
+            thunk_scopes: vec![ThunkScope::new_in(bump)],
+        }
+    }
+}
+
+impl<'ctx: 'ir, 'id, 'ir, R: VmRuntimeCtx> DowngradeContext<'id, 'ir>
+    for DowngradeCtx<'ctx, 'id, 'ir, R>
+{
+    fn new_expr(&self, expr: Ir<'ir, GhostRoRef<'id, 'ir>>) -> GhostRoIrRef<'id, 'ir> {
+        self.bump.alloc(GhostCell::new(expr).into())
+    }
+
+    fn maybe_thunk(&mut self, ir: GhostRoIrRef<'id, 'ir>) -> GhostRoMaybeThunkRef<'id, 'ir> {
+        use MaybeThunk::*;
+        let expr = (|| {
+            let expr = match *ir.borrow(&self.token) {
+                Ir::Builtin(x) => Builtin(x),
+                Ir::Int(x) => Int(x),
+                Ir::Float(x) => Float(x),
+                Ir::Bool(x) => Bool(x),
+                Ir::Str(x) => Str(x),
+                Ir::Arg { layer } => Arg { layer },
+                Ir::Builtins => Builtins,
+                Ir::Null => Null,
+                Ir::MaybeThunk(thunk) => return Some(thunk),
+                _ => return None,
+            };
+            Some(self.bump.alloc(GhostCell::new(expr).into()))
+        })();
+        if let Some(thunk) = expr {
+            return thunk;
+        }
+        let id = ThunkId(*self.thunk_count);
+        *self.thunk_count = self.thunk_count.checked_add(1).expect("thunk id overflow");
+        self.thunk_scopes
+            .last_mut()
+            .expect("no active cache scope")
+            .add_binding(id, ir);
+        self.bump.alloc(GhostCell::new(Thunk(id)).into())
+    }
+
+    fn intern_string(&mut self, sym: impl AsRef<str>) -> StringId {
+        self.runtime.intern_string(sym)
+    }
+
+    fn resolve_sym(&self, id: StringId) -> Symbol<'_> {
+        self.runtime.resolve_string(id).into()
+    }
+
+    fn lookup(
+        &mut self,
+        sym: StringId,
+        span: rnix::TextRange,
+    ) -> Result<GhostRoMaybeThunkRef<'id, 'ir>> {
+        for scope in self.scopes.iter().rev() {
+            match scope {
+                &Scope::Global(global_scope) => {
+                    if let Some(expr) = global_scope.get(&sym) {
+                        return Ok(expr.into());
+                    }
+                }
+                &Scope::Repl(repl_bindings) => {
+                    if repl_bindings.contains(&sym) {
+                        return Ok(self
+                            .bump
+                            .alloc(GhostCell::new(MaybeThunk::ReplBinding(sym)).into()));
+                    }
+                }
+                &Scope::ScopedImport { ref keys, slot_id } => {
+                    if keys.contains(&sym) {
+                        return Ok(self.bump.alloc(
+                            GhostCell::new(MaybeThunk::ScopedImportBinding { sym, slot_id }).into(),
+                        ));
+                    }
+                }
+                Scope::Let(let_scope) => {
+                    if let Some(&expr) = let_scope.get(&sym) {
+                        return Ok(expr.into());
+                    }
+                }
+                &Scope::Param {
+                    sym: param_sym,
+                    abs_layer,
+                } => {
+                    if param_sym == sym {
+                        let layers: u8 =
+                            self.thunk_scopes.len().try_into().expect("scope too deep!");
+                        let layer = layers - abs_layer;
+                        return Ok(self
+                            .bump
+                            .alloc(GhostCell::new(MaybeThunk::Arg { layer }).into()));
+                    }
+                }
+            }
+        }
+
+        if !self.with_stack.is_empty() {
+            let id = ThunkId(*self.thunk_count);
+            *self.thunk_count = self.thunk_count.checked_add(1).expect("thunk id overflow");
+            let mut namespaces =
+                bumpalo::collections::Vec::with_capacity_in(self.with_stack.len(), self.bump);
+            namespaces.extend(self.with_stack.iter().rev().copied());
+            let body = self
+                .bump
+                .alloc(GhostCell::new(Ir::WithLookup { sym, namespaces }).into());
+            self.thunk_scopes
+                .last_mut()
+                .expect("no active thunk scope")
+                .add_binding(id, body);
+            Ok(self
+                .bump
+                .alloc(GhostCell::new(MaybeThunk::Thunk(id)).into()))
+        } else {
+            Err(Error::downgrade_error(
+                format!("'{}' not found", self.resolve_sym(sym)),
+                self.get_current_source(),
+                span,
+            ))
+        }
+    }
+
+    fn get_current_source(&self) -> Source {
+        self.source.clone()
+    }
+
+    fn with_let_scope<F, Ret>(&mut self, keys: &[StringId], f: F) -> Result<Ret>
+    where
+        F: FnOnce(
+            &mut Self,
+        ) -> Result<(
+            bumpalo::collections::Vec<'ir, GhostRoMaybeThunkRef<'id, 'ir>>,
+            Ret,
+        )>,
+    {
+        let base = *self.thunk_count;
+        *self.thunk_count = self
+            .thunk_count
+            .checked_add(keys.len())
+            .expect("thunk id overflow");
+        let handles = (base..base + keys.len())
+            .map(|id| {
+                &*self
+                    .bump
+                    .alloc(GhostCell::new(MaybeThunk::Thunk(ThunkId(id))))
+            })
+            .collect::<Vec<_>>();
+        let scope = keys.iter().copied().zip(handles.iter().copied()).collect();
+        self.scopes.push(Scope::Let(scope));
+        let (vals, ret) = { f(self)? };
+        self.scopes.pop();
+        assert_eq!(keys.len(), vals.len());
+        let scope = self.thunk_scopes.last_mut().expect("no active thunk scope");
+        for (i, (val, handle)) in vals.into_iter().zip(handles).enumerate() {
+            let thunk = *val.borrow(&self.token);
+            *handle.borrow_mut(&mut self.token) = thunk;
+            let id = ThunkId(base + i);
+            let ir_ref = self
+                .bump
+                .alloc(GhostCell::new(Ir::MaybeThunk(handle.into())).into());
+            scope.add_binding(id, ir_ref);
+        }
+        Ok(ret)
+    }
+
+    fn with_param_scope<F, Ret>(&mut self, sym: StringId, f: F) -> Ret
+    where
+        F: FnOnce(&mut Self) -> Ret,
+    {
+        self.scopes.push(Scope::Param {
+            sym,
+            abs_layer: self.thunk_scopes.len().try_into().expect("scope too deep!"),
+        });
+        let mut guard = ScopeGuard { ctx: self };
+        f(guard.as_ctx())
+    }
+
+    fn with_with_scope<F, Ret>(&mut self, namespace: GhostRoMaybeThunkRef<'id, 'ir>, f: F) -> Ret
+    where
+        F: FnOnce(&mut Self) -> Ret,
+    {
+        self.with_stack.push(namespace);
+        let ret = f(self);
+        self.with_stack.pop();
+        ret
+    }
+
+    fn with_thunk_scope<F, Ret>(
+        &mut self,
+        f: F,
+    ) -> (
+        Ret,
+        bumpalo::collections::Vec<'ir, (ThunkId, GhostRoIrRef<'id, 'ir>)>,
+    )
+    where
+        F: FnOnce(&mut Self) -> Ret,
+    {
+        if self.thunk_scopes.len() == u8::MAX as usize {
+            panic!("scope too deep!");
+        }
+        self.thunk_scopes.push(ThunkScope::new_in(self.bump));
+        let ret = f(self);
+        (
+            ret,
+            self.thunk_scopes
+                .pop()
+                .expect("no thunk scope left???")
+                .bindings,
+        )
+    }
+
+    fn bump(&self) -> &'ir bumpalo::Bump {
+        self.bump
+    }
+}
+
+impl<'id, 'ir, 'ctx: 'ir, R: VmRuntimeCtx> DowngradeCtx<'ctx, 'id, 'ir, R> {
+    fn downgrade_toplevel(mut self, root: rnix::ast::Expr) -> Result<RawIrRef<'ir>> {
+        let body = root.downgrade(&mut self)?;
+        let thunks = self
+            .thunk_scopes
+            .pop()
+            .expect("no thunk scope left???")
+            .bindings;
+        Ok(Ir::freeze(
+            self.new_expr(Ir::TopLevel { body, thunks }),
+            self.token,
+        ))
+    }
+}
+
+struct ThunkScope<'id, 'ir> {
+    bindings: bumpalo::collections::Vec<'ir, (ThunkId, GhostRoIrRef<'id, 'ir>)>,
+}
+
+impl<'id, 'ir> ThunkScope<'id, 'ir> {
+    fn new_in(bump: &'ir Bump) -> Self {
+        Self {
+            bindings: bumpalo::collections::Vec::new_in(bump),
+        }
+    }
+
+    fn add_binding(&mut self, id: ThunkId, ir: GhostRoIrRef<'id, 'ir>) {
+        self.bindings.push((id, ir));
+    }
+}
+
+enum Scope<'ctx, 'id, 'ir> {
+    Global(&'ctx HashMap<StringId, MaybeThunk>),
+    Repl(&'ctx HashSet<StringId>),
+    ScopedImport {
+        keys: HashSet<StringId>,
+        #[allow(dead_code)]
+        slot_id: u32,
+    },
+    Let(HashMap<StringId, GhostMaybeThunkRef<'id, 'ir>>),
+    Param {
+        sym: StringId,
+        abs_layer: u8,
+    },
+}
+
+pub enum ExtraScope<'ctx> {
+    Repl(&'ctx HashSet<StringId>),
+    ScopedImport {
+        keys: HashSet<StringId>,
+        slot_id: u32,
+    },
+}
+
+impl<'ctx> From<ExtraScope<'ctx>> for Scope<'ctx, '_, '_> {
+    fn from(value: ExtraScope<'ctx>) -> Self {
+        use ExtraScope::*;
+        match value {
+            ScopedImport { keys, slot_id } => Scope::ScopedImport { keys, slot_id },
+            Repl(scope) => Scope::Repl(scope),
+        }
+    }
+}
+
+struct ScopeGuard<'a, 'ctx, 'id, 'ir, R: VmRuntimeCtx> {
+    ctx: &'a mut DowngradeCtx<'ctx, 'id, 'ir, R>,
+}
+
+impl<'a, 'ctx, 'id, 'ir, R: VmRuntimeCtx> Drop for ScopeGuard<'a, 'ctx, 'id, 'ir, R> {
+    fn drop(&mut self) {
+        self.ctx.scopes.pop();
+    }
+}
+
+impl<'a, 'ctx, 'id, 'ir, R: VmRuntimeCtx> ScopeGuard<'a, 'ctx, 'id, 'ir, R> {
+    fn as_ctx(&mut self) -> &mut DowngradeCtx<'ctx, 'id, 'ir, R> {
+        self.ctx
+    }
+}
+
+struct OwnedIr {
+    _bump: Bump,
+    ir: RawIrRef<'static>,
+}
+
+impl OwnedIr {
+    fn as_ref<'ir>(&'ir self) -> RawIrRef<'ir> {
+        unsafe { std::mem::transmute::<RawIrRef<'static>, RawIrRef<'ir>>(self.ir) }
+    }
+}

fix-compiler/src/ir.rs

@@ -0,0 +1,329 @@
+use std::hash::Hash;
+use std::marker::PhantomData;
+
+use bumpalo::Bump;
+use bumpalo::collections::Vec;
+use fix_lang::{BUILTINS, BuiltinId, StringId};
+use ghost_cell::{GhostCell, GhostToken};
+use rnix::{TextRange, ast};
+use string_interner::DefaultStringInterner;
+
+pub mod downgrade;
+
+pub type HashMap<'ir, K, V> = hashbrown::HashMap<K, V, hashbrown::DefaultHashBuilder, &'ir Bump>;
+
+pub type GhostIrRef<'id, 'ir> = <GhostRef<'id, 'ir> as RefExt<'ir>>::IrRef;
+pub type GhostRoIrRef<'id, 'ir> = <GhostRoRef<'id, 'ir> as RefExt<'ir>>::IrRef;
+pub type RawIrRef<'ir> = <RawRef<'ir> as RefExt<'ir>>::IrRef;
+pub type GhostMaybeThunkRef<'id, 'ir> = <GhostRef<'id, 'ir> as RefExt<'ir>>::MaybeThunkRef;
+pub type GhostRoMaybeThunkRef<'id, 'ir> = <GhostRoRef<'id, 'ir> as RefExt<'ir>>::MaybeThunkRef;
+
+impl<'id, 'ir> Ir<'ir, GhostRoRef<'id, 'ir>> {
+    /// Freeze a mutable IR reference into a read-only one, consuming the
+    /// `GhostToken` to prevent any further mutation.
+    pub fn freeze(this: GhostRoIrRef<'id, 'ir>, _: GhostToken<'id>) -> RawIrRef<'ir> {
+        // SAFETY: The transmute is sound because:
+        // - `GhostCell<'id, T>` is `#[repr(transparent)]` over `T`, so
+        //   `&'ir GhostCell<'id, T>` and `&'ir T` have identical layout.
+        // - `Ir<'ir, R>` is `#[repr(C)]`, and for every field that depends on
+        //   `R`, instantiating `R = GhostRef<'id, 'ir>` vs `R = RawRef<'ir>`
+        //   produces types of identical layout:
+        //     - `R::IrRef` becomes `&'ir GhostCell<'id, Ir<...>>` vs `&'ir Ir<...>`
+        //     - `R::MaybeThunkRef` becomes `&'ir GhostCell<'id, MaybeThunk>`
+        //       vs `&'ir MaybeThunk`
+        //     - `R::Ref<Ir<'ir, R>>` (used in `ConcatStrings::parts`) reduces
+        //       to the same case as `R::IrRef`
+        // - Therefore `IrRef<'id, 'ir>` and `RawIrRef<'ir>` are both
+        //   pointer-sized references with the same layout.
+        //
+        // Consuming the `GhostToken` guarantees no `borrow_mut` calls can
+        // occur afterwards, so the shared `&Ir` references reachable from a
+        // `RawIrRef<'ir>` can never alias with mutable references.
+        unsafe { std::mem::transmute::<GhostRoIrRef<'id, 'ir>, RawIrRef<'ir>>(this) }
+    }
+}
+
+#[repr(transparent)]
+pub struct GhostRoCell<'id, T: ?Sized>(GhostCell<'id, T>);
+
+impl<'id, T> From<GhostCell<'id, T>> for GhostRoCell<'id, T> {
+    fn from(value: GhostCell<'id, T>) -> Self {
+        Self(value)
+    }
+}
+
+impl<'id, T: ?Sized> From<&GhostCell<'id, T>> for &GhostRoCell<'id, T> {
+    fn from(value: &GhostCell<'id, T>) -> Self {
+        // SAFETY: `GhostRoCell` is `#[repr(transparent)]` over `GhostCell`
+        // TODO: document mutability
+        unsafe { std::mem::transmute(value) }
+    }
+}
+
+impl<'id, T: ?Sized> From<&T> for &GhostRoCell<'id, T> {
+    fn from(value: &T) -> Self {
+        // SAFETY: `GhostRoCell` is `#[repr(transparent)]` over `GhostCell`,
+        //         which is `#[repr(transparent)]` over `T`
+        // TODO: document mutability
+        unsafe { std::mem::transmute(value) }
+    }
+}
+
+impl<'id, T: ?Sized> GhostRoCell<'id, T> {
+    pub fn borrow<'a>(&'a self, token: &'a GhostToken<'id>) -> &'a T {
+        self.0.borrow(token)
+    }
+}
+
+#[repr(C)]
+#[derive(Debug, Clone, Copy)]
+pub enum MaybeThunk {
+    Int(i64),
+    Float(f64),
+    Bool(bool),
+    Null,
+    Str(StringId),
+    Path(StringId),
+    Thunk(ThunkId),
+    Arg { layer: u8 },
+    Builtin(BuiltinId),
+    BuiltinConst(StringId),
+    Builtins,
+    ReplBinding(StringId),
+    ScopedImportBinding { slot_id: u32, sym: StringId },
+}
+
+pub trait Ref<'ir> {
+    type Ref<T>
+    where
+        T: 'ir;
+}
+
+pub trait RefExt<'ir>: Ref<'ir> {
+    type Ir;
+    type IrRef;
+    type MaybeThunkRef;
+}
+impl<'ir, T: Ref<'ir> + 'ir> RefExt<'ir> for T {
+    type Ir = Ir<'ir, Self>;
+    type IrRef = Self::Ref<Self::Ir>;
+    type MaybeThunkRef = Self::Ref<MaybeThunk>;
+}
+
+pub struct GhostRef<'id, 'ir>(PhantomData<&'ir GhostCell<'id, ()>>);
+pub struct GhostRoRef<'id, 'ir>(PhantomData<&'ir GhostRoCell<'id, ()>>);
+pub struct RawRef<'ir>(PhantomData<&'ir ()>);
+
+impl<'id, 'ir> Ref<'ir> for GhostRef<'id, 'ir> {
+    type Ref<T: 'ir> = &'ir GhostCell<'id, T>;
+}
+impl<'id, 'ir> Ref<'ir> for GhostRoRef<'id, 'ir> {
+    type Ref<T: 'ir> = &'ir GhostRoCell<'id, T>;
+}
+impl<'ir> Ref<'ir> for RawRef<'ir> {
+    type Ref<T: 'ir> = &'ir T;
+}
+
+#[repr(C)]
+#[derive(Debug)]
+pub enum Ir<'ir, R: RefExt<'ir> + ?Sized + 'ir> {
+    Int(i64),
+    Float(f64),
+    Bool(bool),
+    Null,
+    Str(StringId),
+    Path(R::IrRef),
+    AttrSet {
+        stcs: HashMap<'ir, StringId, (R::MaybeThunkRef, TextRange)>,
+        dyns: Vec<'ir, (R::IrRef, R::MaybeThunkRef, TextRange)>,
+    },
+    List {
+        items: Vec<'ir, R::MaybeThunkRef>,
+    },
+    ConcatStrings {
+        parts: Vec<'ir, R::Ref<Ir<'ir, R>>>,
+        force_string: bool,
+    },
+
+    // OPs
+    UnOp {
+        rhs: R::IrRef,
+        kind: UnOpKind,
+    },
+    BinOp {
+        lhs: R::IrRef,
+        rhs: R::IrRef,
+        kind: BinOpKind,
+    },
+    HasAttr {
+        lhs: R::IrRef,
+        rhs: Vec<'ir, Attr<R::IrRef>>,
+    },
+    Select {
+        expr: R::IrRef,
+        attrpath: Vec<'ir, Attr<R::IrRef>>,
+        default: Option<R::IrRef>,
+        span: TextRange,
+    },
+
+    // Conditionals
+    If {
+        cond: R::IrRef,
+        consq: R::IrRef,
+        alter: R::IrRef,
+    },
+    Assert {
+        assertion: R::IrRef,
+        expr: R::IrRef,
+        assertion_raw: String,
+        span: TextRange,
+    },
+
+    WithLookup {
+        sym: StringId,
+        namespaces: Vec<'ir, R::MaybeThunkRef>,
+    },
+
+    // Function related
+    Func {
+        body: R::IrRef,
+        param: Option<Param<'ir>>,
+        thunks: Vec<'ir, (ThunkId, R::IrRef)>,
+    },
+    Arg {
+        layer: u8,
+    },
+    Call {
+        func: R::IrRef,
+        arg: R::MaybeThunkRef,
+        span: TextRange,
+    },
+
+    // Builtins
+    Builtins,
+    Builtin(BuiltinId),
+    BuiltinConst(StringId),
+
+    // Misc
+    TopLevel {
+        body: R::IrRef,
+        thunks: Vec<'ir, (ThunkId, R::IrRef)>,
+    },
+    MaybeThunk(R::MaybeThunkRef),
+    ReplBinding(StringId),
+    ScopedImportBinding {
+        sym: StringId,
+        slot_id: u32,
+    },
+}
+
+#[repr(transparent)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct ThunkId(pub usize);
+
+/// Represents a key in an attribute path.
+#[allow(unused)]
+#[derive(Debug)]
+pub enum Attr<Ref> {
+    /// A dynamic attribute key, which is an expression that must evaluate to a string.
+    /// Example: `attrs.${key}`
+    Dynamic(Ref, TextRange),
+    /// A static attribute key.
+    /// Example: `attrs.key`
+    Str(StringId, TextRange),
+}
+
+/// The kinds of binary operations supported in Nix.
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
+pub enum BinOpKind {
+    // Arithmetic
+    Add,
+    Sub,
+    Div,
+    Mul,
+
+    // Comparison
+    Eq,
+    Neq,
+    Lt,
+    Gt,
+    Leq,
+    Geq,
+
+    // Logical
+    And,
+    Or,
+    Impl,
+
+    // Set/String/Path operations
+    Con, // List concatenation (`++`)
+    Upd, // AttrSet update (`//`)
+}
+
+/// The kinds of unary operations.
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
+pub enum UnOpKind {
+    Neg, // Negation (`-`)
+    Not, // Logical not (`!`)
+}
+
+impl From<ast::UnaryOpKind> for UnOpKind {
+    fn from(value: ast::UnaryOpKind) -> Self {
+        match value {
+            ast::UnaryOpKind::Invert => UnOpKind::Not,
+            ast::UnaryOpKind::Negate => UnOpKind::Neg,
+        }
+    }
+}
+
+/// Describes the parameters of a function.
+#[derive(Debug)]
+pub struct Param<'ir> {
+    pub required: Vec<'ir, (StringId, TextRange)>,
+    pub optional: Vec<'ir, (StringId, TextRange)>,
+    pub ellipsis: bool,
+}
+
+pub fn new_global_env(
+    strings: &mut DefaultStringInterner,
+) -> hashbrown::HashMap<StringId, MaybeThunk> {
+    let mut global_env = hashbrown::HashMap::new();
+    let builtins_sym = StringId(strings.get_or_intern("builtins"));
+    global_env.insert(builtins_sym, MaybeThunk::Builtins);
+
+    for (idx, &(name, _)) in BUILTINS.iter().enumerate() {
+        let id = BuiltinId::try_from(idx as u8).expect("infallible");
+        let name = StringId(strings.get_or_intern(name));
+        global_env.insert(name, MaybeThunk::Builtin(id));
+    }
+
+    let consts = [
+        (
+            "__currentSystem",
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("currentSystem"))),
+        ),
+        ("__langVersion", MaybeThunk::Int(6)),
+        (
+            "__nixVersion",
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("nixVersion"))),
+        ),
+        (
+            "__storeDir",
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("storeDir"))),
+        ),
+        (
+            "__nixPath",
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("nixPath"))),
+        ),
+        ("null", MaybeThunk::Null),
+        ("true", MaybeThunk::Bool(true)),
+        ("false", MaybeThunk::Bool(false)),
+    ];
+
+    for (name, ir) in consts {
+        let name = StringId(strings.get_or_intern(name));
+        global_env.insert(name, ir);
+    }
+
+    global_env
+}

fix-compiler/src/ir/downgrade.rs

@@ -1,15 +1,13 @@
-use bumpalo::boxed::Box;
 use bumpalo::collections::{CollectIn, Vec};
+use fix_error::{Error, Result, Source};
+use fix_lang::{BuiltinId, Symbol};
 use hashbrown::HashSet;
 use hashbrown::hash_map::Entry;
 use rnix::TextRange;
-use rnix::ast::{self, Expr, HasEntry};
+use rnix::ast::{self, AstToken, Expr, HasEntry};
 use rowan::ast::AstNode;
 
-use crate::error::{Error, Result, Source};
+use super::*;
-use crate::ir::*;
-use crate::runtime::BuiltinId;
-use crate::value::Symbol;
 
 trait Require<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, T> {
     fn require(self, ctx: &Ctx, span: TextRange) -> Result<T>;
@@ -39,20 +37,13 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, T, E: std::fmt::Display>
     }
 }
 
-trait BoxIn: Sized {
-    fn box_in(self, bump: &bumpalo::Bump) -> Box<'_, Self> {
-        Box::new_in(self, bump)
-    }
-}
-impl<T: Sized> BoxIn for T {}
-
 pub trait DowngradeContext<'id: 'ir, 'ir> {
-    fn new_expr(&self, expr: Ir<'ir, IrRef<'id, 'ir>>) -> IrRef<'id, 'ir>;
+    fn new_expr(&self, expr: Ir<'ir, GhostRoRef<'id, 'ir>>) -> GhostRoIrRef<'id, 'ir>;
-    fn maybe_thunk(&mut self, ir: IrRef<'id, 'ir>) -> IrRef<'id, 'ir>;
+    fn maybe_thunk(&mut self, ir: GhostRoIrRef<'id, 'ir>) -> GhostRoMaybeThunkRef<'id, 'ir>;
 
-    fn new_sym(&mut self, sym: String) -> StringId;
+    fn intern_string(&mut self, sym: impl AsRef<str>) -> StringId;
-    fn get_sym(&self, id: StringId) -> Symbol<'_>;
+    fn resolve_sym(&self, id: StringId) -> Symbol<'_>;
-    fn lookup(&self, sym: StringId, span: TextRange) -> Result<IrRef<'id, 'ir>>;
+    fn lookup(&mut self, sym: StringId, span: TextRange) -> Result<GhostRoMaybeThunkRef<'id, 'ir>>;
 
     fn get_current_source(&self) -> Source;
 
@@ -61,11 +52,11 @@ pub trait DowngradeContext<'id: 'ir, 'ir> {
         F: FnOnce(&mut Self) -> R;
     fn with_let_scope<F, R>(&mut self, bindings: &[StringId], f: F) -> Result<R>
     where
-        F: FnOnce(&mut Self) -> Result<(Vec<'ir, IrRef<'id, 'ir>>, R)>;
+        F: FnOnce(&mut Self) -> Result<(Vec<'ir, GhostRoMaybeThunkRef<'id, 'ir>>, R)>;
-    fn with_with_scope<F, R>(&mut self, f: F) -> R
+    fn with_with_scope<F, R>(&mut self, namespace: GhostRoMaybeThunkRef<'id, 'ir>, f: F) -> R
     where
         F: FnOnce(&mut Self) -> R;
-    fn with_thunk_scope<F, R>(&mut self, f: F) -> (R, Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>)
+    fn with_thunk_scope<F, R>(&mut self, f: F) -> (R, Vec<'ir, (ThunkId, GhostRoIrRef<'id, 'ir>)>)
     where
         F: FnOnce(&mut Self) -> R;
 
@@ -73,11 +64,11 @@ pub trait DowngradeContext<'id: 'ir, 'ir> {
 }
 
 pub trait Downgrade<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>>;
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>>;
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for Expr {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         use Expr::*;
         match self {
             Apply(apply) => apply.downgrade(ctx),
@@ -106,7 +97,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
             AttrSet(attrs) => attrs.downgrade(ctx),
             UnaryOp(op) => op.downgrade(ctx),
             Ident(ident) => ident.downgrade(ctx),
-            CurPos(curpos) => Ok(ctx.new_expr(Ir::CurPos(curpos.syntax().text_range()))),
+            CurPos(curpos) => curpos.downgrade(ctx),
             With(with) => with.downgrade(ctx),
             HasAttr(has) => has.downgrade(ctx),
             Paren(paren) => paren
@@ -122,7 +113,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Assert {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let assertion = self.condition().require(ctx, span)?;
         let assertion_raw = assertion.to_string();
@@ -138,7 +129,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::IfElse {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let cond = self.condition().require(ctx, span)?.downgrade(ctx)?;
         let consq = self.body().require(ctx, span)?.downgrade(ctx)?;
@@ -150,9 +141,8 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 macro_rules! path {
     ($ty:ident) => {
         impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::$ty {
-            fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+            fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
-                let span = self.syntax().text_range();
+                downgrade_path(self.parts(), ctx)
-                downgrade_path(self.parts(), span, ctx)
             }
         }
     };
@@ -161,19 +151,20 @@ path!(PathAbs);
 path!(PathRel);
 path!(PathHome);
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::PathSearch {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let path = {
             let temp = self.content().require(ctx, span)?;
             let text = temp.text();
-            ctx.new_expr(Ir::Str(
+            let id = ctx.intern_string(&text[1..text.len() - 1]);
-                text[1..text.len() - 1].to_string().box_in(ctx.bump()),
+            let expr = ctx.new_expr(Ir::Str(id));
-            ))
+            ctx.maybe_thunk(expr)
         };
         // HACK: disgusting eww
         let find_file = ctx.new_expr(Ir::Builtin(BuiltinId::FindFile));
-        let sym = ctx.new_sym("nixPath".into());
+        let sym = ctx.intern_string("nixPath");
         let nix_path = ctx.new_expr(Ir::BuiltinConst(sym));
+        let nix_path = ctx.maybe_thunk(nix_path);
         let call = ctx.new_expr(Ir::Call {
             func: find_file,
             arg: nix_path,
@@ -188,21 +179,21 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Str {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let normalized = self.normalized_parts();
         let is_single_literal = normalized.len() == 1
             && matches!(normalized.first(), Some(ast::InterpolPart::Literal(_)));
 
         let bump = ctx.bump();
         let mut parts = normalized.into_iter().map(|part| match part {
-            ast::InterpolPart::Literal(lit) => Ok(ctx.new_expr(Ir::Str(lit.box_in(bump)))),
+            ast::InterpolPart::Literal(lit) => {
-            ast::InterpolPart::Interpolation(interpol) => {
+                let id = ctx.intern_string(lit);
-                let inner = interpol
+                Ok(ctx.new_expr(Ir::Str(id)))
-                    .expr()
-                    .require(ctx, interpol.syntax().text_range())?
-                    .downgrade(ctx)?;
-                Ok(ctx.maybe_thunk(inner))
             }
+            ast::InterpolPart::Interpolation(interpol) => interpol
+                .expr()
+                .require(ctx, interpol.syntax().text_range())?
+                .downgrade(ctx),
         });
 
         Ok(if is_single_literal {
@@ -218,27 +209,88 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Literal {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
-        Ok(ctx.new_expr(match self.kind() {
+        let expr = match self.kind() {
             ast::LiteralKind::Integer(int) => Ir::Int(int.value().require(ctx, span)?),
             ast::LiteralKind::Float(float) => Ir::Float(float.value().require(ctx, span)?),
-            ast::LiteralKind::Uri(uri) => Ir::Str(uri.to_string().box_in(ctx.bump())),
+            ast::LiteralKind::Uri(uri) => {
-        }))
+                let id = ctx.intern_string(uri.syntax().text());
+                Ir::Str(id)
+            }
+        };
+        Ok(ctx.new_expr(expr))
     }
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Ident {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let text = self.ident_token().require(ctx, span)?.to_string();
-        let sym = ctx.new_sym(text);
+        let sym = ctx.intern_string(text);
         ctx.lookup(sym, span)
+            .map(|thunk| ctx.new_expr(Ir::MaybeThunk(thunk)))
+    }
+}
+
+impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::CurPos {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
+        fn byte_offset_to_line_col(content: &str, offset: usize) -> (u32, u32) {
+            let mut line = 1u32;
+            let mut col = 1u32;
+
+            for (idx, ch) in content.char_indices() {
+                if idx >= offset {
+                    break;
+                }
+                if ch == '\n' {
+                    line += 1;
+                    col = 1;
+                } else {
+                    col += 1;
+                }
+            }
+
+            (line, col)
+        }
+
+        let span = self.syntax().text_range();
+        let source = ctx.get_current_source();
+        let (line, column) = byte_offset_to_line_col(&source.src, span.start().into());
+
+        let file_sym = ctx.intern_string("file");
+        let line_sym = ctx.intern_string("line");
+        let column_sym = ctx.intern_string("column");
+
+        let file: GhostRoMaybeThunkRef = ctx
+            .bump()
+            .alloc(GhostCell::new(MaybeThunk::Str(ctx.intern_string(source.get_name()))).into());
+        let line = ctx
+            .bump()
+            .alloc(GhostCell::new(MaybeThunk::Int(i64::from(line))).into());
+        let column = ctx
+            .bump()
+            .alloc(GhostCell::new(MaybeThunk::Int(i64::from(column))).into());
+
+        let map = {
+            let mut map = HashMap::new_in(ctx.bump());
+
+            map.insert(file_sym, (file, TextRange::default()));
+            map.insert(line_sym, (line, TextRange::default()));
+            map.insert(column_sym, (column, TextRange::default()));
+
+            map
+        };
+
+        Ok(ctx.new_expr(Ir::AttrSet {
+            stcs: map,
+            dyns: Vec::new_in(ctx.bump()),
+        }))
     }
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::AttrSet {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let rec = self.rec_token().is_some();
         if !rec {
             let attrs = downgrade_attrs(self, ctx)?;
@@ -254,7 +306,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::List {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let bump = ctx.bump();
         let items = self
             .items()
@@ -268,17 +320,52 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::BinOp {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
+        use BinOpKind::*;
+        use ast::BinOpKind as Kind;
+
         let span = self.syntax().text_range();
         let lhs = self.lhs().require(ctx, span)?.downgrade(ctx)?;
         let rhs = self.rhs().require(ctx, span)?.downgrade(ctx)?;
-        let kind = self.operator().require(ctx, span)?.into();
+        let kind = match self.operator().require(ctx, span)? {
+            Kind::Concat => Con,
+            Kind::Update => Upd,
+            Kind::Add => Add,
+            Kind::Sub => Sub,
+            Kind::Mul => Mul,
+            Kind::Div => Div,
+            Kind::And => And,
+            Kind::Equal => Eq,
+            Kind::Implication => Impl,
+            Kind::Less => Lt,
+            Kind::LessOrEq => Leq,
+            Kind::More => Gt,
+            Kind::MoreOrEq => Geq,
+            Kind::NotEqual => Neq,
+            Kind::Or => Or,
+            Kind::PipeLeft => {
+                let arg = ctx.maybe_thunk(rhs);
+                return Ok(ctx.new_expr(Ir::Call {
+                    func: lhs,
+                    arg,
+                    span,
+                }));
+            }
+            Kind::PipeRight => {
+                let arg = ctx.maybe_thunk(lhs);
+                return Ok(ctx.new_expr(Ir::Call {
+                    func: rhs,
+                    arg,
+                    span,
+                }));
+            }
+        };
         Ok(ctx.new_expr(Ir::BinOp { lhs, rhs, kind }))
     }
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::HasAttr {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let lhs = self.expr().require(ctx, span)?.downgrade(ctx)?;
         let rhs = downgrade_attrpath(self.attrpath().require(ctx, span)?, ctx)?;
@@ -287,7 +374,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::UnaryOp {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let rhs = self.expr().require(ctx, span)?.downgrade(ctx)?;
         let kind = self.operator().require(ctx, span)?.into();
@@ -296,16 +383,14 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Select {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let expr = self.expr().require(ctx, span)?.downgrade(ctx)?;
         let attrpath = downgrade_attrpath(self.attrpath().require(ctx, span)?, ctx)?;
-        let default = if let Some(default) = self.default_expr() {
+        let default = self
-            let default_expr = default.downgrade(ctx)?;
+            .default_expr()
-            Some(ctx.maybe_thunk(default_expr))
+            .map(|expr| expr.downgrade(ctx))
-        } else {
+            .transpose()?;
-            None
-        };
         let span = self.syntax().text_range();
         Ok(ctx.new_expr(Ir::Select {
             expr,
@@ -317,7 +402,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::LegacyLet {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let entries: Vec<'ir, _> = self.entries().collect_in(ctx.bump());
         let attrset_expr = downgrade_let_bindings(entries, ctx, |ctx, binding_keys| {
@@ -332,7 +417,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
             Ok(ctx.new_expr(Ir::AttrSet { stcs, dyns }))
         })?;
 
-        let body_sym = ctx.new_sym("body".to_string());
+        let body_sym = ctx.intern_string("body");
         Ok(ctx.new_expr(Ir::Select {
             expr: attrset_expr,
             attrpath: Vec::from_iter_in(
@@ -346,7 +431,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::LetIn {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let entries: Vec<'ir, _> = self.entries().collect_in(ctx.bump());
         let span = self.syntax().text_range();
         let body_expr = self.body().require(ctx, span)?;
@@ -356,33 +441,25 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::With {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let namespace = self.namespace().require(ctx, span)?.downgrade(ctx)?;
         let namespace = ctx.maybe_thunk(namespace);
 
         let body_expr = self.body().require(ctx, span)?;
-        let (body, thunks) =
+        ctx.with_with_scope(namespace, |ctx| body_expr.downgrade(ctx))
-            ctx.with_thunk_scope(|ctx| ctx.with_with_scope(|ctx| body_expr.downgrade(ctx)));
-        let body = body?;
-
-        Ok(ctx.new_expr(Ir::With {
-            namespace,
-            body,
-            thunks,
-        }))
     }
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Lambda {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let raw_param = self.param().require(ctx, span)?;
         let body_ast = self.body().require(ctx, span)?;
 
         struct Ret<'id, 'ir> {
             param: Option<Param<'ir>>,
-            body: IrRef<'id, 'ir>,
+            body: GhostRoIrRef<'id, 'ir>,
         }
 
         let (ret, thunks) = ctx.with_thunk_scope(|ctx| {
@@ -391,7 +468,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 
             match raw_param {
                 ast::Param::IdentParam(id) => {
-                    let param_sym = ctx.new_sym(id.to_string());
+                    let param_sym = ctx.intern_string(id.to_string());
                     param = None;
 
                     body = ctx.with_param_scope(param_sym, |ctx| body_ast.downgrade(ctx))?;
@@ -401,7 +478,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
                         .pat_bind()
                         .map(|alias| {
                             let ident = alias.ident().require(ctx, alias.syntax().text_range())?;
-                            Ok::<_, std::boxed::Box<Error>>(ctx.new_sym(ident.to_string()))
+                            Ok::<_, std::boxed::Box<Error>>(ctx.intern_string(ident.to_string()))
                         })
                         .transpose()?;
 
@@ -439,7 +516,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Apply {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let func = self.lambda().require(ctx, span)?.downgrade(ctx)?;
         let arg = self.argument().require(ctx, span)?.downgrade(ctx)?;
@@ -485,7 +562,7 @@ impl<'id: 'ir, 'ir> PendingAttrSet<'ir> {
 
         match first {
             ast::Attr::Ident(ident) => {
-                let sym = ctx.new_sym(ident.to_string());
+                let sym = ctx.intern_string(ident.to_string());
                 self.insert_static(sym, span, rest, value, ctx)
             }
             ast::Attr::Str(string) => {
@@ -494,7 +571,7 @@ impl<'id: 'ir, 'ir> PendingAttrSet<'ir> {
                     && let ast::InterpolPart::Literal(lit) =
                         parts.into_iter().next().expect("len checked")
                 {
-                    let sym = ctx.new_sym(lit);
+                    let sym = ctx.intern_string(lit);
                     return self.insert_static(sym, span, rest, value, ctx);
                 }
                 self.insert_dynamic(first.clone(), span, rest, value, ctx)
@@ -737,14 +814,14 @@ impl<'id: 'ir, 'ir> PendingAttrSet<'ir> {
         for attr in inherit.attrs() {
             let span = attr.syntax().text_range();
             let sym = match &attr {
-                ast::Attr::Ident(ident) => ctx.new_sym(ident.to_string()),
+                ast::Attr::Ident(ident) => ctx.intern_string(ident.to_string()),
                 ast::Attr::Str(s) => {
                     let parts = s.normalized_parts();
                     if parts.len() == 1
                         && let ast::InterpolPart::Literal(lit) =
                             parts.into_iter().next().expect("len checked")
                     {
-                        ctx.new_sym(lit)
+                        ctx.intern_string(lit)
                     } else {
                         return Err(Error::downgrade_error(
                             "dynamic attributes not allowed in inherit".to_string(),
@@ -764,7 +841,7 @@ impl<'id: 'ir, 'ir> PendingAttrSet<'ir> {
 
             if self.stcs.contains_key(&sym) {
                 return Err(Error::downgrade_error(
-                    format!("attribute '{}' already defined", ctx.get_sym(sym)),
+                    format!("attribute '{}' already defined", ctx.resolve_sym(sym)),
                     ctx.get_current_source(),
                     span,
                 ));
@@ -841,8 +918,15 @@ fn make_attrpath_value_entry<'ir>(path: Vec<'ir, ast::Attr>, value: ast::Expr) -
 }
 
 struct FinalizedAttrSet<'id, 'ir> {
-    stcs: HashMap<'ir, StringId, (IrRef<'id, 'ir>, TextRange)>,
+    stcs: HashMap<'ir, StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
-    dyns: Vec<'ir, (IrRef<'id, 'ir>, IrRef<'id, 'ir>, TextRange)>,
+    dyns: Vec<
+        'ir,
+        (
+            GhostRoIrRef<'id, 'ir>,
+            GhostRoMaybeThunkRef<'id, 'ir>,
+            TextRange,
+        ),
+    >,
 }
 
 fn downgrade_attrs<'id, 'ir>(
@@ -857,22 +941,22 @@ fn downgrade_attrs<'id, 'ir>(
 fn downgrade_attr<'id, 'ir>(
     attr: ast::Attr,
     ctx: &mut impl DowngradeContext<'id, 'ir>,
-) -> Result<Attr<IrRef<'id, 'ir>>> {
+) -> Result<Attr<GhostRoIrRef<'id, 'ir>>> {
     use ast::Attr::*;
     use ast::InterpolPart::*;
     match attr {
         Ident(ident) => Ok(Attr::Str(
-            ctx.new_sym(ident.to_string()),
+            ctx.intern_string(ident.to_string()),
             ident.syntax().text_range(),
         )),
         Str(string) => {
             let parts = string.normalized_parts();
             let span = string.syntax().text_range();
             if parts.is_empty() {
-                Ok(Attr::Str(ctx.new_sym("".to_string()), span))
+                Ok(Attr::Str(ctx.intern_string(""), span))
             } else if parts.len() == 1 {
                 match parts.into_iter().next().expect("len checked") {
-                    Literal(ident) => Ok(Attr::Str(ctx.new_sym(ident), span)),
+                    Literal(ident) => Ok(Attr::Str(ctx.intern_string(ident), span)),
                     Interpolation(interpol) => Ok(Attr::Dynamic(
                         interpol
                             .expr()
@@ -886,7 +970,10 @@ fn downgrade_attr<'id, 'ir>(
                 let parts = parts
                     .into_iter()
                     .map(|part| match part {
-                        Literal(lit) => Ok(ctx.new_expr(Ir::Str(lit.box_in(bump)))),
+                        Literal(lit) => {
+                            let id = ctx.intern_string(lit);
+                            Ok(ctx.new_expr(Ir::Str(id)))
+                        }
                         Interpolation(interpol) => interpol
                             .expr()
                             .require(ctx, interpol.syntax().text_range())?
@@ -915,7 +1002,7 @@ fn downgrade_attr<'id, 'ir>(
 fn downgrade_attrpath<'id, 'ir>(
     attrpath: ast::Attrpath,
     ctx: &mut impl DowngradeContext<'id, 'ir>,
-) -> Result<Vec<'ir, Attr<IrRef<'id, 'ir>>>> {
+) -> Result<Vec<'ir, Attr<GhostRoIrRef<'id, 'ir>>>> {
     let bump = ctx.bump();
     attrpath
         .attrs()
@@ -924,7 +1011,7 @@ fn downgrade_attrpath<'id, 'ir>(
 }
 
 struct PatternBindings<'id, 'ir> {
-    body: IrRef<'id, 'ir>,
+    body: GhostRoIrRef<'id, 'ir>,
     required: Vec<'ir, (StringId, TextRange)>,
     optional: Vec<'ir, (StringId, TextRange)>,
 }
@@ -933,7 +1020,7 @@ fn downgrade_pattern_bindings<'id, 'ir, Ctx>(
     pat_entries: impl Iterator<Item = ast::PatEntry>,
     alias: Option<StringId>,
     ctx: &mut Ctx,
-    body_fn: impl FnOnce(&mut Ctx, &[StringId]) -> Result<IrRef<'id, 'ir>>,
+    body_fn: impl FnOnce(&mut Ctx, &[StringId]) -> Result<GhostRoIrRef<'id, 'ir>>,
 ) -> Result<PatternBindings<'id, 'ir>>
 where
     Ctx: DowngradeContext<'id, 'ir>,
@@ -951,13 +1038,13 @@ where
     for entry in pat_entries {
         let ident = entry.ident().require(ctx, entry.syntax().text_range())?;
         let sym_span = ident.syntax().text_range();
-        let sym = ctx.new_sym(ident.syntax().text().to_string());
+        let sym = ctx.intern_string(ident.syntax().text().to_string());
         let default = entry.default();
         let span = entry.syntax().text_range();
 
         if !seen_params.insert(sym) {
             return Err(Error::downgrade_error(
-                format!("duplicate parameter '{}'", ctx.get_sym(sym)),
+                format!("duplicate parameter '{}'", ctx.resolve_sym(sym)),
                 ctx.get_current_source(),
                 span,
             ));
@@ -992,6 +1079,7 @@ where
     }
 
     let arg = ctx.new_expr(Ir::Arg { layer: 0 });
+    let arg_thunk = ctx.maybe_thunk(arg);
     ctx.with_let_scope(&keys, |ctx| {
         let vals = params
             .into_iter()
@@ -1002,21 +1090,17 @@ where
                     default,
                     span,
                 } = param;
-                let default = if let Some(default) = default {
+                let default = default.map(|default| default.downgrade(ctx)).transpose()?;
-                    let default = default.clone().downgrade(ctx)?;
-                    Some(ctx.maybe_thunk(default))
-                } else {
-                    None
-                };
 
-                Ok(ctx.new_expr(Ir::Select {
+                let expr = ctx.new_expr(Ir::Select {
                     expr: arg,
                     attrpath: Vec::from_iter_in([Attr::Str(sym, sym_span)], bump),
                     default,
                     span,
-                }))
+                });
+                Ok(ctx.maybe_thunk(expr))
             })
-            .chain(alias.into_iter().map(|_| Ok(arg)))
+            .chain(alias.into_iter().map(|_| Ok(arg_thunk)))
             .collect_in::<Result<_>>(bump)?;
 
         let body = body_fn(ctx, &keys)?;
@@ -1036,10 +1120,10 @@ fn downgrade_let_bindings<'id, 'ir, Ctx, F>(
     entries: Vec<'ir, ast::Entry>,
     ctx: &mut Ctx,
     body_fn: F,
-) -> Result<IrRef<'id, 'ir>>
+) -> Result<GhostRoIrRef<'id, 'ir>>
 where
     Ctx: DowngradeContext<'id, 'ir>,
-    F: FnOnce(&mut Ctx, &[StringId]) -> Result<IrRef<'id, 'ir>>,
+    F: FnOnce(&mut Ctx, &[StringId]) -> Result<GhostRoIrRef<'id, 'ir>>,
 {
     downgrade_rec_attrs_impl::<_, _, false>(entries, ctx, |ctx, binding_keys, _dyns| {
         body_fn(ctx, binding_keys)
@@ -1049,7 +1133,7 @@ where
 fn downgrade_rec_bindings<'id, 'ir, Ctx>(
     entries: Vec<'ir, ast::Entry>,
     ctx: &mut Ctx,
-) -> Result<IrRef<'id, 'ir>>
+) -> Result<GhostRoIrRef<'id, 'ir>>
 where
     Ctx: DowngradeContext<'id, 'ir>,
 {
@@ -1070,14 +1154,18 @@ fn downgrade_rec_attrs_impl<'id, 'ir, Ctx, F, const ALLOW_DYN: bool>(
     entries: Vec<'ir, ast::Entry>,
     ctx: &mut Ctx,
     body_fn: F,
-) -> Result<IrRef<'id, 'ir>>
+) -> Result<GhostRoIrRef<'id, 'ir>>
 where
     Ctx: DowngradeContext<'id, 'ir>,
     F: FnOnce(
         &mut Ctx,
         &[StringId],
-        &[(IrRef<'id, 'ir>, IrRef<'id, 'ir>, TextRange)],
+        &[(
-    ) -> Result<IrRef<'id, 'ir>>,
+            GhostRoIrRef<'id, 'ir>,
+            GhostRoMaybeThunkRef<'id, 'ir>,
+            TextRange,
+        )],
+    ) -> Result<GhostRoIrRef<'id, 'ir>>,
 {
     let mut pending = PendingAttrSet::new_in(ctx.bump());
     pending.collect_entries(entries.iter().cloned(), ctx)?;
@@ -1089,18 +1177,21 @@ where
 
     ctx.with_let_scope(&keys, |ctx| {
         let finalized = finalize_pending_set::<_, ALLOW_DYN>(pending, &inherit_lookups, ctx)?;
-        let vals = keys
+        let vals = {
-            .iter()
+            let mut temp = Vec::with_capacity_in(keys.len(), ctx.bump());
-            .map(|sym| finalized.stcs.get(sym).expect("WTF").0)
+            for sym in &keys {
-            .collect_in(ctx.bump());
+                temp.push(finalized.stcs.get(sym).expect("WTF").0);
+            }
+            temp
+        };
         body_fn(ctx, &keys, &finalized.dyns).map(|body| (vals, body))
     })
 }
 
-fn collect_inherit_lookups<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>>(
+fn collect_inherit_lookups<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>>(
     entries: &[ast::Entry],
     ctx: &mut Ctx,
-) -> Result<HashMap<'ir, StringId, (IrRef<'id, 'ir>, TextRange)>> {
+) -> Result<HashMap<'ir, StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>> {
     let mut inherit_lookups = HashMap::new_in(ctx.bump());
     for entry in entries {
         if let ast::Entry::Inherit(inherit) = entry
@@ -1109,7 +1200,7 @@ fn collect_inherit_lookups<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>>(
             for attr in inherit.attrs() {
                 if let ast::Attr::Ident(ident) = attr {
                     let attr_span = ident.syntax().text_range();
-                    let sym = ctx.new_sym(ident.to_string());
+                    let sym = ctx.intern_string(ident.to_string());
                     let expr = ctx.lookup(sym, attr_span)?;
                     inherit_lookups.insert(sym, (expr, attr_span));
                 }
@@ -1128,7 +1219,7 @@ fn collect_binding_syms<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, const AL
     for (sym, (_, span)) in &pending.stcs {
         if !binding_syms.insert(*sym) {
             return Err(Error::downgrade_error(
-                format!("attribute '{}' already defined", ctx.get_sym(*sym)),
+                format!("attribute '{}' already defined", ctx.resolve_sym(*sym)),
                 ctx.get_current_source(),
                 *span,
             ));
@@ -1140,15 +1231,15 @@ fn collect_binding_syms<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, const AL
 
 fn finalize_pending_set<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_DYN: bool>(
     pending: PendingAttrSet,
-    inherit_lookups: &HashMap<StringId, (IrRef<'id, 'ir>, TextRange)>,
+    inherit_lookups: &HashMap<StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
     ctx: &mut Ctx,
 ) -> Result<FinalizedAttrSet<'id, 'ir>> {
     let mut stcs = HashMap::new_in(ctx.bump());
     let mut dyns = Vec::new_in(ctx.bump());
 
     for (sym, (value, value_span)) in pending.stcs {
-        let expr_id = finalize_pending_value::<_, ALLOW_DYN>(value, inherit_lookups, ctx)?;
+        let expr = finalize_pending_value::<_, ALLOW_DYN>(value, inherit_lookups, ctx)?;
-        stcs.insert(sym, (expr_id, value_span));
+        stcs.insert(sym, (ctx.maybe_thunk(expr), value_span));
     }
 
     if ALLOW_DYN {
@@ -1156,12 +1247,10 @@ fn finalize_pending_set<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_D
             let key_id = downgrade_attr(attr, ctx)?;
             let key_expr = match key_id {
                 Attr::Dynamic(id, _) => id,
-                Attr::Str(sym, _attr_span) => {
+                Attr::Str(sym, _attr_span) => ctx.new_expr(Ir::Str(sym)),
-                    ctx.new_expr(Ir::Str(ctx.get_sym(sym).to_string().box_in(ctx.bump())))
-                }
             };
-            let value_id = finalize_pending_value::<_, ALLOW_DYN>(value, inherit_lookups, ctx)?;
+            let value = finalize_pending_value::<_, ALLOW_DYN>(value, inherit_lookups, ctx)?;
-            dyns.push((key_expr, value_id, value_span));
+            dyns.push((key_expr, ctx.maybe_thunk(value), value_span));
         }
     }
 
@@ -1170,30 +1259,26 @@ fn finalize_pending_set<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_D
 
 fn finalize_pending_value<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_DYN: bool>(
     value: PendingValue,
-    inherit_lookups: &HashMap<StringId, (IrRef<'id, 'ir>, TextRange)>,
+    inherit_lookups: &HashMap<StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
     ctx: &mut Ctx,
-) -> Result<IrRef<'id, 'ir>> {
+) -> Result<GhostRoIrRef<'id, 'ir>> {
     match value {
-        PendingValue::Expr(expr) => {
+        PendingValue::Expr(expr) => expr.downgrade(ctx),
-            let id = Downgrade::downgrade(expr, ctx)?;
-            Ok(ctx.maybe_thunk(id))
-        }
         PendingValue::InheritFrom(from_expr, sym, span) => {
-            let from_id = Downgrade::downgrade(from_expr, ctx)?;
+            let from = Downgrade::downgrade(from_expr, ctx)?;
-            let select_id = ctx.new_expr(Ir::Select {
+            Ok(ctx.new_expr(Ir::Select {
-                expr: from_id,
+                expr: from,
                 attrpath: Vec::from_iter_in([Attr::Str(sym, span)], ctx.bump()),
                 default: None,
                 span,
-            });
+            }))
-            Ok(ctx.maybe_thunk(select_id))
         }
         PendingValue::InheritScope(sym, span) => {
             if let Some(&(expr, _)) = inherit_lookups.get(&sym) {
-                Ok(ctx.maybe_thunk(expr))
+                Ok(ctx.new_expr(Ir::MaybeThunk(expr)))
             } else {
-                let lookup_id = ctx.lookup(sym, span)?;
+                ctx.lookup(sym, span)
-                Ok(ctx.maybe_thunk(lookup_id))
+                    .map(|val| ctx.new_expr(Ir::MaybeThunk(val)))
             }
         }
         PendingValue::Set(set) => {
@@ -1215,15 +1300,15 @@ fn finalize_pending_value<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW
 
 fn downgrade_path<'id, 'ir>(
     parts: impl IntoIterator<Item = ast::InterpolPart<ast::PathContent>>,
-    _span: rnix::TextRange,
     ctx: &mut impl DowngradeContext<'id, 'ir>,
-) -> Result<IrRef<'id, 'ir>> {
+) -> Result<GhostRoIrRef<'id, 'ir>> {
     let bump = ctx.bump();
     let parts = parts
         .into_iter()
         .map(|part| match part {
             ast::InterpolPart::Literal(lit) => {
-                Ok(ctx.new_expr(Ir::Str(lit.text().to_string().box_in(ctx.bump()))))
+                let id = ctx.intern_string(lit.text());
+                Ok(ctx.new_expr(Ir::Str(id)))
             }
             ast::InterpolPart::Interpolation(interpol) => interpol
                 .expr()

fix-compiler/src/lib.rs

@@ -1,107 +1,26 @@
-use std::ops::Deref;
+use fix_bytecode::{Const, InstructionPtr, Op, OperandType, PrimOpPhase};
-
+use fix_lang::{BUILTINS, StringId};
-use gc_arena::Collect;
 use hashbrown::HashMap;
-use num_enum::TryFromPrimitive;
 use rnix::TextRange;
 use string_interner::Symbol as _;
 
-use crate::ir::{Attr, BinOpKind, Ir, Param, RawIrRef, StringId, ThunkId, UnOpKind};
+mod context;
-use crate::runtime::BUILTINS;
+pub mod ir;
-use crate::runtime::value::{Null, PrimOp, StaticValue};
+pub use context::{CodeState, ExtraScope};
+pub use fix_bytecode::disassembler;
+pub use ir::{Attr, BinOpKind, Ir, MaybeThunk, Param, RawIrRef, ThunkId, UnOpKind};
 
-pub struct InstructionPtr(pub(crate) usize);
+pub trait BytecodeContext {
-
-#[derive(Collect)]
-#[collect(require_static)]
-pub struct Bytecode {
-    pub code: Box<[u8]>,
-    pub current_dir: String,
-}
-
-pub(crate) trait BytecodeContext {
     fn intern_string(&mut self, s: &str) -> StringId;
     fn register_span(&mut self, range: TextRange) -> u32;
     fn get_code(&self) -> &[u8];
     fn get_code_mut(&mut self) -> &mut Vec<u8>;
-    fn add_constant(&mut self, val: crate::runtime::value::StaticValue) -> u32;
+    fn add_constant(&mut self, val: Const) -> u32;
-}
+    fn current_source_dir(&mut self) -> StringId;
-
-#[repr(u8)]
-#[derive(Debug, Clone, Copy, TryFromPrimitive)]
-#[allow(clippy::enum_variant_names)]
-pub enum Op {
-    PushSmi,
-    PushBigInt,
-    PushFloat,
-    PushString,
-    PushNull,
-    PushTrue,
-    PushFalse,
-
-    LoadLocal,
-    LoadOuter,
-    StoreLocal,
-    AllocLocals,
-
-    MakeThunk,
-    MakeClosure,
-    MakePatternClosure,
-
-    Call,
-    CallNoSpan,
-
-    MakeAttrs,
-    MakeEmptyAttrs,
-    Select,
-    SelectDefault,
-    HasAttr,
-
-    MakeList,
-    MakeEmptyList,
-
-    OpAdd,
-    OpSub,
-    OpMul,
-    OpDiv,
-    OpEq,
-    OpNeq,
-    OpLt,
-    OpGt,
-    OpLeq,
-    OpGeq,
-    OpConcat,
-    OpUpdate,
-
-    OpNeg,
-    OpNot,
-
-    JumpIfFalse,
-    JumpIfTrue,
-    Jump,
-
-    ConcatStrings,
-    ResolvePath,
-
-    Assert,
-
-    PushWith,
-    PopWith,
-    WithLookup,
-
-    LoadBuiltins,
-    LoadBuiltin,
-
-    MkPos,
-
-    LoadReplBinding,
-    LoadScopedBinding,
-
-    Return,
 }
 
 struct ScopeInfo {
-    depth: u16,
+    depth: u8,
     thunk_map: HashMap<ThunkId, u32>,
 }
 
@@ -110,22 +29,17 @@ struct BytecodeEmitter<'a, Ctx: BytecodeContext> {
     scope_stack: Vec<ScopeInfo>,
 }
 
-pub(crate) const OPERAND_CONST: u8 = 0;
+pub enum InlineOperand {
-pub(crate) const OPERAND_LOCAL: u8 = 1;
+    Const(Const),
-pub(crate) const OPERAND_BUILTINS: u8 = 2;
-pub(crate) const OPERAND_BIGINT: u8 = 3;
-
-pub(crate) const KEY_STATIC: u8 = 0;
-pub(crate) const KEY_DYNAMIC: u8 = 1;
-
-enum InlineOperand {
-    Const(StaticValue),
-    Local { layer: u16, local: u32 },
-    Builtins,
     BigInt(i64),
+    Local { layer: u8, local: u32 },
+    BuiltinConst(StringId),
+    Builtins,
+    ReplBinding(StringId),
+    ScopedImportBinding { id: StringId, slot_id: u32 },
 }
 
-pub(crate) fn compile_bytecode(ir: RawIrRef<'_>, ctx: &mut impl BytecodeContext) -> InstructionPtr {
+pub fn compile_bytecode(ir: RawIrRef<'_>, ctx: &mut impl BytecodeContext) -> InstructionPtr {
     let ip = ctx.get_code().len();
     let mut emitter = BytecodeEmitter::new(ctx);
     emitter.emit_toplevel(ir);
@@ -140,57 +54,77 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         }
     }
 
-    fn classify_value(&mut self, ir: RawIrRef<'_>) -> InlineOperand {
+    #[must_use]
-        match ir.deref() {
+    fn inline_maybe_thunk(&self, val: &MaybeThunk) -> InlineOperand {
-            &Ir::Int(x) => {
+        use MaybeThunk::*;
-                if x <= i32::MAX as i64 {
+        match *val {
-                    InlineOperand::Const(StaticValue::new_inline(x as i32))
+            Int(x) => {
+                if let Ok(x) = x.try_into() {
+                    InlineOperand::Const(Const::Smi(x))
                 } else {
                     InlineOperand::BigInt(x)
                 }
             }
-            &Ir::Float(x) => InlineOperand::Const(StaticValue::new_float(x)),
+            Float(x) => InlineOperand::Const(Const::Float(x)),
-            &Ir::Bool(b) => InlineOperand::Const(StaticValue::new_inline(b)),
+            Bool(b) => InlineOperand::Const(Const::Bool(b)),
-            Ir::Null => InlineOperand::Const(StaticValue::new_inline(Null)),
+            Null => InlineOperand::Const(Const::Null),
-            Ir::Str(s) => {
+            Str(id) => InlineOperand::Const(Const::String(id)),
-                let sid = self.ctx.intern_string(s.deref());
+            Path(id) => InlineOperand::Const(Const::String(id)),
-                InlineOperand::Const(StaticValue::new_inline(sid))
+            Thunk(id) => {
-            }
-            &Ir::Thunk(id) => {
                 let (layer, local) = self.resolve_thunk(id);
                 InlineOperand::Local { layer, local }
             }
-            &Ir::Arg { layer } => InlineOperand::Local {
+            Arg { layer } => InlineOperand::Local { layer, local: 0 },
-                layer: layer.try_into().expect("scope too deep!"),
+            Builtin(id) => {
-                local: 0,
+                let (_, arity) = BUILTINS[id as usize];
-            },
+                InlineOperand::Const(Const::PrimOp {
-            &Ir::Builtin(id) => {
+                    id,
-                let arity = BUILTINS[id as usize].1;
+                    arity,
-                InlineOperand::Const(StaticValue::new_inline(PrimOp { id, arity }))
+                    dispatch_ip: PrimOpPhase::entry_for_builtin(id).ip(),
+                })
+            }
+            BuiltinConst(id) => InlineOperand::BuiltinConst(id),
+            Builtins => InlineOperand::Builtins,
+            ReplBinding(id) => InlineOperand::ReplBinding(id),
+            ScopedImportBinding { slot_id, sym: id } => {
+                InlineOperand::ScopedImportBinding { slot_id, id }
             }
-            Ir::Builtins => InlineOperand::Builtins,
-            _ => panic!("cannot classify IR node as inline operand"),
         }
     }
 
-    fn emit_inline_operand(&mut self, operand: InlineOperand) {
+    fn emit_maybe_thunk(&mut self, val: &MaybeThunk) {
+        use InlineOperand::*;
+        let operand = self.inline_maybe_thunk(val);
         match operand {
-            InlineOperand::Const(val) => {
+            Const(val) => {
                 let idx = self.ctx.add_constant(val);
-                self.emit_u8(OPERAND_CONST);
+                self.emit_u8(OperandType::Const as u8);
                 self.emit_u32(idx);
             }
-            InlineOperand::Local { layer, local } => {
+            BigInt(val) => {
-                self.emit_u8(OPERAND_LOCAL);
+                self.emit_u8(OperandType::BigInt as u8);
-                self.emit_u8(layer as u8);
+                self.emit_i64(val);
+            }
+            Local { layer, local } => {
+                self.emit_u8(OperandType::Local as u8);
+                self.emit_u8(layer);
                 self.emit_u32(local);
             }
-            InlineOperand::Builtins => {
+            BuiltinConst(id) => {
-                self.emit_u8(OPERAND_BUILTINS);
+                self.emit_u8(OperandType::BuiltinConst as u8);
+                self.emit_str_id(id);
             }
-            InlineOperand::BigInt(val) => {
+            Builtins => {
-                self.emit_u8(OPERAND_BIGINT);
+                self.emit_u8(OperandType::Builtins as u8);
-                self.emit_i64(val);
+            }
+            ReplBinding(id) => {
+                self.emit_u8(OperandType::ReplBinding as u8);
+                self.emit_str_id(id);
+            }
+            ScopedImportBinding { id, slot_id } => {
+                self.emit_u8(OperandType::ScopedImportBinding as u8);
+                self.emit_u32(slot_id);
+                self.emit_str_id(id);
             }
         }
     }
@@ -200,6 +134,11 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         self.ctx.get_code_mut().push(op as u8);
     }
 
+    #[inline]
+    fn emit_bool(&mut self, val: bool) {
+        self.emit_u8(u8::from(val));
+    }
+
     #[inline]
     fn emit_u8(&mut self, val: u8) {
         self.ctx.get_code_mut().push(val);
@@ -271,11 +210,11 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             .extend_from_slice(&(id.0.to_usize() as u32).to_le_bytes());
     }
 
-    fn current_depth(&self) -> u16 {
+    fn current_depth(&self) -> u8 {
         self.scope_stack.last().map_or(0, |s| s.depth)
     }
 
-    fn resolve_thunk(&self, id: ThunkId) -> (u16, u32) {
+    fn resolve_thunk(&self, id: ThunkId) -> (u8, u32) {
         for scope in self.scope_stack.iter().rev() {
             if let Some(&local_idx) = scope.thunk_map.get(&id) {
                 let layer = self.current_depth() - scope.depth;
@@ -285,145 +224,19 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         panic!("ThunkId {:?} not found in any scope", id);
     }
 
-    fn emit_load(&mut self, layer: u16, local: u32) {
+    fn emit_load(&mut self, layer: u8, local: u32) {
         if layer == 0 {
             self.emit_op(Op::LoadLocal);
             self.emit_u32(local);
         } else {
             self.emit_op(Op::LoadOuter);
-            self.emit_u8(layer as u8);
+            self.emit_u8(layer);
             self.emit_u32(local);
         }
     }
 
-    fn count_with_thunks(&self, ir: RawIrRef<'_>) -> usize {
-        match ir.deref() {
-            Ir::With { thunks, body, .. } => thunks.len() + self.count_with_thunks(*body),
-            Ir::TopLevel { thunks, body } => thunks.len() + self.count_with_thunks(*body),
-            Ir::If { cond, consq, alter } => {
-                self.count_with_thunks(*cond)
-                    + self.count_with_thunks(*consq)
-                    + self.count_with_thunks(*alter)
-            }
-            Ir::BinOp { lhs, rhs, .. } => {
-                self.count_with_thunks(*lhs) + self.count_with_thunks(*rhs)
-            }
-            Ir::UnOp { rhs, .. } => self.count_with_thunks(*rhs),
-            Ir::Call { func, arg, .. } => {
-                self.count_with_thunks(*func) + self.count_with_thunks(*arg)
-            }
-            Ir::Assert {
-                assertion, expr, ..
-            } => self.count_with_thunks(*assertion) + self.count_with_thunks(*expr),
-            Ir::Select { expr, default, .. } => {
-                self.count_with_thunks(*expr) + default.map_or(0, |d| self.count_with_thunks(d))
-            }
-            Ir::HasAttr { lhs, .. } => self.count_with_thunks(*lhs),
-            Ir::ConcatStrings { parts, .. } => {
-                parts.iter().map(|p| self.count_with_thunks(*p)).sum()
-            }
-            Ir::Path(p) => self.count_with_thunks(*p),
-            Ir::List { items } => items.iter().map(|item| self.count_with_thunks(*item)).sum(),
-            Ir::AttrSet { stcs, dyns } => {
-                stcs.iter()
-                    .map(|(_, &(val, _))| self.count_with_thunks(val))
-                    .sum::<usize>()
-                    + dyns
-                        .iter()
-                        .map(|&(k, v, _)| self.count_with_thunks(k) + self.count_with_thunks(v))
-                        .sum::<usize>()
-            }
-            _ => 0,
-        }
-    }
-
-    fn collect_all_thunks<'ir>(
-        &self,
-        own_thunks: &[(ThunkId, RawIrRef<'ir>)],
-        body: RawIrRef<'ir>,
-    ) -> Vec<(ThunkId, RawIrRef<'ir>)> {
-        let mut all = Vec::from(own_thunks);
-        self.collect_with_thunks_recursive(body, &mut all);
-        let mut i = 0;
-        while i < all.len() {
-            let thunk_body = all[i].1;
-            self.collect_with_thunks_recursive(thunk_body, &mut all);
-            i += 1;
-        }
-        all
-    }
-
-    fn collect_with_thunks_recursive<'ir>(
-        &self,
-        ir: RawIrRef<'ir>,
-        out: &mut Vec<(ThunkId, RawIrRef<'ir>)>,
-    ) {
-        match ir.deref() {
-            Ir::With { thunks, body, .. } => {
-                for &(id, inner) in thunks.iter() {
-                    out.push((id, inner));
-                }
-                self.collect_with_thunks_recursive(*body, out);
-            }
-            Ir::TopLevel { thunks, body } => {
-                for &(id, inner) in thunks.iter() {
-                    out.push((id, inner));
-                }
-                self.collect_with_thunks_recursive(*body, out);
-            }
-            Ir::If { cond, consq, alter } => {
-                self.collect_with_thunks_recursive(*cond, out);
-                self.collect_with_thunks_recursive(*consq, out);
-                self.collect_with_thunks_recursive(*alter, out);
-            }
-            Ir::BinOp { lhs, rhs, .. } => {
-                self.collect_with_thunks_recursive(*lhs, out);
-                self.collect_with_thunks_recursive(*rhs, out);
-            }
-            Ir::UnOp { rhs, .. } => self.collect_with_thunks_recursive(*rhs, out),
-            Ir::Call { func, arg, .. } => {
-                self.collect_with_thunks_recursive(*func, out);
-                self.collect_with_thunks_recursive(*arg, out);
-            }
-            Ir::Assert {
-                assertion, expr, ..
-            } => {
-                self.collect_with_thunks_recursive(*assertion, out);
-                self.collect_with_thunks_recursive(*expr, out);
-            }
-            Ir::Select { expr, default, .. } => {
-                self.collect_with_thunks_recursive(*expr, out);
-                if let Some(d) = default {
-                    self.collect_with_thunks_recursive(*d, out);
-                }
-            }
-            Ir::HasAttr { lhs, .. } => self.collect_with_thunks_recursive(*lhs, out),
-            Ir::ConcatStrings { parts, .. } => {
-                for p in parts.iter() {
-                    self.collect_with_thunks_recursive(*p, out);
-                }
-            }
-            Ir::Path(p) => self.collect_with_thunks_recursive(*p, out),
-            Ir::List { items } => {
-                for item in items.iter() {
-                    self.collect_with_thunks_recursive(*item, out);
-                }
-            }
-            Ir::AttrSet { stcs, dyns } => {
-                for (_, &(val, _)) in stcs.iter() {
-                    self.collect_with_thunks_recursive(val, out);
-                }
-                for &(key, val, _) in dyns.iter() {
-                    self.collect_with_thunks_recursive(key, out);
-                    self.collect_with_thunks_recursive(val, out);
-                }
-            }
-            _ => {}
-        }
-    }
-
     fn push_scope(&mut self, has_arg: bool, thunk_ids: &[ThunkId]) {
-        let depth = self.scope_stack.len() as u16;
+        let depth = self.scope_stack.len().try_into().expect("scope too deep!");
         let thunk_base = if has_arg { 1u32 } else { 0u32 };
         let thunk_map = thunk_ids
             .iter()
@@ -438,19 +251,13 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
     }
 
     fn emit_toplevel(&mut self, ir: RawIrRef<'_>) {
-        match ir.deref() {
+        match ir {
             &Ir::TopLevel { body, ref thunks } => {
-                let with_thunk_count = self.count_with_thunks(body);
+                let thunk_ids: Vec<ThunkId> = thunks.iter().map(|&(id, _)| id).collect();
-                let total_slots = thunks.len() + with_thunk_count;
-
-                let all_thunks = self.collect_all_thunks(thunks, body);
-                let thunk_ids: Vec<ThunkId> = all_thunks.iter().map(|&(id, _)| id).collect();
-
                 self.push_scope(false, &thunk_ids);
-
+                if !thunks.is_empty() {
-                if total_slots > 0 {
                     self.emit_op(Op::AllocLocals);
-                    self.emit_u32(total_slots as u32);
+                    self.emit_u32(thunks.len().try_into().expect("too many thunks"));
                 }
 
                 self.emit_scope_thunks(thunks);
@@ -484,11 +291,11 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
     }
 
     fn emit_expr(&mut self, ir: RawIrRef<'_>) {
-        match ir.deref() {
+        match ir {
             &Ir::Int(x) => {
-                if x <= i32::MAX as i64 {
+                if let Ok(x) = x.try_into() {
                     self.emit_op(Op::PushSmi);
-                    self.emit_i32(x as i32);
+                    self.emit_i32(x);
                 } else {
                     self.emit_op(Op::PushBigInt);
                     self.emit_i64(x);
@@ -501,14 +308,15 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             &Ir::Bool(true) => self.emit_op(Op::PushTrue),
             &Ir::Bool(false) => self.emit_op(Op::PushFalse),
             Ir::Null => self.emit_op(Op::PushNull),
-            Ir::Str(s) => {
+            &Ir::Str(id) => {
-                let idx = self.ctx.intern_string(s.deref());
                 self.emit_op(Op::PushString);
-                self.emit_str_id(idx);
+                self.emit_str_id(id);
             }
             &Ir::Path(p) => {
                 self.emit_expr(p);
                 self.emit_op(Op::ResolvePath);
+                let dir_id = self.ctx.current_source_dir();
+                self.emit_str_id(dir_id);
             }
             &Ir::If { cond, consq, alter } => {
                 self.emit_expr(cond);
@@ -561,20 +369,17 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
                     self.emit_op(Op::MakeList);
                     self.emit_u32(items.len() as u32);
                     for &item in items.iter() {
-                        let operand = self.classify_value(item);
+                        self.emit_maybe_thunk(item);
-                        self.emit_inline_operand(operand);
                     }
                 }
             }
-            &Ir::Call { func, arg, span } => {
+            &Ir::Call { func, arg, .. } => {
-                self.emit_expr(arg);
                 self.emit_expr(func);
-                let span_id = self.ctx.register_span(span);
                 self.emit_op(Op::Call);
-                self.emit_u32(span_id);
+                self.emit_maybe_thunk(arg);
             }
             &Ir::Arg { layer } => {
-                self.emit_load(layer.try_into().expect("scope too deep!"), 0);
+                self.emit_load(layer, 0);
             }
             &Ir::TopLevel { body, ref thunks } => {
                 self.emit_toplevel_inner(body, thunks);
@@ -587,10 +392,6 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             } => {
                 self.emit_select(expr, attrpath, default, span);
             }
-            &Ir::Thunk(id) => {
-                let (layer, local) = self.resolve_thunk(id);
-                self.emit_load(layer, local);
-            }
             Ir::Builtins => {
                 self.emit_op(Op::LoadBuiltins);
             }
@@ -600,7 +401,7 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             }
             &Ir::BuiltinConst(id) => {
                 self.emit_select(
-                    RawIrRef(&Ir::Builtins),
+                    &Ir::Builtins,
                     &[Attr::Str(id, TextRange::default())],
                     None,
                     TextRange::default(),
@@ -610,13 +411,13 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
                 ref parts,
                 force_string,
             } => {
+                for &part in parts.iter() {
+                    self.emit_expr(part);
+                    self.emit_op(Op::CoerceToString);
+                }
                 self.emit_op(Op::ConcatStrings);
                 self.emit_u16(parts.len() as u16);
-                self.emit_u8(if force_string { 1 } else { 0 });
+                self.emit_bool(force_string);
-                for &part in parts.iter() {
-                    let operand = self.classify_value(part);
-                    self.emit_inline_operand(operand);
-                }
             }
             &Ir::HasAttr { lhs, ref rhs } => {
                 self.emit_has_attr(lhs, rhs);
@@ -630,34 +431,91 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
                 let raw_idx = self.ctx.intern_string(assertion_raw);
                 let span_id = self.ctx.register_span(*span);
                 self.emit_expr(*assertion);
-                self.emit_expr(*expr);
                 self.emit_op(Op::Assert);
                 self.emit_str_id(raw_idx);
                 self.emit_u32(span_id);
-            }
+                self.emit_expr(*expr);
-            &Ir::CurPos(span) => {
-                let span_id = self.ctx.register_span(span);
-                self.emit_op(Op::MkPos);
-                self.emit_u32(span_id);
             }
             &Ir::ReplBinding(name) => {
                 self.emit_op(Op::LoadReplBinding);
                 self.emit_str_id(name);
             }
-            &Ir::ScopedImportBinding(name) => {
+            &Ir::ScopedImportBinding { sym, slot_id } => {
                 self.emit_op(Op::LoadScopedBinding);
-                self.emit_str_id(name);
+                self.emit_u32(slot_id);
+                self.emit_str_id(sym);
             }
-            &Ir::With {
+            Ir::WithLookup { sym, namespaces } => {
-                namespace,
+                // counter
-                body,
+                self.emit_expr(&Ir::Int(0));
-                ref thunks,
+                self.emit_op(Op::LookupWith);
-            } => {
+                self.emit_str_id(*sym);
-                self.emit_with(namespace, body, thunks);
+                self.emit_u8(
+                    namespaces
+                        .len()
+                        .try_into()
+                        .expect("too many `with` namespaces"),
+                );
+                for namespace in namespaces {
+                    self.emit_maybe_thunk(namespace);
+                }
             }
-            &Ir::WithLookup(name) => {
+            &Ir::MaybeThunk(thunk) => {
-                self.emit_op(Op::WithLookup);
+                use MaybeThunk::*;
-                self.emit_str_id(name);
+                match *thunk {
+                    Int(x) => {
+                        if let Ok(x) = x.try_into() {
+                            self.emit_op(Op::PushSmi);
+                            self.emit_i32(x);
+                        } else {
+                            self.emit_op(Op::PushBigInt);
+                            self.emit_i64(x);
+                        }
+                    }
+                    Float(x) => {
+                        self.emit_op(Op::PushFloat);
+                        self.emit_f64(x);
+                    }
+                    Bool(true) => self.emit_op(Op::PushTrue),
+                    Bool(false) => self.emit_op(Op::PushFalse),
+                    Null => self.emit_op(Op::PushNull),
+                    Str(id) => {
+                        self.emit_op(Op::PushString);
+                        self.emit_str_id(id);
+                    }
+                    Path(id) => {
+                        self.emit_op(Op::PushString);
+                        self.emit_str_id(id);
+                        self.emit_op(Op::ResolvePath);
+                        let dir_id = self.ctx.current_source_dir();
+                        self.emit_str_id(dir_id);
+                    }
+                    Thunk(id) => {
+                        let (layer, local) = self.resolve_thunk(id);
+                        self.emit_load(layer, local);
+                    }
+                    Arg { layer } => self.emit_load(layer, 0),
+                    Builtin(id) => {
+                        self.emit_op(Op::LoadBuiltin);
+                        self.emit_u8(id as u8);
+                    }
+                    BuiltinConst(id) => self.emit_select(
+                        &Ir::Builtins,
+                        &[Attr::Str(id, TextRange::default())],
+                        None,
+                        TextRange::default(),
+                    ),
+                    Builtins => self.emit_op(Op::LoadBuiltins),
+                    ReplBinding(name) => {
+                        self.emit_op(Op::LoadReplBinding);
+                        self.emit_str_id(name);
+                    }
+                    ScopedImportBinding { slot_id, sym } => {
+                        self.emit_op(Op::LoadScopedBinding);
+                        self.emit_u32(slot_id);
+                        self.emit_str_id(sym);
+                    }
+                }
             }
         }
     }
@@ -722,16 +580,6 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
                 let end_offset = (self.ctx.get_code_mut().len() as i32) - (after_jump as i32);
                 self.patch_i32(end_placeholder, end_offset);
             }
-            PipeL => {
-                self.emit_expr(rhs);
-                self.emit_expr(lhs);
-                self.emit_op(Op::CallNoSpan);
-            }
-            PipeR => {
-                self.emit_expr(lhs);
-                self.emit_expr(rhs);
-                self.emit_op(Op::CallNoSpan);
-            }
             _ => {
                 self.emit_expr(lhs);
                 self.emit_expr(rhs);
@@ -754,17 +602,13 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         }
     }
 
-    fn emit_func(
+    fn emit_func<'ir>(
         &mut self,
-        thunks: &[(ThunkId, RawIrRef<'_>)],
+        thunks: &[(ThunkId, RawIrRef<'ir>)],
-        param: &Option<Param<'_>>,
+        param: &Option<Param<'ir>>,
-        body: RawIrRef<'_>,
+        body: RawIrRef<'ir>,
     ) {
-        let with_thunk_count = self.count_with_thunks(body);
+        let thunk_ids: Vec<ThunkId> = thunks.iter().map(|&(id, _)| id).collect();
-        let total_slots = thunks.len() + with_thunk_count;
-
-        let all_thunks = self.collect_all_thunks(thunks, body);
-        let thunk_ids: Vec<ThunkId> = all_thunks.iter().map(|&(id, _)| id).collect();
 
         let skip_patch = self.emit_jump_placeholder();
         let entry_point = self.ctx.get_code().len() as u32;
@@ -783,10 +627,10 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         {
             self.emit_op(Op::MakePatternClosure);
             self.emit_u32(entry_point);
-            self.emit_u32(total_slots as u32);
+            self.emit_u32(thunks.len().try_into().expect("too many thunks"));
             self.emit_u16(required.len() as u16);
             self.emit_u16(optional.len() as u16);
-            self.emit_u8(if *ellipsis { 1 } else { 0 });
+            self.emit_bool(*ellipsis);
 
             for &(sym, _) in required.iter() {
                 self.emit_str_id(sym);
@@ -802,38 +646,37 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         } else {
             self.emit_op(Op::MakeClosure);
             self.emit_u32(entry_point);
-            self.emit_u32(total_slots as u32);
+            self.emit_u32(thunks.len().try_into().expect("too many thunks"));
         }
     }
 
     fn emit_attrset(
         &mut self,
-        stcs: &crate::ir::HashMap<'_, StringId, (RawIrRef<'_>, TextRange)>,
+        stcs: &ir::HashMap<'_, StringId, (&MaybeThunk, TextRange)>,
-        dyns: &[(RawIrRef<'_>, RawIrRef<'_>, TextRange)],
+        dyns: &[(RawIrRef<'_>, &MaybeThunk, TextRange)],
     ) {
         if stcs.is_empty() && dyns.is_empty() {
             self.emit_op(Op::MakeEmptyAttrs);
             return;
         }
 
-        let total = stcs.len() + dyns.len();
+        for &(key_expr, _val, _span) in dyns.iter() {
+            self.emit_expr(key_expr);
+        }
+
         self.emit_op(Op::MakeAttrs);
-        self.emit_u32(total as u32);
+        self.emit_u32(stcs.len() as u32);
+        self.emit_u32(dyns.len() as u32);
 
         for (&sym, &(val, span)) in stcs.iter() {
-            self.emit_u8(KEY_STATIC);
             self.emit_str_id(sym);
-            let val_operand = self.classify_value(val);
+            self.emit_maybe_thunk(val);
-            self.emit_inline_operand(val_operand);
             let span_id = self.ctx.register_span(span);
             self.emit_u32(span_id);
         }
-        for &(key, val, span) in dyns.iter() {
+
-            self.emit_u8(KEY_DYNAMIC);
+        for &(_key, val, span) in dyns.iter() {
-            let key_operand = self.classify_value(key);
+            self.emit_maybe_thunk(val);
-            self.emit_inline_operand(key_operand);
-            let val_operand = self.classify_value(val);
-            self.emit_inline_operand(val_operand);
             let span_id = self.ctx.register_span(span);
             self.emit_u32(span_id);
         }
@@ -847,69 +690,87 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         span: TextRange,
     ) {
         self.emit_expr(expr);
-        for attr in attrpath.iter() {
+
-            if let Attr::Dynamic(expr, _) = *attr {
+        let mut dynamic_patches = Vec::new();
-                self.emit_expr(expr);
-            }
-        }
-        if let Some(default) = default {
-            self.emit_expr(default);
-            let span_id = self.ctx.register_span(span);
-            self.emit_op(Op::SelectDefault);
-            self.emit_u16(attrpath.len() as u16);
-            self.emit_u32(span_id);
-        } else {
-            let span_id = self.ctx.register_span(span);
-            self.emit_op(Op::Select);
-            self.emit_u16(attrpath.len() as u16);
-            self.emit_u32(span_id);
-        }
         for attr in attrpath.iter() {
             match *attr {
                 Attr::Str(sym, _) => {
-                    self.emit_u8(KEY_STATIC);
+                    let span_id = self.ctx.register_span(span);
+                    self.emit_op(Op::SelectStatic);
+                    self.emit_u32(span_id);
                     self.emit_str_id(sym);
                 }
-                Attr::Dynamic(_, _) => {
+                Attr::Dynamic(key_expr, _) => {
-                    self.emit_u8(KEY_DYNAMIC);
+                    self.emit_op(Op::JumpIfSelectFailed);
+                    dynamic_patches.push(self.emit_i32_placeholder());
+                    self.emit_expr(key_expr);
+                    let span_id = self.ctx.register_span(span);
+                    self.emit_op(Op::SelectDynamic);
+                    self.emit_u32(span_id);
                 }
             }
         }
+
+        if let Some(default) = default {
+            let before: i32 = self.ctx.get_code().len().try_into().unwrap();
+            for patch in dynamic_patches {
+                self.patch_jump_target(patch);
+            }
+            self.emit_op(Op::JumpIfSelectSucceeded);
+            let placeholder = self.emit_i32_placeholder();
+            self.emit_expr(default);
+            let after: i32 = self.ctx.get_code().len().try_into().unwrap();
+            // Offset is relative to after the placeholder, so subtract the
+            // size of JumpIfSelectSucceeded (1) + placeholder (4).
+            self.patch_i32(placeholder, after - before - 5);
+        } else {
+            for patch in dynamic_patches {
+                self.patch_jump_target(patch);
+            }
+        }
     }
 
     fn emit_has_attr(&mut self, lhs: RawIrRef<'_>, rhs: &[Attr<RawIrRef<'_>>]) {
         self.emit_expr(lhs);
-        for attr in rhs.iter() {
+
-            if let Attr::Dynamic(expr, _) = *attr {
+        let mut dynamic_patches = Vec::new();
-                self.emit_expr(expr);
+        let [attrs @ .., last] = rhs else {
-            }
+            panic!("attrpath is empty");
-        }
+        };
-        self.emit_op(Op::HasAttr);
+        for attr in attrs {
-        self.emit_u16(rhs.len() as u16);
-        for attr in rhs.iter() {
             match *attr {
-                Attr::Str(sym, _) => {
+                Attr::Str(sym, span) => {
-                    self.emit_u8(KEY_STATIC);
+                    let span_id = self.ctx.register_span(span);
+                    self.emit_op(Op::HasAttrPathStatic);
+                    self.emit_u32(span_id);
                     self.emit_str_id(sym);
                 }
-                Attr::Dynamic(_, _) => {
+                Attr::Dynamic(key_expr, span) => {
-                    self.emit_u8(KEY_DYNAMIC);
+                    self.emit_op(Op::JumpIfSelectFailed);
+                    dynamic_patches.push(self.emit_i32_placeholder());
+                    self.emit_expr(key_expr);
+                    let span_id = self.ctx.register_span(span);
+                    self.emit_op(Op::HasAttrPathDynamic);
+                    self.emit_u32(span_id);
                 }
             }
         }
-    }
+        match *last {
-
+            Attr::Str(sym, _) => {
-    fn emit_with(
+                self.emit_op(Op::HasAttrStatic);
-        &mut self,
+                self.emit_str_id(sym);
-        namespace: RawIrRef<'_>,
+            }
-        body: RawIrRef<'_>,
+            Attr::Dynamic(key_expr, _) => {
-        thunks: &[(ThunkId, RawIrRef<'_>)],
+                self.emit_op(Op::JumpIfSelectFailed);
-    ) {
+                dynamic_patches.push(self.emit_i32_placeholder());
-        self.emit_expr(namespace);
+                self.emit_expr(key_expr);
-        self.emit_op(Op::PushWith);
+                self.emit_op(Op::HasAttrDynamic);
-        self.emit_scope_thunks(thunks);
+            }
-        self.emit_expr(body);
+        }
-        self.emit_op(Op::PopWith);
+        for patch in dynamic_patches {
+            self.patch_jump_target(patch);
+        }
+        self.emit_op(Op::HasAttrResolve);
     }
 
     fn emit_toplevel_inner(&mut self, body: RawIrRef<'_>, thunks: &[(ThunkId, RawIrRef<'_>)]) {

fix-error/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "fix-error"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+miette = { version = "7.6", features = ["fancy"] }
+rnix = { workspace = true }
+thiserror = "2.0"

fix-error/src/lib.rs

@@ -0,0 +1,223 @@
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+
+use miette::{Diagnostic, NamedSource, SourceSpan};
+use thiserror::Error;
+
+pub type Result<T> = core::result::Result<T, Box<Error>>;
+
+#[derive(Clone, Debug)]
+pub enum SourceType {
+    /// dir
+    Eval(Arc<PathBuf>),
+    /// dir
+    Repl(Arc<PathBuf>),
+    /// file
+    File(Arc<PathBuf>),
+    /// virtual (name, no path)
+    Virtual(Arc<str>),
+}
+
+#[derive(Clone, Debug)]
+pub struct Source {
+    pub ty: SourceType,
+    pub src: Arc<str>,
+}
+
+impl TryFrom<&str> for Source {
+    type Error = Box<Error>;
+    fn try_from(value: &str) -> Result<Self> {
+        Source::new_eval(value.into())
+    }
+}
+
+impl From<Source> for NamedSource<Arc<str>> {
+    fn from(value: Source) -> Self {
+        let name = value.get_name();
+        NamedSource::new(name, value.src.clone())
+    }
+}
+
+impl Source {
+    pub fn new_file(path: PathBuf) -> std::io::Result<Self> {
+        Ok(Source {
+            src: std::fs::read_to_string(&path)?.into(),
+            ty: SourceType::File(Arc::new(path)),
+        })
+    }
+
+    pub fn new_eval(src: String) -> Result<Self> {
+        Ok(Self {
+            ty: std::env::current_dir()
+                .map_err(|err| Error::internal(format!("Failed to get current working dir: {err}")))
+                .map(Arc::new)
+                .map(SourceType::Eval)?,
+            src: src.into(),
+        })
+    }
+
+    pub fn new_repl(src: String) -> Result<Self> {
+        Ok(Self {
+            ty: std::env::current_dir()
+                .map_err(|err| Error::internal(format!("Failed to get current working dir: {err}")))
+                .map(Arc::new)
+                .map(SourceType::Repl)?,
+            src: src.into(),
+        })
+    }
+
+    pub fn new_virtual(name: Arc<str>, src: String) -> Self {
+        Self {
+            ty: SourceType::Virtual(name),
+            src: src.into(),
+        }
+    }
+
+    pub fn get_dir(&self) -> &Path {
+        use SourceType::*;
+        match &self.ty {
+            Eval(dir) | Repl(dir) => dir.as_ref(),
+            File(file) => file
+                .as_path()
+                .parent()
+                .expect("source file must have a parent dir"),
+            Virtual(_) => Path::new("/"),
+        }
+    }
+
+    pub fn get_name(&self) -> String {
+        match &self.ty {
+            SourceType::Eval(_) => "«eval»".into(),
+            SourceType::Repl(_) => "«repl»".into(),
+            SourceType::File(path) => path.as_os_str().to_string_lossy().to_string(),
+            SourceType::Virtual(name) => name.to_string(),
+        }
+    }
+}
+
+#[derive(Error, Debug, Diagnostic)]
+pub enum Error {
+    #[error("Parse error: {message}")]
+    #[diagnostic(code(nix::parse))]
+    ParseError {
+        #[source_code]
+        src: Option<NamedSource<Arc<str>>>,
+        #[label("error occurred here")]
+        span: Option<SourceSpan>,
+        message: String,
+    },
+
+    #[error("Downgrade error: {message}")]
+    #[diagnostic(code(nix::downgrade))]
+    DowngradeError {
+        #[source_code]
+        src: Option<NamedSource<Arc<str>>>,
+        #[label("{message}")]
+        span: Option<SourceSpan>,
+        message: String,
+    },
+
+    #[error("Evaluation error: {message}")]
+    #[diagnostic(code(nix::eval))]
+    EvalError {
+        #[source_code]
+        src: Option<NamedSource<Arc<str>>>,
+        #[label("error occurred here")]
+        span: Option<SourceSpan>,
+        message: String,
+        #[related]
+        stack_trace: Vec<StackFrame>,
+    },
+
+    #[error("Internal error: {message}")]
+    #[diagnostic(code(nix::internal))]
+    InternalError { message: String },
+
+    #[error("{message}")]
+    #[diagnostic(code(nix::catchable))]
+    Catchable { message: String },
+
+    #[error("Unknown error")]
+    #[diagnostic(code(nix::unknown))]
+    Unknown,
+}
+
+impl Error {
+    pub fn parse_error(msg: String) -> Box<Self> {
+        Error::ParseError {
+            src: None,
+            span: None,
+            message: msg,
+        }
+        .into()
+    }
+
+    pub fn downgrade_error(msg: String, src: Source, span: rnix::TextRange) -> Box<Self> {
+        Error::DowngradeError {
+            src: Some(src.into()),
+            span: Some(text_range_to_source_span(span)),
+            message: msg,
+        }
+        .into()
+    }
+
+    pub fn eval_error(msg: impl Into<String>) -> Box<Self> {
+        Error::EvalError {
+            src: None,
+            span: None,
+            message: msg.into(),
+            stack_trace: Vec::new(),
+        }
+        .into()
+    }
+
+    pub fn internal(msg: String) -> Box<Self> {
+        Error::InternalError { message: msg }.into()
+    }
+
+    pub fn catchable(msg: String) -> Box<Self> {
+        Error::Catchable { message: msg }.into()
+    }
+
+    pub fn with_span(mut self: Box<Self>, span: rnix::TextRange) -> Box<Self> {
+        use Error::*;
+        let source_span = Some(text_range_to_source_span(span));
+        let (ParseError { span, .. } | DowngradeError { span, .. } | EvalError { span, .. }) =
+            self.as_mut()
+        else {
+            return self;
+        };
+        *span = source_span;
+        self
+    }
+
+    pub fn with_source(mut self: Box<Self>, source: Source) -> Box<Self> {
+        use Error::*;
+        let new_src = Some(source.into());
+        let (ParseError { src, .. } | DowngradeError { src, .. } | EvalError { src, .. }) =
+            self.as_mut()
+        else {
+            return self;
+        };
+        *src = new_src;
+        self
+    }
+}
+
+pub fn text_range_to_source_span(range: rnix::TextRange) -> SourceSpan {
+    let start = usize::from(range.start());
+    let len = usize::from(range.end()) - start;
+    SourceSpan::new(start.into(), len)
+}
+
+/// Stack frame types from Nix evaluation
+#[derive(Debug, Clone, Error, Diagnostic)]
+#[error("{message}")]
+pub struct StackFrame {
+    #[label]
+    pub span: SourceSpan,
+    #[help]
+    pub message: String,
+    #[source_code]
+    pub src: NamedSource<Arc<str>>,
+}

fix-lang/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "fix-lang"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+ere = { workspace = true }
+gc-arena = { workspace = true }
+num_enum = { workspace = true }
+string-interner = { workspace = true }

fix-lang/src/lib.rs

@@ -1,14 +1,139 @@
-use core::fmt::{Debug, Display, Formatter, Result as FmtResult};
-use core::hash::Hash;
-use core::ops::Deref;
 use std::borrow::Cow;
 use std::collections::BTreeMap;
-use std::ops::DerefMut;
+use std::fmt::{Debug, Display, Formatter, Result as FmtResult};
+use std::ops::{Deref, DerefMut};
 
-use derive_more::{Constructor, IsVariant, Unwrap};
+use gc_arena::Collect;
+use num_enum::TryFromPrimitive;
+
+macro_rules! define_builtins {
+    ($(($name:literal, $variant:ident, $arity:expr)),* $(,)?) => {
+        pub const BUILTINS: &[(&str, u8)] = &[
+            $(($name, $arity),)*
+        ];
+
+        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, TryFromPrimitive, Collect)]
+        #[repr(u8)]
+        #[collect(require_static)]
+        pub enum BuiltinId {
+            $($variant,)*
+        }
+    };
+}
+
+define_builtins! {
+    ("abort",                    Abort,                    1),
+    ("__add",                      Add,                      2),
+    ("__addErrorContext",          AddErrorContext,           2),
+    ("__all",                      All,                      2),
+    ("__any",                      Any,                      2),
+    ("__appendContext",            AppendContext,             2),
+    ("__attrNames",                AttrNames,                1),
+    ("__attrValues",               AttrValues,               1),
+    ("baseNameOf",               BaseNameOf,               1),
+    ("__bitAnd",                   BitAnd,                   2),
+    ("__bitOr",                    BitOr,                    2),
+    ("__bitXor",                   BitXor,                   2),
+    ("break",                    Break,                    1),
+    ("__catAttrs",                 CatAttrs,                 2),
+    ("__ceil",                     Ceil,                     1),
+    ("__compareVersions",          CompareVersions,          2),
+    ("__concatLists",              ConcatLists,              1),
+    ("__concatMap",                ConcatMap,                2),
+    ("__concatStringsSep",         ConcatStringsSep,         2),
+    ("__convertHash",              ConvertHash,              1),
+    ("__deepSeq",                  DeepSeq,                  2),
+    ("derivation",               Derivation,               1),
+    ("derivationStrict",         DerivationStrict,         1),
+    ("dirOf",                    DirOf,                    1),
+    ("__div",                      Div,                      2),
+    ("__elem",                     Elem,                     2),
+    ("__elemAt",                   ElemAt,                   2),
+    ("fetchGit",                 FetchGit,                 1),
+    ("fetchMercurial",           FetchMercurial,           1),
+    ("fetchTarball",             FetchTarball,             1),
+    ("fetchTree",                FetchTree,                1),
+    ("__fetchurl",                 FetchUrl,                 1),
+    ("__filter",                   Filter,                   2),
+    ("__filterSource",             FilterSource,             2),
+    ("__findFile",                 FindFile,                 2),
+    ("__floor",                    Floor,                    1),
+    ("__foldl'",                   FoldlStrict,              3),
+    ("__fromJSON",                 FromJSON,                 1),
+    ("fromTOML",                 FromTOML,                 1),
+    ("__functionArgs",             FunctionArgs,             1),
+    ("__genList",                  GenList,                  2),
+    ("__genericClosure",           GenericClosure,           1),
+    ("__getAttr",                  GetAttr,                  2),
+    ("__getContext",               GetContext,               1),
+    ("__getEnv",                   GetEnv,                   1),
+    ("__groupBy",                  GroupBy,                  2),
+    ("__hasAttr",                  HasAttr,                  2),
+    ("__hasContext",               HasContext,               1),
+    ("__hashFile",                 HashFile,                 2),
+    ("__hashString",               HashString,               2),
+    ("__head",                     Head,                     1),
+    ("import",                   Import,                   1),
+    ("__intersectAttrs",           IntersectAttrs,           2),
+    ("__isAttrs",                  IsAttrs,                  1),
+    ("__isBool",                   IsBool,                   1),
+    ("__isFloat",                  IsFloat,                  1),
+    ("__isFunction",               IsFunction,               1),
+    ("__isInt",                    IsInt,                    1),
+    ("__isList",                   IsList,                   1),
+    ("isNull",                   IsNull,                   1),
+    ("__isPath",                   IsPath,                   1),
+    ("__isString",                 IsString,                 1),
+    ("__length",                   Length,                   1),
+    ("__lessThan",                 LessThan,                 2),
+    ("__listToAttrs",              ListToAttrs,              1),
+    ("map",                      Map,                      2),
+    ("__mapAttrs",                 MapAttrs,                 2),
+    ("__match",                    Match,                    2),
+    ("__mul",                      Mul,                      2),
+    ("__parseDrvName",             ParseDrvName,             1),
+    ("__partition",                Partition,                2),
+    ("__path",                     Path,                     1),
+    ("__pathExists",               PathExists,               1),
+    ("placeholder",              Placeholder,              1),
+    ("__readDir",                  ReadDir,                  1),
+    ("__readFile",                 ReadFile,                 1),
+    ("__readFileType",             ReadFileType,             1),
+    ("removeAttrs",              RemoveAttrs,              2),
+    ("__replaceStrings",           ReplaceStrings,           3),
+    ("scopedImport",             ScopedImport,             2),
+    ("__seq",                      Seq,                      2),
+    ("__sort",                     Sort,                     2),
+    ("__split",                    Split,                    2),
+    ("__splitVersion",             SplitVersion,             1),
+    ("__storePath",                StorePath,                1),
+    ("__stringLength",             StringLength,             1),
+    ("__sub",                      Sub,                      2),
+    ("__substring",                Substring,                3),
+    ("__tail",                     Tail,                     1),
+    ("throw",                    Throw,                    1),
+    ("__toFile",                   ToFile,                   2),
+    ("__toJSON",                   ToJSON,                   1),
+    ("__toPath",                   ToPath,                   1),
+    ("toString",                 ToString,                 1),
+    ("__toXML",                    ToXML,                    1),
+    ("__trace",                    Trace,                    2),
+    ("__tryEval",                  TryEval,                  1),
+    ("__typeOf",                   TypeOf,                   1),
+    ("__unsafeDiscardStringContext", UnsafeDiscardStringContext, 1),
+    ("__unsafeDiscardOutputDependency", UnsafeDiscardOutputDependency, 1),
+    ("__unsafeGetAttrPos",         UnsafeGetAttrPos,         2),
+    ("__warn",                     Warn,                     2),
+    ("__zipAttrsWith",             ZipAttrsWith,             2),
+}
+
+#[repr(transparent)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Collect)]
+#[collect(require_static)]
+pub struct StringId(pub string_interner::symbol::SymbolU32);
 
 /// Represents a Nix symbol, which is used as a key in attribute sets.
-#[derive(Debug, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Constructor)]
+#[derive(Debug, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Symbol<'a>(Cow<'a, str>);
 
 pub type StaticSymbol = Symbol<'static>;
@@ -60,13 +185,36 @@ impl Deref for Symbol<'_> {
     }
 }
 
+fn escape_quote_string(s: &str) -> String {
+    let mut ret = String::with_capacity(s.len() + 2);
+    ret.push('"');
+    let mut iter = s.chars().peekable();
+    while let Some(c) = iter.next() {
+        match c {
+            '\\' => ret.push_str("\\\\"),
+            '"' => ret.push_str("\\\""),
+            '\n' => ret.push_str("\\n"),
+            '\r' => ret.push_str("\\r"),
+            '\t' => ret.push_str("\\t"),
+            '$' if iter.peek() == Some(&'{') => ret.push_str("\\$"),
+            c => ret.push(c),
+        }
+    }
+    ret.push('"');
+    ret
+}
+
 /// Represents a Nix attribute set, which is a map from symbols to values.
-#[derive(Constructor, Default, Clone, PartialEq)]
+#[derive(Default, Clone, PartialEq)]
 pub struct AttrSet {
     data: BTreeMap<StaticSymbol, Value>,
 }
 
 impl AttrSet {
+    pub fn new(data: BTreeMap<StaticSymbol, Value>) -> Self {
+        Self { data }
+    }
+
     /// Gets a value by key (string or Symbol).
     pub fn get<'a, 'sym: 'a>(&'a self, key: impl Into<Symbol<'sym>>) -> Option<&'a Value> {
         self.data.get(&key.into())
@@ -154,11 +302,17 @@ impl Display for AttrSetCompatDisplay<'_> {
 }
 
 /// Represents a Nix list, which is a vector of values.
-#[derive(Constructor, Default, Clone, Debug, PartialEq)]
+#[derive(Default, Clone, Debug, PartialEq)]
 pub struct List {
     data: Vec<Value>,
 }
 
+impl List {
+    pub fn new(data: Vec<Value>) -> Self {
+        Self { data }
+    }
+}
+
 impl Deref for List {
     type Target = Vec<Value>;
     fn deref(&self) -> &Self::Target {
@@ -217,7 +371,7 @@ impl Display for ListCompatDisplay<'_> {
 }
 
 /// Represents any possible Nix value that can be returned from an evaluation.
-#[derive(IsVariant, Unwrap, Clone, Debug, PartialEq)]
+#[derive(Clone, Debug, PartialEq)]
 pub enum Value {
     /// An integer value.
     Int(i64),
@@ -240,35 +394,16 @@ pub enum Value {
     /// A function (lambda).
     Func,
     /// A primitive (built-in) operation.
-    PrimOp(String),
+    PrimOp(&'static str),
     /// A partially applied primitive operation.
-    PrimOpApp(String),
+    PrimOpApp(&'static str),
     /// A marker for a value that has been seen before during serialization, to break cycles.
     /// This is used to prevent infinite recursion when printing or serializing cyclic data structures.
     Repeated,
 }
 
-fn escape_quote_string(s: &str) -> String {
-    let mut ret = String::with_capacity(s.len() + 2);
-    ret.push('"');
-    let mut iter = s.chars().peekable();
-    while let Some(c) = iter.next() {
-        match c {
-            '\\' => ret.push_str("\\\\"),
-            '"' => ret.push_str("\\\""),
-            '\n' => ret.push_str("\\n"),
-            '\r' => ret.push_str("\\r"),
-            '\t' => ret.push_str("\\t"),
-            '$' if iter.peek() == Some(&'{') => ret.push_str("\\$"),
-            c => ret.push(c),
-        }
-    }
-    ret.push('"');
-    ret
-}
-
 /// Wrapper to format a float in Nix style (C printf `%g` with precision 6).
-pub(crate) struct NixFloat(pub f64);
+pub struct NixFloat(pub f64);
 
 impl Display for NixFloat {
     fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {

fix-runtime/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "fix-runtime"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+gc-arena = { workspace = true }
+hashbrown = { workspace = true }
+smallvec = { workspace = true }
+sptr = "0.3"
+string-interner = { workspace = true }
+
+fix-bytecode = { path = "../fix-bytecode" }
+fix-error = { path = "../fix-error" }
+fix-lang = { path = "../fix-lang" }

fix-runtime/src/boxing.rs

@@ -1,3 +1,5 @@
+#![allow(dead_code)]
+
 use std::fmt;
 use std::num::NonZeroU8;
 
@@ -22,7 +24,7 @@ impl<T: Default + Copy, const N: usize> ArrayExt<N> for [T; N] {
     }
 }
 
-pub(crate) trait RawStore: Sized {
+pub trait RawStore: Sized {
     fn to_val(self, value: &mut Value);
     fn from_val(value: &Value) -> Self;
 }
@@ -155,9 +157,25 @@ enum TagVal {
 }
 
 #[derive(Copy, Clone, PartialEq, Eq)]
-pub(crate) struct RawTag(TagVal);
+pub struct RawTag(TagVal);
 
 impl RawTag {
+    pub const P1: RawTag = RawTag(TagVal::_P1);
+    pub const P2: RawTag = RawTag(TagVal::_P2);
+    pub const P3: RawTag = RawTag(TagVal::_P3);
+    pub const P4: RawTag = RawTag(TagVal::_P4);
+    pub const P5: RawTag = RawTag(TagVal::_P5);
+    pub const P6: RawTag = RawTag(TagVal::_P6);
+    pub const P7: RawTag = RawTag(TagVal::_P7);
+
+    pub const N1: RawTag = RawTag(TagVal::_N1);
+    pub const N2: RawTag = RawTag(TagVal::_N2);
+    pub const N3: RawTag = RawTag(TagVal::_N3);
+    pub const N4: RawTag = RawTag(TagVal::_N4);
+    pub const N5: RawTag = RawTag(TagVal::_N5);
+    pub const N6: RawTag = RawTag(TagVal::_N6);
+    pub const N7: RawTag = RawTag(TagVal::_N7);
+
     #[inline]
     #[must_use]
     pub(crate) fn new(neg: bool, val: NonZeroU8) -> RawTag {
@@ -193,7 +211,7 @@ impl RawTag {
     /// `val` must be in the range `1..8`
     #[inline]
     #[must_use]
-    pub(crate) unsafe fn new_unchecked(neg: bool, val: u8) -> RawTag {
+    pub(crate) const unsafe fn new_unchecked(neg: bool, val: u8) -> RawTag {
         RawTag(match (neg, val) {
             (false, 1) => TagVal::_P1,
             (false, 2) => TagVal::_P2,
@@ -242,7 +260,7 @@ impl RawTag {
 
     #[inline]
     #[must_use]
-    pub(crate) fn neg_val(self) -> (bool, u8) {
+    pub const fn neg_val(self) -> (bool, u8) {
         match self.0 {
             TagVal::_P1 => (false, 1),
             TagVal::_P2 => (false, 2),
@@ -283,17 +301,17 @@ impl Header {
     }
 
     #[inline]
-    fn tag(self) -> RawTag {
+    const fn tag(self) -> RawTag {
         unsafe { RawTag::new_unchecked(self.get_sign(), self.get_tag()) }
     }
 
     #[inline]
-    fn get_sign(self) -> bool {
+    const fn get_sign(self) -> bool {
         self.0 & 0x8000 != 0
     }
 
     #[inline]
-    fn get_tag(self) -> u8 {
+    const fn get_tag(self) -> u8 {
         (self.0 & 0x0007) as u8
     }
 
@@ -305,7 +323,7 @@ impl Header {
 
 #[derive(Copy, Clone, Debug, PartialEq)]
 #[repr(C, align(8))]
-pub(crate) struct Value {
+pub struct Value {
     #[cfg(target_endian = "big")]
     header: Header,
     data: [u8; 6],
@@ -339,7 +357,7 @@ impl Value {
 
     #[inline]
     #[must_use]
-    pub(crate) fn tag(&self) -> RawTag {
+    pub(crate) const fn tag(&self) -> RawTag {
         self.header.tag()
     }
 
@@ -355,7 +373,7 @@ impl Value {
 
     #[inline]
     #[must_use]
-    pub(crate) fn data(&self) -> &[u8; 6] {
+    pub fn data(&self) -> &[u8; 6] {
         &self.data
     }
 
@@ -415,7 +433,7 @@ impl RawBox {
 
     #[inline]
     #[must_use]
-    pub(crate) fn tag(&self) -> Option<RawTag> {
+    pub(crate) const fn tag(&self) -> Option<RawTag> {
         if self.is_value() {
             Some(unsafe { self.value.tag() })
         } else {
@@ -431,7 +449,7 @@ impl RawBox {
 
     #[inline]
     #[must_use]
-    pub(crate) fn is_value(&self) -> bool {
+    pub(crate) const fn is_value(&self) -> bool {
         (unsafe { self.float.is_nan() } && unsafe { self.bits & SIGN_MASK != QUIET_NAN })
     }
 

fix-runtime/src/forced.rs

@@ -0,0 +1,272 @@
+use fix_lang::StringId;
+use gc_arena::{Gc, Mutation};
+
+use crate::{
+    AttrSet, Break, BytecodeReader, Closure, List, Machine, NixNum, NixString, NixType, Null,
+    PrimOp, PrimOpApp, Step, StrictValue,
+};
+
+pub trait Forced<'gc>: Sized {
+    const WIDTH: usize;
+
+    /// Force and type-check the `WIDTH` slots starting at `base_depth` from
+    /// TOS, deepest-first. If a slot holds a thunk, enter it and return
+    /// `Break::Force`. If a slot holds a value of the wrong type, call
+    /// `finish_type_err` and return `Break::Done`.
+    fn force_and_check<M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        base_depth: usize,
+        resume_pc: usize,
+    ) -> Step;
+
+    /// After `force_and_check` returned `Continue`, pop `WIDTH` slots
+    /// (TOS first) and convert. Type assertions are infallible because
+    /// `force_and_check` already validated every slot.
+    fn pop_converted<M: Machine<'gc>>(m: &mut M) -> Self;
+}
+
+impl<'gc> Forced<'gc> for StrictValue<'gc> {
+    const WIDTH: usize = 1;
+
+    #[inline(always)]
+    fn force_and_check<M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        base_depth: usize,
+        resume_pc: usize,
+    ) -> Step {
+        m.force_slot_to_pc(base_depth, reader, mc, resume_pc)
+    }
+
+    #[inline(always)]
+    fn pop_converted<M: Machine<'gc>>(m: &mut M) -> Self {
+        m.pop_forced()
+    }
+}
+
+macro_rules! impl_forced_inline {
+    ($($ty:ty => $nix_ty:expr),* $(,)?) => {
+        $(
+        impl<'gc> Forced<'gc> for $ty {
+            const WIDTH: usize = 1;
+
+            #[inline(always)]
+            fn force_and_check<M: Machine<'gc>>(
+                m: &mut M,
+                reader: &mut BytecodeReader<'_>,
+                mc: &Mutation<'gc>,
+                base_depth: usize,
+                resume_pc: usize,
+            ) -> Step {
+                m.force_slot_to_pc(base_depth, reader, mc, resume_pc)?;
+                let v = m.peek_forced(base_depth);
+                if v.as_inline::<$ty>().is_none() {
+                    let _: Step = m.finish_type_err($nix_ty, v.ty());
+                    return Step::Break(Break::Done);
+                }
+                Step::Continue(())
+            }
+
+            #[inline(always)]
+            fn pop_converted<M: Machine<'gc>>(m: &mut M) -> Self {
+                m.pop_forced()
+                    .as_inline::<$ty>()
+                    .expect("type checked in force_and_check")
+            }
+        }
+        )*
+    };
+}
+
+macro_rules! impl_forced_gc {
+    ($($ty:ty => $nix_ty:expr),* $(,)?) => {
+        $(
+        impl<'gc> Forced<'gc> for Gc<'gc, $ty> {
+            const WIDTH: usize = 1;
+
+            #[inline(always)]
+            fn force_and_check<M: Machine<'gc>>(
+                m: &mut M,
+                reader: &mut BytecodeReader<'_>,
+                mc: &Mutation<'gc>,
+                base_depth: usize,
+                resume_pc: usize,
+            ) -> Step {
+                m.force_slot_to_pc(base_depth, reader, mc, resume_pc)?;
+                let v = m.peek_forced(base_depth);
+                if v.as_gc::<$ty>().is_none() {
+                    let _: Step = m.finish_type_err($nix_ty, v.ty());
+                    return Step::Break(Break::Done);
+                }
+                Step::Continue(())
+            }
+
+            #[inline(always)]
+            fn pop_converted<M: Machine<'gc>>(m: &mut M) -> Self {
+                m.pop_forced()
+                    .as_gc::<$ty>()
+                    .expect("type checked in force_and_check")
+            }
+        }
+        )*
+    };
+}
+
+impl_forced_inline! {
+    i32 => NixType::Int,
+    bool => NixType::Bool,
+    Null => NixType::Null,
+    StringId => NixType::String,
+    PrimOp => NixType::PrimOp,
+}
+
+impl_forced_gc! {
+    i64 => NixType::Int,
+    NixString => NixType::String,
+    AttrSet<'gc> => NixType::AttrSet,
+    List<'gc> => NixType::List,
+    Closure<'gc> => NixType::Closure,
+    PrimOpApp<'gc> => NixType::PrimOpApp,
+}
+
+impl<'gc> Forced<'gc> for NixNum {
+    const WIDTH: usize = 1;
+
+    #[inline(always)]
+    fn force_and_check<M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        base_depth: usize,
+        resume_pc: usize,
+    ) -> Step {
+        m.force_slot_to_pc(base_depth, reader, mc, resume_pc)?;
+        let v = m.peek_forced(base_depth);
+        if v.as_num().is_none() {
+            let _: Step = m.finish_type_err(NixType::Int, v.ty());
+            return Step::Break(Break::Done);
+        }
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    fn pop_converted<M: Machine<'gc>>(m: &mut M) -> Self {
+        m.pop_forced()
+            .as_num()
+            .expect("type checked in force_and_check")
+    }
+}
+
+impl<'gc> Forced<'gc> for f64 {
+    const WIDTH: usize = 1;
+
+    #[inline(always)]
+    fn force_and_check<M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        base_depth: usize,
+        resume_pc: usize,
+    ) -> Step {
+        m.force_slot_to_pc(base_depth, reader, mc, resume_pc)?;
+        let v = m.peek_forced(base_depth);
+        if v.as_float().is_none() {
+            let _: Step = m.finish_type_err(NixType::Float, v.ty());
+            return Step::Break(Break::Done);
+        }
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    fn pop_converted<M: Machine<'gc>>(m: &mut M) -> Self {
+        m.pop_forced()
+            .as_float()
+            .expect("type checked in force_and_check")
+    }
+}
+
+impl<'gc, A: Forced<'gc>, B: Forced<'gc>> Forced<'gc> for (A, B) {
+    const WIDTH: usize = A::WIDTH + B::WIDTH;
+
+    #[inline(always)]
+    fn force_and_check<M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        base: usize,
+        resume_pc: usize,
+    ) -> Step {
+        A::force_and_check(m, reader, mc, base + B::WIDTH, resume_pc)?;
+        B::force_and_check(m, reader, mc, base, resume_pc)
+    }
+
+    #[inline(always)]
+    fn pop_converted<M: Machine<'gc>>(m: &mut M) -> Self {
+        let b = B::pop_converted(m);
+        let a = A::pop_converted(m);
+        (a, b)
+    }
+}
+
+impl<'gc, A: Forced<'gc>, B: Forced<'gc>, C: Forced<'gc>> Forced<'gc> for (A, B, C) {
+    const WIDTH: usize = A::WIDTH + B::WIDTH + C::WIDTH;
+
+    #[inline(always)]
+    fn force_and_check<M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        base: usize,
+        resume_pc: usize,
+    ) -> Step {
+        A::force_and_check(m, reader, mc, base + B::WIDTH + C::WIDTH, resume_pc)?;
+        B::force_and_check(m, reader, mc, base + C::WIDTH, resume_pc)?;
+        C::force_and_check(m, reader, mc, base, resume_pc)
+    }
+
+    #[inline(always)]
+    fn pop_converted<M: Machine<'gc>>(m: &mut M) -> Self {
+        let c = C::pop_converted(m);
+        let b = B::pop_converted(m);
+        let a = A::pop_converted(m);
+        (a, b, c)
+    }
+}
+
+impl<'gc, A: Forced<'gc>, B: Forced<'gc>, C: Forced<'gc>, D: Forced<'gc>> Forced<'gc>
+    for (A, B, C, D)
+{
+    const WIDTH: usize = A::WIDTH + B::WIDTH + C::WIDTH + D::WIDTH;
+
+    #[inline(always)]
+    fn force_and_check<M: Machine<'gc>>(
+        m: &mut M,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        base: usize,
+        resume_pc: usize,
+    ) -> Step {
+        A::force_and_check(
+            m,
+            reader,
+            mc,
+            base + B::WIDTH + C::WIDTH + D::WIDTH,
+            resume_pc,
+        )?;
+        B::force_and_check(m, reader, mc, base + C::WIDTH + D::WIDTH, resume_pc)?;
+        C::force_and_check(m, reader, mc, base + D::WIDTH, resume_pc)?;
+        D::force_and_check(m, reader, mc, base, resume_pc)
+    }
+
+    #[inline(always)]
+    fn pop_converted<M: Machine<'gc>>(m: &mut M) -> Self {
+        let d = D::pop_converted(m);
+        let c = C::pop_converted(m);
+        let b = B::pop_converted(m);
+        let a = A::pop_converted(m);
+        (a, b, c, d)
+    }
+}

fix-runtime/src/host.rs

@@ -0,0 +1,165 @@
+use fix_bytecode::InstructionPtr;
+use fix_error::Source;
+use fix_lang::{self, BUILTINS, StringId};
+use hashbrown::HashSet;
+
+use crate::{
+    AttrSet, Closure, ExtraScope, List, NixString, NixType, Null, Path, PrimOp, PrimOpApp,
+    StaticValue, StrictValue, StringContext, Thunk, ThunkState, Value,
+};
+
+pub trait VmContext {
+    fn split(&mut self) -> (&mut impl VmCode, &mut impl VmRuntimeCtx);
+}
+
+pub trait VmRuntimeCtx {
+    fn intern_string(&mut self, s: impl AsRef<str>) -> StringId;
+    fn resolve_string(&self, id: StringId) -> &str;
+    fn get_const(&self, id: u32) -> StaticValue;
+    fn add_const(&mut self, val: StaticValue) -> u32;
+}
+
+pub trait VmCode {
+    fn bytecode(&self) -> &[u8];
+    fn compile_with_scope(
+        &mut self,
+        source: Source,
+        extra_scope: Option<ExtraScope>,
+        ctx: &mut impl VmRuntimeCtx,
+    ) -> fix_error::Result<InstructionPtr>;
+}
+
+pub trait VmRuntimeCtxExt: VmRuntimeCtx {
+    fn get_string<'a, 'gc: 'a>(&'a self, val: StrictValue<'gc>) -> Option<&'a str>;
+    fn get_string_or_path<'a, 'gc: 'a>(&'a self, val: StrictValue<'gc>) -> Option<&'a str>;
+    fn get_string_id<'a, 'gc: 'a>(
+        &'a mut self,
+        val: StrictValue<'gc>,
+    ) -> std::result::Result<StringId, NixType>;
+    /// Returns the string context attached to `val`, or `&[]` if `val` is
+    /// either a non-string or a string without context.
+    fn get_string_context<'gc>(&self, val: StrictValue<'gc>) -> &'gc StringContext;
+    fn convert_value(&self, val: Value) -> fix_lang::Value;
+}
+
+impl<T: VmRuntimeCtx> VmRuntimeCtxExt for T {
+    fn get_string<'a, 'gc: 'a>(&'a self, val: StrictValue<'gc>) -> Option<&'a str> {
+        if let Some(sid) = val.as_inline::<StringId>() {
+            Some(self.resolve_string(sid))
+        } else {
+            val.as_gc::<NixString>().map(|ns| ns.as_ref().as_str())
+        }
+    }
+
+    /// Like `get_string`, but also accepts `Path` values (returning their
+    /// underlying canonical-path string). Use this in places where Nix
+    /// would coerce a path to a string (string interpolation, file IO
+    /// builtins, etc.).
+    fn get_string_or_path<'a, 'gc: 'a>(&'a self, val: StrictValue<'gc>) -> Option<&'a str> {
+        if let Some(p) = val.as_inline::<Path>() {
+            Some(self.resolve_string(p.0))
+        } else {
+            self.get_string(val)
+        }
+    }
+
+    fn get_string_id<'a, 'gc: 'a>(
+        &'a mut self,
+        val: StrictValue<'gc>,
+    ) -> std::result::Result<StringId, NixType> {
+        if let Some(sid) = val.as_inline::<StringId>() {
+            Ok(sid)
+        } else if let Some(s) = val.as_gc::<NixString>().map(|ns| ns.as_ref().as_str()) {
+            Ok(self.intern_string(s))
+        } else {
+            Err(val.ty())
+        }
+    }
+
+    fn get_string_context<'gc>(&self, val: StrictValue<'gc>) -> &'gc StringContext {
+        if let Some(ns) = val.as_gc::<NixString>() {
+            ns.as_ref().context()
+        } else {
+            StringContext::empty()
+        }
+    }
+
+    fn convert_value(&self, val: Value) -> fix_lang::Value {
+        self.convert_value_with_seen(val, &mut HashSet::new())
+    }
+}
+
+pub(crate) trait ConvertValueWithSeen: VmRuntimeCtx {
+    fn convert_value_with_seen(&self, val: Value, seen: &mut HashSet<u64>) -> fix_lang::Value;
+}
+
+impl<T: VmRuntimeCtx> ConvertValueWithSeen for T {
+    fn convert_value_with_seen(&self, val: Value, seen: &mut HashSet<u64>) -> fix_lang::Value {
+        use fix_lang::Value;
+        if let Some(i) = val.as_inline::<i32>() {
+            Value::Int(i as i64)
+        } else if let Some(gc_i) = val.as_gc::<i64>() {
+            Value::Int(*gc_i)
+        } else if let Some(f) = val.as_float() {
+            Value::Float(f)
+        } else if let Some(b) = val.as_inline::<bool>() {
+            Value::Bool(b)
+        } else if val.is::<Null>() {
+            Value::Null
+        } else if let Some(sid) = val.as_inline::<StringId>() {
+            let s = self.resolve_string(sid).to_owned();
+            Value::String(s)
+        } else if let Some(ns) = val.as_gc::<NixString>() {
+            Value::String(ns.as_str().to_owned())
+        } else if let Some(p) = val.as_inline::<Path>() {
+            Value::Path(self.resolve_string(p.0).to_owned())
+        } else if let Some(attrs) = val.as_gc::<AttrSet>() {
+            let bits = val.to_bits();
+            if attrs.entries.is_empty() {
+                return Value::AttrSet(Default::default());
+            }
+            if !seen.insert(bits) {
+                return Value::Repeated;
+            }
+            let mut map = std::collections::BTreeMap::new();
+            for &(key, val) in attrs.entries.iter() {
+                let key = self.resolve_string(key).to_owned();
+                let converted = self.convert_value_with_seen(val, seen);
+                map.insert(fix_lang::Symbol::from(key), converted);
+            }
+            Value::AttrSet(fix_lang::AttrSet::new(map))
+        } else if let Some(list) = val.as_gc::<List>() {
+            let bits = val.to_bits();
+            if list.inner.borrow().is_empty() {
+                return Value::List(Default::default());
+            }
+            if !seen.insert(bits) {
+                return Value::Repeated;
+            }
+            let items: Vec<_> = list
+                .inner
+                .borrow()
+                .iter()
+                .copied()
+                .map(|v| self.convert_value_with_seen(v, seen))
+                .collect();
+            Value::List(fix_lang::List::new(items))
+        } else if val.is::<Closure>() {
+            Value::Func
+        } else if let Some(thunk) = val.as_gc::<Thunk>() {
+            if let ThunkState::Evaluated(v) = *thunk.borrow() {
+                self.convert_value_with_seen(v.relax(), seen)
+            } else {
+                Value::Thunk
+            }
+        } else if let Some(primop) = val.as_inline::<PrimOp>() {
+            let name = BUILTINS[primop.id as usize].0;
+            Value::PrimOp(name.strip_prefix("__").unwrap_or(name))
+        } else if let Some(app) = val.as_gc::<PrimOpApp>() {
+            let name = BUILTINS[app.primop.id as usize].0;
+            Value::PrimOpApp(name.strip_prefix("__").unwrap_or(name))
+        } else {
+            Value::Null
+        }
+    }
+}

fix-runtime/src/lib.rs

@@ -0,0 +1,19 @@
+mod boxing;
+mod forced;
+mod host;
+mod machine;
+mod path_util;
+mod resolve;
+mod state;
+mod string_context;
+mod value;
+
+pub use fix_bytecode::{BytecodeReader, OperandData};
+pub use forced::*;
+pub use host::*;
+pub use machine::*;
+pub use path_util::*;
+pub use resolve::*;
+pub use state::*;
+pub use string_context::*;
+pub use value::*;

fix-runtime/src/machine.rs

@@ -0,0 +1,178 @@
+use std::ops::ControlFlow;
+use std::path::{Path, PathBuf};
+
+use fix_error::Error;
+use fix_lang::{self, StringId};
+use gc_arena::Mutation;
+
+use crate::{
+    Break, BytecodeReader, CallFrame, ForceMode, Forced, GcEnv, NixType, PendingLoad, Step,
+    StrictValue, Value, VmError,
+};
+
+/// Abstract VM-side operations consumed by instruction handlers and primops.
+///
+/// Implementors maintain a value stack, a call stack, an environment chain,
+/// pending result/error state, and a set of GC-allocated globals. Methods
+/// fall into a few groups:
+///
+/// - Stack ops (`push` / `pop` / `peek` / `replace` / `pop_forced` / ...)
+/// - Forcing primitives (`force_slot` / `force_slot_to_pc`)
+/// - Calling (`call` / `return_from_primop`)
+/// - Call-frame management (`push_call_frame` / `pop_call_frame` / call-depth)
+/// - Environment access (`env` / `set_env` / `local`)
+/// - Result finalization (`finish_ok` / `finish_err` / ...)
+/// - Global lookup (`builtins` / `empty_list` / `empty_attrs` / ...)
+/// - Imports and scope slots (`import_cache_*` / `scope_slot*` / `set_pending_load`)
+pub trait Machine<'gc> {
+    fn push(&mut self, val: Value<'gc>);
+    #[must_use]
+    fn pop(&mut self) -> Value<'gc>;
+    #[must_use]
+    fn peek(&self, depth: usize) -> Value<'gc>;
+    #[must_use]
+    fn peek_forced(&self, depth: usize) -> StrictValue<'gc>;
+    fn pop_forced(&mut self) -> StrictValue<'gc>;
+    fn replace(&mut self, depth: usize, val: Value<'gc>);
+    fn drop_n(&mut self, depth: usize);
+    fn stack_len(&self) -> usize;
+
+    fn force_slot_to_pc(
+        &mut self,
+        depth: usize,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        resume_pc: usize,
+    ) -> Step;
+
+    #[inline(always)]
+    fn force_slot(
+        &mut self,
+        depth: usize,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let pc = reader.inst_start_pc();
+        self.force_slot_to_pc(depth, reader, mc, pc)
+    }
+
+    fn call(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        arg: Value<'gc>,
+        resume_pc: usize,
+    ) -> Step;
+
+    #[inline(always)]
+    fn return_from_primop(&mut self, val: Value<'gc>, reader: &mut BytecodeReader<'_>) -> Step {
+        self.push(val);
+        let Some(CallFrame {
+            pc: ret_pc,
+            thunk: _,
+            env,
+        }) = self.pop_call_frame()
+        else {
+            unreachable!()
+        };
+        reader.set_pc(ret_pc);
+        self.dec_call_depth();
+        self.set_env(env);
+        Step::Continue(())
+    }
+
+    fn push_call_frame(&mut self, frame: CallFrame<'gc>);
+    fn pop_call_frame(&mut self) -> Option<CallFrame<'gc>>;
+    fn call_depth(&self) -> usize;
+    fn inc_call_depth(&mut self);
+    fn dec_call_depth(&mut self);
+
+    fn env(&self) -> GcEnv<'gc>;
+    fn set_env(&mut self, env: GcEnv<'gc>);
+
+    #[inline(always)]
+    fn local(&self, layer: u8, idx: u32) -> Value<'gc> {
+        let mut cur = self.env();
+        for _ in 0..layer {
+            let prev = cur.borrow().prev.expect("env chain too short");
+            cur = prev;
+        }
+        cur.borrow().locals[idx as usize]
+    }
+
+    fn finish_ok(&mut self, val: fix_lang::Value) -> Step;
+    fn finish_err(&mut self, err: Box<Error>) -> Step;
+    fn finish_type_err(&mut self, expected: NixType, got: NixType) -> Step;
+
+    #[inline(always)]
+    fn finish_vm_err(&mut self, err: VmError) -> Step {
+        self.finish_err(err.into_error())
+    }
+
+    fn builtins(&self) -> Value<'gc>;
+    fn functor_sym(&self) -> StringId;
+    fn empty_list(&self) -> Value<'gc>;
+    fn empty_attrs(&self) -> Value<'gc>;
+    fn force_mode(&self) -> ForceMode;
+
+    fn import_cache_get(&self, path: &Path) -> Option<Value<'gc>>;
+    fn import_cache_insert(&mut self, path: PathBuf, val: Value<'gc>);
+    fn scope_slot(&self, idx: u32) -> Value<'gc>;
+    fn scope_slots_push(&mut self, val: Value<'gc>) -> u32;
+    fn set_pending_load(&mut self, load: PendingLoad);
+}
+
+/// Extension trait with convenience helpers built on top of [`Machine`].
+///
+/// Auto-implemented for every `Machine<'gc>` so callers just need to bring
+/// `MachineExt` (or `Machine`) into scope.
+pub trait MachineExt<'gc>: Machine<'gc> {
+    /// Force the top `T::WIDTH` stack slots and return them as `T`.
+    ///
+    /// If any slot holds a pending thunk, this method pushes a call frame
+    /// whose resume PC is the **start of the current instruction**
+    /// (`reader.inst_start_pc()`), enters the thunk, and returns
+    /// `Break::Force`. When the thunk eventually returns, the VM will
+    /// **re-execute the entire opcode handler from the beginning**.
+    ///
+    /// # Invariants
+    ///
+    /// * **Do not call this method more than once in a single handler.**
+    ///   If you need to force multiple values, use a tuple type such as
+    ///   `(StrictValue, StrictValue)` so they are forced and popped in one
+    ///   atomic operation.
+    /// * The stack layout at the call site must be **identical** every time
+    ///   the handler is re-entered.
+    /// * Propagate the return value with `?` so `Break::Force` correctly
+    ///   unwinds to the dispatch loop.
+    #[inline(always)]
+    fn force_and_retry<T: Forced<'gc>>(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> ControlFlow<Break, T>
+    where
+        Self: Sized,
+    {
+        let pc = reader.inst_start_pc();
+        self.force_and_retry_pc(reader, mc, pc)
+    }
+
+    /// Same as [`force_and_retry`](Self::force_and_retry) but allows
+    /// specifying a custom resume PC.
+    #[inline(always)]
+    fn force_and_retry_pc<T: Forced<'gc>>(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        resume_pc: usize,
+    ) -> ControlFlow<Break, T>
+    where
+        Self: Sized,
+    {
+        T::force_and_check(self, reader, mc, 0, resume_pc)?;
+        ControlFlow::Continue(T::pop_converted(self))
+    }
+}
+
+impl<'gc, M: Machine<'gc>> MachineExt<'gc> for M {}

fix-runtime/src/path_util.rs

@@ -0,0 +1,18 @@
+use std::path::{Component, PathBuf};
+
+pub fn canon_path_str(path: impl AsRef<std::path::Path>) -> String {
+    let p = path.as_ref();
+    let mut normalized = PathBuf::new();
+    for component in p.components() {
+        match component {
+            Component::Prefix(p) => normalized.push(p.as_os_str()),
+            Component::RootDir => normalized.push("/"),
+            Component::CurDir => {}
+            Component::ParentDir => {
+                normalized.pop();
+            }
+            Component::Normal(c) => normalized.push(c),
+        }
+    }
+    normalized.to_string_lossy().into_owned()
+}

fix-runtime/src/resolve.rs

@@ -0,0 +1,35 @@
+use fix_bytecode::OperandData;
+use gc_arena::{Gc, Mutation};
+
+use crate::{AttrSet, Machine, Value, VmRuntimeCtx};
+
+/// Resolve a decoded operand into a runtime [`Value`].
+///
+/// The operand decoder ([`crate::BytecodeReader::read_operand_data`])
+/// produces a static enum; this function materializes it against the
+/// running [`Machine`] (env chain, builtins, scope slots, ...).
+#[inline]
+pub fn resolve_operand<'gc, M: Machine<'gc>>(
+    op: &OperandData,
+    mc: &Mutation<'gc>,
+    ctx: &impl VmRuntimeCtx,
+    m: &M,
+) -> Value<'gc> {
+    use OperandData::*;
+    match *op {
+        Const(id) => ctx.get_const(id).into(),
+        BigInt(val) => Value::new_gc(Gc::new(mc, val)),
+        Local { layer, idx } => m.local(layer, idx),
+        #[allow(clippy::unwrap_used)]
+        BuiltinConst(id) => m.builtins().as_gc::<AttrSet>().unwrap().lookup(id).unwrap(),
+        Builtins => m.builtins(),
+        ReplBinding(_id) => todo!(),
+        ScopedImportBinding { slot_id, name } => {
+            let scope = m.scope_slot(slot_id);
+            #[allow(clippy::unwrap_used)]
+            let attrs = scope.as_gc::<AttrSet>().expect("scope must be attrset");
+            #[allow(clippy::unwrap_used)]
+            attrs.lookup(name).expect("scoped binding not found")
+        }
+    }
+}

fix-runtime/src/state.rs

@@ -0,0 +1,89 @@
+use std::ops::ControlFlow;
+use std::path::PathBuf;
+
+use fix_error::Error;
+use fix_lang::StringId;
+use gc_arena::{Collect, Gc};
+use hashbrown::HashSet;
+
+use crate::{GcEnv, Thunk};
+
+#[allow(dead_code)]
+pub enum VmError {
+    Catchable(String),
+    Uncatchable(Box<Error>),
+}
+
+impl From<Box<Error>> for VmError {
+    fn from(e: Box<Error>) -> Self {
+        VmError::Uncatchable(e)
+    }
+}
+
+impl VmError {
+    pub fn into_error(self) -> Box<Error> {
+        match self {
+            VmError::Catchable(_) => todo!("Check for tryEval catch frames"),
+            VmError::Uncatchable(e) => e,
+        }
+    }
+}
+
+pub fn vm_err(msg: impl Into<String>) -> VmError {
+    VmError::Uncatchable(Error::eval_error(msg.into()))
+}
+
+#[derive(Collect, Clone, Copy, Debug, PartialEq, Eq, Default)]
+#[collect(require_static)]
+pub enum ForceMode {
+    #[default]
+    AsIs,
+    Shallow,
+    Deep,
+}
+
+#[repr(u8)]
+pub enum Break {
+    Force,
+    Done,
+    LoadFile,
+}
+
+pub type Step = ControlFlow<Break>;
+
+#[allow(dead_code)]
+pub struct ErrorFrame {
+    pub span_id: u32,
+    pub message: Option<String>,
+}
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub struct CallFrame<'gc> {
+    pub pc: usize,
+    pub thunk: Option<Gc<'gc, Thunk<'gc>>>,
+    pub env: GcEnv<'gc>,
+}
+
+#[derive(Debug)]
+pub struct PendingLoad {
+    pub path: PathBuf,
+    pub scope: Option<PendingScope>,
+}
+
+#[derive(Debug)]
+pub struct PendingScope {
+    pub keys: HashSet<StringId>,
+    pub slot_id: u32,
+}
+
+/// Extra scope passed to a re-entrant compile from inside a running VM.
+///
+/// Currently only `ScopedImport` is produced (by the `scopedImport` builtin),
+/// but the variant is kept open so REPL bindings could later land here too.
+pub enum ExtraScope {
+    ScopedImport {
+        keys: HashSet<StringId>,
+        slot_id: u32,
+    },
+}

fix-runtime/src/string_context.rs

@@ -0,0 +1,161 @@
+use std::cmp::Ordering;
+
+use smallvec::SmallVec;
+
+/// A string context element
+#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum StringContextElem {
+    // Plain store path reference
+    Opaque {
+        path: Box<str>,
+    },
+    // All outputs of a derivation
+    // encoded `=<drvPath>`
+    DrvDeep {
+        drv_path: Box<str>,
+    },
+    // A specific output of a derivation
+    // encoded `!<output>!<drvPath>`
+    Built {
+        drv_path: Box<str>,
+        output: Box<str>,
+    },
+}
+
+impl StringContextElem {
+    /// Decode the CppNix wire form (`!out!/p`, `=/p`, `/p`). Falls back to
+    /// `Opaque` for malformed `!`-prefixed inputs (matching nix-js).
+    pub fn decode(encoded: &str) -> Self {
+        if let Some(drv_path) = encoded.strip_prefix('=') {
+            Self::DrvDeep {
+                drv_path: drv_path.into(),
+            }
+        } else if let Some(rest) = encoded.strip_prefix('!') {
+            if let Some(second_bang) = rest.find('!') {
+                Self::Built {
+                    output: rest[..second_bang].into(),
+                    drv_path: rest[second_bang + 1..].into(),
+                }
+            } else {
+                Self::Opaque {
+                    path: encoded.into(),
+                }
+            }
+        } else {
+            Self::Opaque {
+                path: encoded.into(),
+            }
+        }
+    }
+
+    pub fn encode(&self) -> String {
+        match self {
+            Self::Opaque { path } => path.to_string(),
+            Self::DrvDeep { drv_path } => format!("={drv_path}"),
+            Self::Built { drv_path, output } => format!("!{output}!{drv_path}"),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct StringContext {
+    data: SmallVec<[StringContextElem; 1]>,
+}
+
+impl IntoIterator for StringContext {
+    type Item = StringContextElem;
+    type IntoIter = <SmallVec<[StringContextElem; 1]> as IntoIterator>::IntoIter;
+    fn into_iter(self) -> Self::IntoIter {
+        self.data.into_iter()
+    }
+}
+
+impl<'a> IntoIterator for &'a StringContext {
+    type Item = &'a StringContextElem;
+    type IntoIter = <&'a SmallVec<[StringContextElem; 1]> as IntoIterator>::IntoIter;
+    fn into_iter(self) -> Self::IntoIter {
+        self.data.iter()
+    }
+}
+
+impl<'a> IntoIterator for &'a mut StringContext {
+    type Item = &'a mut StringContextElem;
+    type IntoIter = <&'a mut SmallVec<[StringContextElem; 1]> as IntoIterator>::IntoIter;
+    fn into_iter(self) -> Self::IntoIter {
+        self.data.iter_mut()
+    }
+}
+
+impl FromIterator<StringContextElem> for StringContext {
+    fn from_iter<T: IntoIterator<Item = StringContextElem>>(iter: T) -> Self {
+        Self {
+            data: iter.into_iter().collect(),
+        }
+    }
+}
+
+impl StringContext {
+    pub fn empty() -> &'static Self {
+        static EMPTY: StringContext = StringContext {
+            data: SmallVec::new_const(),
+        };
+        &EMPTY
+    }
+
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.data.is_empty()
+    }
+
+    pub fn insert(&mut self, elem: StringContextElem) {
+        match self.data.binary_search(&elem) {
+            Ok(_) => {}
+            Err(pos) => self.data.insert(pos, elem),
+        }
+    }
+
+    pub fn merge(&self, other: &Self) -> Self {
+        if self.data.is_empty() {
+            return other.clone();
+        }
+        if other.data.is_empty() {
+            return self.clone();
+        }
+
+        let a = &self.data;
+        let b = &other.data;
+        let mut out = SmallVec::with_capacity(a.len() + b.len());
+        let (mut i, mut j) = (0, 0);
+        while i < a.len() && j < b.len() {
+            match a[i].cmp(&b[j]) {
+                Ordering::Less => {
+                    out.push(a[i].clone());
+                    i += 1;
+                }
+                Ordering::Greater => {
+                    out.push(b[j].clone());
+                    j += 1;
+                }
+                Ordering::Equal => {
+                    out.push(a[i].clone());
+                    i += 1;
+                    j += 1;
+                }
+            }
+        }
+        out.extend(a[i..].iter().cloned());
+        out.extend(b[j..].iter().cloned());
+        Self { data: out }
+    }
+
+    pub fn iter(&self) -> <&Self as IntoIterator>::IntoIter {
+        self.into_iter()
+    }
+
+    pub fn iter_mut(&mut self) -> <&mut Self as IntoIterator>::IntoIter {
+        self.into_iter()
+    }
+}

fix-runtime/src/value.rs

@@ -0,0 +1,730 @@
+use std::cell::RefCell;
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem::size_of;
+use std::ops::Deref;
+
+use fix_lang::*;
+use gc_arena::barrier::Unlock;
+use gc_arena::collect::Trace;
+use gc_arena::{Collect, Gc, GcRefLock, Mutation, RefLock};
+use smallvec::SmallVec;
+use string_interner::Symbol;
+use string_interner::symbol::SymbolU32;
+
+use crate::boxing::{RawBox, RawStore, RawTag, Value as RawValue};
+use crate::string_context::StringContext;
+
+mod private {
+    pub trait Cealed {}
+}
+
+/// # Safety
+///
+/// [`Self::TAG`] must be unique among all implementors.
+unsafe trait Storable: private::Cealed {
+    const TAG: RawTag;
+}
+trait InlineStorable: Storable + RawStore {}
+trait GcStorable: Storable {}
+
+macro_rules! define_value_types {
+    (
+        inline { $($itype:ty => $itag:expr, $iname:literal;)* }
+        gc { $($gtype:ty => $gtag:expr, $gname:literal;)* }
+    ) => {
+        $(
+        unsafe impl Storable for $itype {
+            const TAG: RawTag = $itag;
+        }
+        impl InlineStorable for $itype {}
+        impl private::Cealed for $itype {}
+        )*
+        $(
+        unsafe impl Storable for $gtype {
+            const TAG: RawTag = $gtag;
+        }
+        impl GcStorable for $gtype {}
+        impl private::Cealed for $gtype {}
+        )*
+
+        const _: () = assert!(size_of::<Value<'static>>() == 8);
+        $(const _: () = assert!(size_of::<$itype>() <= 6);)*
+
+        const _: () = {
+            let tags: &[(bool, u8)] = &[$(RawTag::neg_val($itag)),*, $(RawTag::neg_val($gtag)),*];
+            let mut mask_false: u8 = 0;
+            let mut mask_true: u8 = 0;
+            let mut i = 0;
+            while i < tags.len() {
+                let (neg, val) = tags[i];
+                let bit = 1 << val;
+                if neg {
+                    assert!(mask_true & bit == 0, "duplicate true tag id");
+                    mask_true |= bit;
+                } else {
+                    assert!(mask_false & bit == 0, "duplicate false tag id");
+                    mask_false |= bit;
+                }
+                i += 1;
+            }
+        };
+
+        unsafe impl<'gc> Collect<'gc> for Value<'gc> {
+            const NEEDS_TRACE: bool = true;
+            fn trace<T: Trace<'gc>>(&self, cc: &mut T) {
+                let Some(tag) = self.raw.tag() else { return };
+                match tag {
+                    $(<$gtype as Storable>::TAG => unsafe {
+                        self.load_gc::<$gtype>().trace(cc)
+                    },)*
+                    $(<$itype as Storable>::TAG => (),)*
+                    _ => unreachable!("invalid value tag"),
+                }
+            }
+        }
+
+        impl fmt::Debug for Value<'_> {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                match self.tag() {
+                    None => write!(f, "Float({:?})", unsafe {
+                        self.raw.float().unwrap_unchecked()
+                    }),
+                    $(Some(<$itype as Storable>::TAG) => write!(f, "{}({:?})", $iname, unsafe {
+                        self.as_inline::<$itype>().unwrap_unchecked()
+                    }),)*
+                    $(Some(<$gtype as Storable>::TAG) =>
+                        write!(f, "{}(..)", $gname),)*
+                    _ => unreachable!("invalid value tag"),
+                }
+            }
+        }
+    };
+}
+
+define_value_types! {
+    inline {
+        i32 => RawTag::P1, "SmallInt";
+        bool => RawTag::P2, "Bool";
+        Null => RawTag::P3, "Null";
+        StringId => RawTag::P4, "SmallString";
+        PrimOp => RawTag::P5, "PrimOp";
+        Path => RawTag::P6, "Path";
+    }
+    gc {
+        i64 => RawTag::P7, "BigInt";
+        NixString => RawTag::N1, "String";
+        AttrSet<'_> => RawTag::N2, "AttrSet";
+        List<'_> => RawTag::N3, "List";
+        Thunk<'_> => RawTag::N4, "Thunk";
+        Closure<'_> => RawTag::N5, "Closure";
+        PrimOpApp<'_> => RawTag::N6, "PrimOpApp";
+    }
+}
+
+/// # Nix runtime value representation
+///
+/// NaN-boxed value fitting in 8 bytes.
+#[derive(Copy, Clone)]
+#[repr(transparent)]
+pub struct Value<'gc> {
+    raw: RawBox,
+    _marker: PhantomData<Gc<'gc, ()>>,
+}
+
+impl Default for Value<'_> {
+    #[inline(always)]
+    fn default() -> Self {
+        Self::new_inline(Null)
+    }
+}
+
+impl<'gc> Value<'gc> {
+    #[inline(always)]
+    fn from_raw_value(rv: RawValue) -> Self {
+        Self {
+            raw: RawBox::from_value(rv),
+            _marker: PhantomData,
+        }
+    }
+
+    /// Load a GC pointer from a value with a negative tag.
+    ///
+    /// # Safety
+    ///
+    /// The value must actually store a `Gc<'gc, T>` with the matching type.
+    #[inline(always)]
+    unsafe fn load_gc<T: GcStorable>(self) -> Gc<'gc, T> {
+        unsafe {
+            let rv = self.raw.value().unwrap_unchecked();
+            let ptr: *const T = <*const T as RawStore>::from_val(rv);
+            Gc::from_ptr(ptr)
+        }
+    }
+
+    #[inline(always)]
+    const fn tag(self) -> Option<RawTag> {
+        self.raw.tag()
+    }
+}
+
+impl<'gc> Value<'gc> {
+    #[inline]
+    pub fn new_float(val: f64) -> Self {
+        Self {
+            raw: RawBox::from_float(val),
+            _marker: PhantomData,
+        }
+    }
+
+    #[inline]
+    #[allow(private_bounds)]
+    pub fn new_inline<T: InlineStorable>(val: T) -> Self {
+        Self::from_raw_value(RawValue::store(T::TAG, val))
+    }
+
+    #[inline]
+    #[allow(private_bounds)]
+    pub fn new_gc<T: GcStorable>(gc: Gc<'gc, T>) -> Self {
+        let ptr = Gc::as_ptr(gc);
+        Self::from_raw_value(RawValue::store(T::TAG, ptr))
+    }
+
+    #[inline]
+    pub fn make_int(val: i64, mc: &Mutation<'gc>) -> Self {
+        if val >= i32::MIN as i64 && val <= i32::MAX as i64 {
+            Value::new_inline(val as i32)
+        } else {
+            Value::new_gc(Gc::new(mc, val))
+        }
+    }
+}
+
+impl<'gc> Value<'gc> {
+    #[inline]
+    pub fn is_float(self) -> bool {
+        self.raw.is_float()
+    }
+
+    #[inline]
+    #[allow(private_bounds)]
+    pub fn is<T: Storable>(self) -> bool {
+        self.tag() == Some(T::TAG)
+    }
+}
+
+impl<'gc> Value<'gc> {
+    #[inline]
+    pub fn as_float(self) -> Option<f64> {
+        self.raw.float().copied()
+    }
+
+    #[inline]
+    #[allow(private_bounds)]
+    pub fn as_inline<T: InlineStorable>(self) -> Option<T> {
+        if self.is::<T>() {
+            Some(unsafe {
+                let rv = self.raw.value().unwrap_unchecked();
+                T::from_val(rv)
+            })
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    #[allow(private_bounds)]
+    pub fn as_gc<T: GcStorable>(self) -> Option<Gc<'gc, T>> {
+        if self.is::<T>() {
+            Some(unsafe {
+                let rv = self.raw.value().unwrap_unchecked();
+                let ptr: *const T = <*const T as RawStore>::from_val(rv);
+                Gc::from_ptr(ptr)
+            })
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    pub fn to_bits(self) -> u64 {
+        self.raw.to_bits()
+    }
+
+    #[inline]
+    pub fn as_num(self) -> Option<NixNum> {
+        if let Some(i) = self.as_inline::<i32>() {
+            Some(NixNum::Int(i as i64))
+        } else if let Some(gc_i) = self.as_gc::<i64>() {
+            Some(NixNum::Int(*gc_i))
+        } else {
+            self.as_float().map(NixNum::Float)
+        }
+    }
+
+    #[inline]
+    pub fn restrict(self) -> Result<StrictValue<'gc>, Gc<'gc, Thunk<'gc>>> {
+        if let Some(thunk) = self.as_gc::<Thunk<'gc>>() {
+            Err(thunk)
+        } else {
+            Ok(StrictValue(self))
+        }
+    }
+
+    #[inline]
+    pub fn ty(self) -> NixType {
+        if self.is_float() {
+            NixType::Float
+        } else if self.is::<i32>() || self.is::<i64>() {
+            NixType::Int
+        } else if self.is::<bool>() {
+            NixType::Bool
+        } else if self.is::<Null>() {
+            NixType::Null
+        } else if self.is::<StringId>() {
+            NixType::String
+        } else if self.is::<PrimOp>() {
+            NixType::PrimOp
+        } else if self.is::<NixString>() {
+            NixType::String
+        } else if self.is::<Path>() {
+            NixType::Path
+        } else if self.is::<AttrSet>() {
+            NixType::AttrSet
+        } else if self.is::<List>() {
+            NixType::List
+        } else if self.is::<Thunk>() {
+            NixType::Thunk
+        } else if self.is::<Closure>() {
+            NixType::Closure
+        } else if self.is::<PrimOpApp>() {
+            NixType::PrimOpApp
+        } else {
+            unreachable!("value has no recognized type tag")
+        }
+    }
+
+    #[inline]
+    #[allow(private_bounds)]
+    pub fn expect_inline<T: InlineStorable>(self) -> Result<T, NixType> {
+        self.as_inline::<T>().ok_or_else(|| self.ty())
+    }
+
+    #[inline]
+    #[allow(private_bounds)]
+    pub fn expect_gc<T: GcStorable>(self) -> Result<Gc<'gc, T>, NixType> {
+        self.as_gc::<T>().ok_or_else(|| self.ty())
+    }
+
+    #[inline]
+    pub fn expect_num(self) -> Result<NixNum, NixType> {
+        self.as_num().ok_or_else(|| self.ty())
+    }
+
+    #[inline]
+    pub fn expect_bool(self) -> Result<bool, NixType> {
+        self.as_inline::<bool>().ok_or_else(|| self.ty())
+    }
+
+    #[inline]
+    pub fn expect_float(self) -> Result<f64, NixType> {
+        self.as_float().ok_or_else(|| self.ty())
+    }
+}
+
+#[derive(Copy, Clone, Default)]
+#[repr(transparent)]
+pub struct StaticValue(Value<'static>);
+
+impl<'gc> From<StaticValue> for Value<'gc> {
+    #[inline]
+    fn from(value: StaticValue) -> Self {
+        // SAFETY: StaticValue is guaranteed to not contain any `Gc`.
+        unsafe { std::mem::transmute::<Value<'static>, Value<'gc>>(value.0) }
+    }
+}
+
+impl StaticValue {
+    #[inline]
+    pub fn new_float(val: f64) -> Self {
+        Self(Value::new_float(val))
+    }
+    #[inline]
+    #[allow(private_bounds)]
+    pub fn new_inline<T: InlineStorable>(val: T) -> Self {
+        Self(Value::new_inline(val))
+    }
+    #[inline]
+    pub fn new_primop(id: BuiltinId, arity: u8, dispatch_ip: u32) -> Self {
+        Self(Value::new_inline(PrimOp {
+            id,
+            arity,
+            dispatch_ip,
+        }))
+    }
+    #[inline]
+    pub fn is_float(self) -> bool {
+        self.0.is_float()
+    }
+    #[inline]
+    #[allow(private_bounds)]
+    pub fn is<T: InlineStorable>(self) -> bool {
+        self.0.is::<T>()
+    }
+    #[inline]
+    pub fn as_float(self) -> Option<f64> {
+        self.0.as_float()
+    }
+    #[inline]
+    #[allow(private_bounds)]
+    pub fn as_inline<T: InlineStorable>(self) -> Option<T> {
+        self.0.as_inline::<T>()
+    }
+    #[inline]
+    pub fn to_bits(self) -> u64 {
+        self.0.raw.to_bits()
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub struct Null;
+impl RawStore for Null {
+    fn to_val(self, value: &mut RawValue) {
+        value.set_data([0; 6]);
+    }
+    fn from_val(_: &RawValue) -> Self {
+        Self
+    }
+}
+
+impl RawStore for StringId {
+    fn to_val(self, value: &mut RawValue) {
+        (self.0.to_usize() as u32).to_val(value);
+    }
+    fn from_val(value: &RawValue) -> Self {
+        Self(
+            SymbolU32::try_from_usize(u32::from_val(value) as usize)
+                .expect("failed to read StringId from Value"),
+        )
+    }
+}
+
+/// A canonicalized absolute path. Inline value carrying an interned
+/// `StringId` whose contents are the path's absolute, dot-resolved form.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct Path(pub StringId);
+
+impl RawStore for Path {
+    fn to_val(self, value: &mut RawValue) {
+        self.0.to_val(value);
+    }
+    fn from_val(value: &RawValue) -> Self {
+        Self(StringId::from_val(value))
+    }
+}
+
+#[derive(Collect)]
+#[collect(require_static)]
+pub struct NixString {
+    data: Box<str>,
+    context: StringContext,
+}
+
+impl NixString {
+    pub fn new(s: impl Into<Box<str>>) -> Self {
+        Self {
+            data: s.into(),
+            context: StringContext::new(),
+        }
+    }
+
+    /// Construct a `NixString` whose `context` is already sorted+deduped.
+    /// The caller is responsible for invariant maintenance.
+    pub fn with_context(s: impl Into<Box<str>>, context: StringContext) -> Self {
+        Self {
+            data: s.into(),
+            context,
+        }
+    }
+
+    pub fn as_str(&self) -> &str {
+        &self.data
+    }
+
+    pub fn context(&self) -> &StringContext {
+        &self.context
+    }
+
+    pub fn has_context(&self) -> bool {
+        !self.context.is_empty()
+    }
+}
+
+impl fmt::Debug for NixString {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.data, f)
+    }
+}
+
+#[derive(Collect, Debug, Default)]
+#[collect(no_drop)]
+pub struct AttrSet<'gc> {
+    pub entries: SmallVec<[(StringId, Value<'gc>); 4]>,
+}
+
+impl<'gc> AttrSet<'gc> {
+    pub fn from_sorted_unchecked(entries: SmallVec<[(StringId, Value<'gc>); 4]>) -> Self {
+        debug_assert!(entries.is_sorted_by_key(|(key, _)| *key));
+        Self { entries }
+    }
+
+    pub fn lookup(&self, key: StringId) -> Option<Value<'gc>> {
+        self.entries
+            .binary_search_by_key(&key, |(k, _)| *k)
+            .ok()
+            .map(|i| self.entries[i].1)
+    }
+
+    pub fn has(&self, key: StringId) -> bool {
+        self.entries.binary_search_by_key(&key, |(k, _)| *k).is_ok()
+    }
+
+    pub fn merge(&self, other: &Self, mc: &Mutation<'gc>) -> Gc<'gc, Self> {
+        use std::cmp::Ordering::*;
+
+        debug_assert!(self.entries.is_sorted_by_key(|(key, _)| *key));
+        debug_assert!(other.entries.is_sorted_by_key(|(key, _)| *key));
+
+        let mut entries = SmallVec::new();
+        let mut i = 0;
+        let mut j = 0;
+        while i < self.entries.len() && j < other.entries.len() {
+            match self.entries[i].0.cmp(&other.entries[j].0) {
+                Less => {
+                    entries.push(self.entries[i]);
+                    i += 1;
+                }
+                Greater => {
+                    entries.push(other.entries[j]);
+                    j += 1;
+                }
+                Equal => {
+                    entries.push(other.entries[j]);
+                    i += 1;
+                    j += 1;
+                }
+            }
+        }
+        entries.extend(other.entries[j..].iter().cloned());
+        entries.extend(self.entries[i..].iter().cloned());
+
+        debug_assert!(entries.is_sorted_by_key(|(key, _)| *key));
+
+        Gc::new(mc, AttrSet { entries })
+    }
+}
+
+#[derive(Collect, Debug, Default)]
+#[repr(transparent)]
+#[collect(no_drop)]
+pub struct List<'gc> {
+    pub inner: RefLock<SmallVec<[Value<'gc>; 4]>>,
+}
+
+impl<'gc> List<'gc> {
+    pub fn new(mc: &Mutation<'gc>, data: SmallVec<[Value<'gc>; 4]>) -> Gc<'gc, Self> {
+        Gc::new(
+            mc,
+            Self {
+                inner: RefLock::new(data),
+            },
+        )
+    }
+
+    pub fn new_gc(mc: &Mutation<'gc>) -> Gc<'gc, Self> {
+        Gc::new(mc, Self::default())
+    }
+}
+
+impl<'gc> Unlock for List<'gc> {
+    type Unlocked = RefCell<SmallVec<[Value<'gc>; 4]>>;
+    unsafe fn unlock_unchecked(&self) -> &Self::Unlocked {
+        unsafe { self.inner.unlock_unchecked() }
+    }
+}
+
+pub type Thunk<'gc> = RefLock<ThunkState<'gc>>;
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub enum ThunkState<'gc> {
+    Pending { ip: usize, env: GcEnv<'gc> },
+    Apply { func: Value<'gc>, arg: Value<'gc> },
+    Blackhole,
+    Evaluated(StrictValue<'gc>),
+}
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub struct Env<'gc> {
+    pub locals: SmallVec<[Value<'gc>; 4]>,
+    pub prev: Option<GcEnv<'gc>>,
+}
+pub type GcEnv<'gc> = GcRefLock<'gc, Env<'gc>>;
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub struct WithEnv<'gc> {
+    pub env: Value<'gc>,
+    pub prev: Option<GcWithEnv<'gc>>,
+}
+pub type GcWithEnv<'gc> = Gc<'gc, WithEnv<'gc>>;
+
+impl<'gc> Env<'gc> {
+    pub fn empty() -> Self {
+        Env {
+            locals: SmallVec::new(),
+            prev: None,
+        }
+    }
+
+    pub fn with_arg(arg: Value<'gc>, n_locals: u32, prev: Gc<'gc, RefLock<Env<'gc>>>) -> Self {
+        let mut locals = smallvec::smallvec![Value::default(); 1 + n_locals as usize];
+        locals[0] = arg;
+        Env {
+            locals,
+            prev: Some(prev),
+        }
+    }
+}
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub struct Closure<'gc> {
+    pub ip: u32,
+    pub n_locals: u32,
+    pub env: Gc<'gc, RefLock<Env<'gc>>>,
+    pub pattern: Option<Gc<'gc, PatternInfo>>,
+}
+
+#[derive(Collect, Debug)]
+#[collect(require_static)]
+pub struct PatternInfo {
+    pub required: SmallVec<[StringId; 4]>,
+    pub optional: SmallVec<[StringId; 4]>,
+    pub ellipsis: bool,
+    pub param_spans: Box<[(StringId, u32)]>,
+}
+
+#[repr(packed, Rust)]
+#[derive(Clone, Copy, Debug, Collect)]
+#[collect(require_static)]
+pub struct PrimOp {
+    pub id: BuiltinId,
+    pub arity: u8,
+    pub dispatch_ip: u32,
+}
+
+impl RawStore for PrimOp {
+    fn to_val(self, value: &mut RawValue) {
+        let bytes = self.dispatch_ip.to_le_bytes();
+        value.set_data([
+            self.id as u8,
+            self.arity,
+            bytes[0],
+            bytes[1],
+            bytes[2],
+            bytes[3],
+        ]);
+    }
+    fn from_val(value: &RawValue) -> Self {
+        let [id, arity, bytes @ ..] = *value.data();
+        Self {
+            id: BuiltinId::try_from(id).expect("invalid BuiltinId"),
+            arity,
+            dispatch_ip: u32::from_le_bytes(bytes),
+        }
+    }
+}
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub struct PrimOpApp<'gc> {
+    pub primop: PrimOp,
+    pub arity: u8,
+    pub args: [Value<'gc>; 3],
+}
+
+#[derive(Copy, Clone, Default, Collect)]
+#[repr(transparent)]
+#[collect(no_drop)]
+pub struct StrictValue<'gc>(Value<'gc>);
+
+impl<'gc> StrictValue<'gc> {
+    #[inline]
+    pub fn relax(self) -> Value<'gc> {
+        self.0
+    }
+}
+
+impl<'gc> Deref for StrictValue<'gc> {
+    type Target = Value<'gc>;
+    #[inline]
+    fn deref(&self) -> &Value<'gc> {
+        &self.0
+    }
+}
+
+impl fmt::Debug for StrictValue<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.0, f)
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Collect)]
+#[collect(require_static)]
+pub enum NixType {
+    Int,
+    Float,
+    Bool,
+    Null,
+    String,
+    Path,
+    AttrSet,
+    List,
+    Thunk,
+    Closure,
+    PrimOp,
+    PrimOpApp,
+}
+
+impl NixType {
+    pub fn display(self) -> &'static str {
+        use NixType::*;
+        match self {
+            Int => "an integer",
+            Float => "a float",
+            Bool => "a boolean",
+            Null => "null",
+            String => "a string",
+            Path => "a path",
+            AttrSet => "a set",
+            List => "a list",
+            Thunk => "a thunk",
+            Closure => "a function",
+            PrimOp => "a built-in function",
+            PrimOpApp => "a partially applied built-in function",
+        }
+    }
+}
+
+impl std::fmt::Display for NixType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.display())
+    }
+}
+
+pub enum NixNum {
+    Int(i64),
+    Float(f64),
+}

fix-vm/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "fix-vm"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+gc-arena = { workspace = true }
+hashbrown = { workspace = true }
+smallvec = { workspace = true }
+sysinfo = { version = "0.38", default-features = false, features = ["system"] }
+
+fix-bytecode = { path = "../fix-bytecode" }
+fix-error = { path = "../fix-error" }
+fix-lang = { path = "../fix-lang" }
+fix-runtime = { path = "../fix-runtime" }
+
+[features]
+tailcall = []

fix-vm/src/dispatch_tailcall.rs

@@ -0,0 +1,304 @@
+#![cfg(feature = "tailcall")]
+
+use gc_arena::Mutation;
+
+use crate::{Break, BytecodeReader, Step, Vm, VmRuntimeCtx};
+
+pub(crate) enum TailResult {
+    YieldFuel(u32),
+    Done,
+    LoadFile,
+}
+
+pub(crate) type OpFn<'gc, C> = extern "rust-preserve-none" fn(
+    &mut Vm<'gc>,
+    &Mutation<'gc>,
+    &mut C,
+    &[u8],
+    &DispatchTable<'gc, C>,
+    u32,
+    u32,
+) -> TailResult;
+
+pub(crate) struct DispatchTable<'gc, C: VmRuntimeCtx>(pub(crate) [OpFn<'gc, C>; 256]);
+
+extern "rust-preserve-none" fn op_illegal<'gc, C: VmRuntimeCtx>(
+    _vm: &mut Vm<'gc>,
+    _mc: &Mutation<'gc>,
+    _ctx: &mut C,
+    _bc: &[u8],
+    _table: &DispatchTable<'gc, C>,
+    pc: u32,
+    _fuel: u32,
+) -> TailResult {
+    panic!("illegal opcode at pc = {pc}");
+}
+
+macro_rules! tail_dispatch_after {
+    ($result:expr, $new_pc:expr, $vm:ident, $mc:ident, $ctx:ident, $bc:ident, $table:ident, $fuel:ident) => {{
+        match $result {
+            Step::Continue(()) | Step::Break(Break::Force) => {}
+            Step::Break(Break::LoadFile) => return TailResult::LoadFile,
+            Step::Break(Break::Done) => return TailResult::Done,
+        }
+        let new_pc: u32 = $new_pc;
+        if $fuel == 0 {
+            return TailResult::YieldFuel(new_pc);
+        }
+        let next_op = $bc[new_pc as usize] as usize;
+        become $table.0[next_op]($vm, $mc, $ctx, $bc, $table, new_pc, $fuel - 1)
+    }};
+}
+
+macro_rules! tail_fn {
+    ($name:ident, ()) => {
+        extern "rust-preserve-none" fn $name<'gc, C: VmRuntimeCtx>(
+            vm: &mut Vm<'gc>,
+            mc: &Mutation<'gc>,
+            ctx: &mut C,
+            bc: &[u8],
+            table: &DispatchTable<'gc, C>,
+            pc: u32,
+            fuel: u32,
+        ) -> TailResult {
+            let result = crate::instructions::$name(vm);
+            tail_dispatch_after!(result, pc + 1, vm, mc, ctx, bc, table, fuel)
+        }
+    };
+    ($name:ident, (reader)) => {
+        extern "rust-preserve-none" fn $name<'gc, C: VmRuntimeCtx>(
+            vm: &mut Vm<'gc>,
+            mc: &Mutation<'gc>,
+            ctx: &mut C,
+            bc: &[u8],
+            table: &DispatchTable<'gc, C>,
+            pc: u32,
+            fuel: u32,
+        ) -> TailResult {
+            let mut reader = BytecodeReader::from_after_op(bc, pc as usize);
+            let result = crate::instructions::$name(vm, &mut reader);
+            tail_dispatch_after!(result, reader.pc() as u32, vm, mc, ctx, bc, table, fuel)
+        }
+    };
+    ($name:ident, (reader, mc)) => {
+        extern "rust-preserve-none" fn $name<'gc, C: VmRuntimeCtx>(
+            vm: &mut Vm<'gc>,
+            mc: &Mutation<'gc>,
+            ctx: &mut C,
+            bc: &[u8],
+            table: &DispatchTable<'gc, C>,
+            pc: u32,
+            fuel: u32,
+        ) -> TailResult {
+            let mut reader = BytecodeReader::from_after_op(bc, pc as usize);
+            let result = crate::instructions::$name(vm, &mut reader, mc);
+            tail_dispatch_after!(result, reader.pc() as u32, vm, mc, ctx, bc, table, fuel)
+        }
+    };
+    ($name:ident, (ctx, reader, mc)) => {
+        extern "rust-preserve-none" fn $name<'gc, C: VmRuntimeCtx>(
+            vm: &mut Vm<'gc>,
+            mc: &Mutation<'gc>,
+            ctx: &mut C,
+            bc: &[u8],
+            table: &DispatchTable<'gc, C>,
+            pc: u32,
+            fuel: u32,
+        ) -> TailResult {
+            let mut reader = BytecodeReader::from_after_op(bc, pc as usize);
+            let result = crate::instructions::$name(vm, ctx, &mut reader, mc);
+            tail_dispatch_after!(result, reader.pc() as u32, vm, mc, ctx, bc, table, fuel)
+        }
+    };
+    ($name:ident, (ctx)) => {
+        extern "rust-preserve-none" fn $name<'gc, C: VmRuntimeCtx>(
+            vm: &mut Vm<'gc>,
+            mc: &Mutation<'gc>,
+            ctx: &mut C,
+            bc: &[u8],
+            table: &DispatchTable<'gc, C>,
+            pc: u32,
+            fuel: u32,
+        ) -> TailResult {
+            let result = crate::instructions::$name(vm, ctx);
+            tail_dispatch_after!(result, pc + 1, vm, mc, ctx, bc, table, fuel)
+        }
+    };
+}
+
+tail_fn!(op_push_smi, (reader));
+tail_fn!(op_push_bigint, (reader, mc));
+tail_fn!(op_push_float, (reader));
+tail_fn!(op_push_string, (reader));
+tail_fn!(op_push_null, ());
+tail_fn!(op_push_true, ());
+tail_fn!(op_push_false, ());
+
+tail_fn!(op_load_local, (reader));
+tail_fn!(op_load_outer, (reader));
+tail_fn!(op_store_local, (reader, mc));
+tail_fn!(op_alloc_locals, (reader, mc));
+
+tail_fn!(op_make_thunk, (reader, mc));
+tail_fn!(op_make_closure, (reader, mc));
+tail_fn!(op_make_pattern_closure, (reader, mc));
+
+tail_fn!(op_call, (ctx, reader, mc));
+tail_fn!(op_dispatch_primop, (ctx, reader, mc));
+tail_fn!(op_return, (ctx, reader, mc));
+
+tail_fn!(op_make_attrs, (ctx, reader, mc));
+tail_fn!(op_make_empty_attrs, ());
+tail_fn!(op_select_static, (ctx, reader, mc));
+tail_fn!(op_select_dynamic, (ctx, reader, mc));
+tail_fn!(op_has_attr_path_static, (ctx, reader, mc));
+tail_fn!(op_has_attr_path_dynamic, (ctx, reader, mc));
+tail_fn!(op_jump_if_select_failed, (reader));
+tail_fn!(op_jump_if_select_succeeded, (reader));
+tail_fn!(op_has_attr_static, (reader, mc));
+tail_fn!(op_has_attr_dynamic, (ctx, reader, mc));
+tail_fn!(op_has_attr_resolve, ());
+
+tail_fn!(op_make_list, (ctx, reader, mc));
+tail_fn!(op_make_empty_list, ());
+
+tail_fn!(op_add, (ctx, reader, mc));
+tail_fn!(op_sub, (reader, mc));
+tail_fn!(op_mul, (reader, mc));
+tail_fn!(op_div, (reader, mc));
+tail_fn!(op_eq, (ctx, reader, mc));
+tail_fn!(op_neq, (ctx, reader, mc));
+tail_fn!(op_lt, (ctx, reader, mc));
+tail_fn!(op_gt, (ctx, reader, mc));
+tail_fn!(op_leq, (ctx, reader, mc));
+tail_fn!(op_geq, (ctx, reader, mc));
+tail_fn!(op_concat, (reader, mc));
+tail_fn!(op_update, (reader, mc));
+
+tail_fn!(op_neg, (reader, mc));
+tail_fn!(op_not, (reader, mc));
+
+tail_fn!(op_jump_if_false, (reader, mc));
+tail_fn!(op_jump_if_true, (reader, mc));
+tail_fn!(op_jump, (reader));
+
+tail_fn!(op_coerce_to_string, (reader, mc));
+
+tail_fn!(op_concat_strings, (ctx, reader, mc));
+tail_fn!(op_resolve_path, (ctx, reader, mc));
+
+tail_fn!(op_assert, (ctx, reader, mc));
+
+tail_fn!(op_lookup_with, (ctx, reader, mc));
+
+tail_fn!(op_load_builtins, ());
+tail_fn!(op_load_builtin, (reader));
+
+tail_fn!(op_load_repl_binding, (reader));
+tail_fn!(op_load_scoped_binding, (ctx, reader, mc));
+
+macro_rules! table {
+    ($($variant:ident => $fn:ident),* $(,)?) => {
+        impl<'gc, C: VmRuntimeCtx> DispatchTable<'gc, C> {
+            pub(crate) const NEW: Self = {
+                let mut arr: [OpFn<'gc, C>; 256] = [op_illegal; 256];
+                $( arr[fix_bytecode::Op::$variant as usize] = $fn; )*
+                DispatchTable(arr)
+            };
+        }
+
+        // Exhaustiveness check: fails to compile if `fix_bytecode::Op` gains,
+        // loses, or renames a variant that isn't wired up above.
+        #[allow(dead_code)]
+        const _: fn(fix_bytecode::Op) = |op| match op {
+            $( fix_bytecode::Op::$variant => (), )*
+        };
+    };
+}
+
+table! {
+    PushSmi               => op_push_smi,
+    PushBigInt            => op_push_bigint,
+    PushFloat             => op_push_float,
+    PushString            => op_push_string,
+    PushNull              => op_push_null,
+    PushTrue              => op_push_true,
+    PushFalse             => op_push_false,
+
+    LoadLocal             => op_load_local,
+    LoadOuter             => op_load_outer,
+    StoreLocal            => op_store_local,
+    AllocLocals           => op_alloc_locals,
+
+    MakeThunk             => op_make_thunk,
+    MakeClosure           => op_make_closure,
+    MakePatternClosure    => op_make_pattern_closure,
+
+    Call                  => op_call,
+    DispatchPrimOp        => op_dispatch_primop,
+    Return                => op_return,
+
+    MakeAttrs             => op_make_attrs,
+    MakeEmptyAttrs        => op_make_empty_attrs,
+    SelectStatic          => op_select_static,
+    SelectDynamic         => op_select_dynamic,
+    HasAttrPathStatic     => op_has_attr_path_static,
+    HasAttrPathDynamic    => op_has_attr_path_dynamic,
+    HasAttrStatic         => op_has_attr_static,
+    HasAttrDynamic        => op_has_attr_dynamic,
+    HasAttrResolve        => op_has_attr_resolve,
+    JumpIfSelectSucceeded => op_jump_if_select_succeeded,
+    JumpIfSelectFailed    => op_jump_if_select_failed,
+
+    MakeList              => op_make_list,
+    MakeEmptyList         => op_make_empty_list,
+
+    OpAdd                 => op_add,
+    OpSub                 => op_sub,
+    OpMul                 => op_mul,
+    OpDiv                 => op_div,
+    OpEq                  => op_eq,
+    OpNeq                 => op_neq,
+    OpLt                  => op_lt,
+    OpGt                  => op_gt,
+    OpLeq                 => op_leq,
+    OpGeq                 => op_geq,
+    OpConcat              => op_concat,
+    OpUpdate              => op_update,
+
+    OpNeg                 => op_neg,
+    OpNot                 => op_not,
+
+    JumpIfFalse           => op_jump_if_false,
+    JumpIfTrue            => op_jump_if_true,
+    Jump                  => op_jump,
+
+    CoerceToString        => op_coerce_to_string,
+
+    ConcatStrings         => op_concat_strings,
+    ResolvePath           => op_resolve_path,
+
+    Assert                => op_assert,
+
+    LookupWith            => op_lookup_with,
+
+    LoadBuiltins          => op_load_builtins,
+    LoadBuiltin           => op_load_builtin,
+
+    LoadReplBinding       => op_load_repl_binding,
+    LoadScopedBinding     => op_load_scoped_binding,
+
+    Illegal               => op_illegal,
+}
+
+pub(crate) fn run_tailcall<'gc, C: VmRuntimeCtx>(
+    vm: &mut Vm<'gc>,
+    mc: &Mutation<'gc>,
+    ctx: &mut C,
+    bc: &[u8],
+    pc: u32,
+) -> TailResult {
+    let table = &DispatchTable::<'gc, C>::NEW;
+    let op = bc[pc as usize] as usize;
+    table.0[op](vm, mc, ctx, bc, table, pc, Vm::DEFAULT_FUEL_AMOUNT)
+}

fix-vm/src/instructions/arithmetic.rs

@@ -0,0 +1,319 @@
+use std::cmp::Ordering;
+
+use fix_runtime::*;
+use gc_arena::{Gc, Mutation, RefLock};
+
+use crate::{BytecodeReader, NixNum, Step, VmError, VmRuntimeCtx};
+
+#[inline(always)]
+pub(crate) fn op_add<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let (lhs, rhs) = m.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+    // if the LHS is a path, the result is a path obtained by
+    // canonicalizing the concatenated string. RHS may be a path or a
+    // string. (A `string + path` keeps the string-typed result, handled
+    // by the next branch.)
+    if lhs.is::<Path>() {
+        let (Some(ls), Some(rs)) = (ctx.get_string_or_path(lhs), ctx.get_string_or_path(rhs))
+        else {
+            return m.finish_err(fix_error::Error::eval_error(format!(
+                "cannot append {} to a path",
+                rhs.ty()
+            )));
+        };
+        let combined = format!("{ls}{rs}");
+        let canon = canon_path_str(&combined);
+        let sid = ctx.intern_string(canon);
+        m.push(Value::new_inline(fix_runtime::Path(sid)));
+        return Step::Continue(());
+    }
+    if let (Some(ls), Some(rs)) = (ctx.get_string(lhs), ctx.get_string_or_path(rhs)) {
+        let merged = ctx
+            .get_string_context(lhs)
+            .merge(ctx.get_string_context(rhs));
+        let ns = Gc::new(
+            mc,
+            crate::NixString::with_context(format!("{ls}{rs}"), merged),
+        );
+        m.push(Value::new_gc(ns));
+        return Step::Continue(());
+    }
+    let res = numeric_binop(lhs, rhs, mc, i64::wrapping_add, |a, b| a + b);
+    match res {
+        Ok(val) => {
+            m.push(val);
+            Step::Continue(())
+        }
+        Err(e) => m.finish_vm_err(e),
+    }
+}
+
+#[inline(always)]
+pub(crate) fn op_sub<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    op_arith(m, reader, mc, i64::wrapping_sub, |a, b| a - b)
+}
+
+#[inline(always)]
+pub(crate) fn op_mul<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    op_arith(m, reader, mc, i64::wrapping_mul, |a, b| a * b)
+}
+
+#[inline(always)]
+fn op_arith<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+    int_op: fn(i64, i64) -> i64,
+    float_op: fn(f64, f64) -> f64,
+) -> Step {
+    let (lhs, rhs) = m.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+    let res = numeric_binop(lhs, rhs, mc, int_op, float_op);
+    match res {
+        Ok(val) => {
+            m.push(val);
+            Step::Continue(())
+        }
+        Err(e) => m.finish_vm_err(e),
+    }
+}
+
+#[inline(always)]
+pub(crate) fn op_div<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let (lhs, rhs) = m.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+    match (get_num(lhs), get_num(rhs)) {
+        (_, Some(NixNum::Int(0))) | (_, Some(NixNum::Float(0.))) => {
+            return m.finish_vm_err(VmError::Uncatchable(fix_error::Error::eval_error(
+                "division by zero",
+            )));
+        }
+        _ => {}
+    }
+    let res = numeric_binop(lhs, rhs, mc, |a, b| a / b, |a, b| a / b);
+    match res {
+        Ok(val) => {
+            m.push(val);
+            Step::Continue(())
+        }
+        Err(e) => m.finish_vm_err(e),
+    }
+}
+
+#[inline(always)]
+pub(crate) fn op_eq<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let (lhs, rhs) = m.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+    crate::primops::start_eq(m, ctx, reader, mc, lhs, rhs, false)
+}
+
+#[inline(always)]
+pub(crate) fn op_neq<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let (lhs, rhs) = m.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+    crate::primops::start_eq(m, ctx, reader, mc, lhs, rhs, true)
+}
+
+#[inline(always)]
+pub(crate) fn op_lt<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    compare_values(m, ctx, reader, mc, Ordering::is_lt)
+}
+
+#[inline(always)]
+pub(crate) fn op_gt<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    compare_values(m, ctx, reader, mc, Ordering::is_gt)
+}
+
+#[inline(always)]
+pub(crate) fn op_leq<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    compare_values(m, ctx, reader, mc, Ordering::is_le)
+}
+
+#[inline(always)]
+pub(crate) fn op_geq<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    compare_values(m, ctx, reader, mc, Ordering::is_ge)
+}
+
+fn compare_values<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+    pred: fn(Ordering) -> bool,
+) -> Step {
+    let (lhs, rhs) = m.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+    match compare_values_inner(m, ctx, pred, lhs, rhs) {
+        Ok(()) => Step::Continue(()),
+        Err(e) => m.finish_vm_err(e),
+    }
+}
+
+#[inline(always)]
+pub(crate) fn op_concat<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let (l, r) = m.force_and_retry::<(Gc<List>, Gc<List>)>(reader, mc)?;
+    let mut items = smallvec::SmallVec::new();
+    items.extend_from_slice(&l.inner.borrow());
+    items.extend_from_slice(&r.inner.borrow());
+    m.push(Value::new_gc(Gc::new(
+        mc,
+        crate::List {
+            inner: RefLock::new(items),
+        },
+    )));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_update<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let (l, r) = m.force_and_retry::<(Gc<AttrSet>, Gc<AttrSet>)>(reader, mc)?;
+    m.push(Value::new_gc(l.merge(&r, mc)));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_neg<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let rhs = m.force_and_retry::<NixNum>(reader, mc)?;
+    match rhs {
+        NixNum::Int(int) => m.push(Value::make_int(-int, mc)),
+        NixNum::Float(float) => m.push(Value::new_float(-float)),
+    }
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_not<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let rhs = m.force_and_retry::<bool>(reader, mc)?;
+    m.push(Value::new_inline(!rhs));
+    Step::Continue(())
+}
+
+fn compare_values_inner<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &impl VmRuntimeCtx,
+    pred: fn(Ordering) -> bool,
+    lhs: StrictValue<'gc>,
+    rhs: StrictValue<'gc>,
+) -> crate::VmResult<()> {
+    if let (Some(a), Some(b)) = (get_num(lhs), get_num(rhs)) {
+        let ord = match (a, b) {
+            (NixNum::Int(a), NixNum::Int(b)) => a.cmp(&b),
+            (NixNum::Float(a), NixNum::Float(b)) => a.partial_cmp(&b).unwrap_or(Ordering::Less),
+            (NixNum::Int(a), NixNum::Float(b)) => {
+                (a as f64).partial_cmp(&b).unwrap_or(Ordering::Less)
+            }
+            (NixNum::Float(a), NixNum::Int(b)) => {
+                a.partial_cmp(&(b as f64)).unwrap_or(Ordering::Less)
+            }
+        };
+        m.push(Value::new_inline(pred(ord)));
+        return Ok(());
+    }
+    if let (Some(a), Some(b)) = (ctx.get_string(lhs), ctx.get_string(rhs)) {
+        m.push(Value::new_inline(pred(a.cmp(b))));
+        return Ok(());
+    }
+    if let (Some(a), Some(b)) = (lhs.as_inline::<Path>(), rhs.as_inline::<Path>()) {
+        let a = ctx.resolve_string(a.0);
+        let b = ctx.resolve_string(b.0);
+        m.push(Value::new_inline(pred(a.cmp(b))));
+        return Ok(());
+    }
+    // TODO: compare other types
+    Err(crate::vm_err(format!(
+        "cannot compare {} with {}",
+        lhs.ty(),
+        rhs.ty()
+    )))
+}
+
+pub(crate) fn get_num(val: StrictValue<'_>) -> Option<NixNum> {
+    if let Some(i) = val.as_inline::<i32>() {
+        Some(NixNum::Int(i64::from(i)))
+    } else if let Some(gc_i) = val.as_gc::<i64>() {
+        Some(NixNum::Int(*gc_i))
+    } else {
+        val.as_float().map(NixNum::Float)
+    }
+}
+
+#[inline]
+fn numeric_binop<'gc>(
+    lhs: StrictValue<'gc>,
+    rhs: StrictValue<'gc>,
+    mc: &Mutation<'gc>,
+    int_op: fn(i64, i64) -> i64,
+    float_op: fn(f64, f64) -> f64,
+) -> crate::VmResult<Value<'gc>> {
+    match (get_num(lhs), get_num(rhs)) {
+        (Some(NixNum::Int(a)), Some(NixNum::Int(b))) => Ok(Value::make_int(int_op(a, b), mc)),
+        (Some(NixNum::Float(a)), Some(NixNum::Float(b))) => Ok(Value::new_float(float_op(a, b))),
+        (Some(NixNum::Int(a)), Some(NixNum::Float(b))) => {
+            Ok(Value::new_float(float_op(a as f64, b)))
+        }
+        (Some(NixNum::Float(a)), Some(NixNum::Int(b))) => {
+            Ok(Value::new_float(float_op(a, b as f64)))
+        }
+        _ => Err(crate::vm_err(format!(
+            "cannot perform arithmetic on non-numbers: {:?}",
+            (lhs.ty(), rhs.ty())
+        ))),
+    }
+}

fix-vm/src/instructions/calls.rs

@@ -0,0 +1,181 @@
+use fix_bytecode::PrimOpPhase;
+use fix_error::Error;
+use fix_runtime::{resolve_operand, *};
+use gc_arena::{Gc, Mutation, RefLock};
+
+use crate::{
+    BytecodeReader, CallFrame, Closure, Env, ForceMode, Step, ThunkState, VmRuntimeCtx,
+    VmRuntimeCtxExt,
+};
+
+#[inline(always)]
+pub(crate) fn call<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+    arg: Value<'gc>,
+    resume_pc: usize,
+) -> Step {
+    let func = m.force_and_retry::<StrictValue>(reader, mc)?;
+    if m.call_depth() > 10000 {
+        return m.finish_err(Error::eval_error("stack overflow; max-call-depth exceeded"));
+    }
+    m.inc_call_depth();
+    if let Some(closure) = func.as_gc::<Closure>() {
+        if closure.pattern.is_some() {
+            // FIXME: better DX...
+            m.push(func.relax());
+            m.push(arg);
+            m.push_call_frame(CallFrame {
+                pc: resume_pc,
+                thunk: None,
+                env: m.env(),
+            });
+            reader.set_pc(PrimOpPhase::CallPattern.ip() as usize);
+            return Step::Continue(());
+        }
+
+        let ip = closure.ip;
+        let n_locals = closure.n_locals;
+        let env = closure.env;
+        let new_env = Gc::new(mc, RefLock::new(Env::with_arg(arg, n_locals, env)));
+        m.push_call_frame(CallFrame {
+            pc: resume_pc,
+            thunk: None,
+            env: m.env(),
+        });
+        reader.set_pc(ip as usize);
+        m.set_env(new_env);
+    } else if let Some(primop) = func.as_inline::<PrimOp>() {
+        if primop.arity == 1 {
+            m.push(arg);
+            m.push_call_frame(CallFrame {
+                pc: resume_pc,
+                thunk: None,
+                env: m.env(),
+            });
+            reader.set_pc(primop.dispatch_ip as usize)
+        } else {
+            let app = PrimOpApp {
+                primop,
+                arity: primop.arity - 1,
+                args: [arg, Value::default(), Value::default()],
+            };
+            m.push(Value::new_gc(Gc::new(mc, app)));
+        }
+    } else if let Some(app) = func.as_gc::<PrimOpApp>() {
+        if app.arity == 1 {
+            for i in 0..app.primop.arity - 1 {
+                m.push(app.args[i as usize]);
+            }
+            m.push(arg);
+            m.push_call_frame(CallFrame {
+                pc: resume_pc,
+                thunk: None,
+                env: m.env(),
+            });
+            reader.set_pc(app.primop.dispatch_ip as usize)
+        } else {
+            let position = (app.primop.arity - app.arity) as usize;
+            let mut new_app = PrimOpApp {
+                arity: app.arity - 1,
+                ..*app
+            };
+            new_app.args[position] = arg;
+            m.push(Value::new_gc(Gc::new(mc, new_app)))
+        }
+    } else if let Some(attrs) = func.as_gc::<AttrSet>()
+        && let Some(functor) = attrs.lookup(m.functor_sym())
+    {
+        // f arg  =>  (f.__functor f) arg
+        //
+        // Stage the work for `CallFunctor1` so retries during force are
+        // safe: the stack invariant `[..., orig_arg, self, functor]`
+        // holds every time control re-enters phase 1.
+        m.dec_call_depth();
+        m.push_call_frame(CallFrame {
+            pc: resume_pc,
+            thunk: None,
+            env: m.env(),
+        });
+        m.push(arg);
+        m.push(func.relax());
+        m.push(functor);
+        reader.set_pc(PrimOpPhase::CallFunctor1.ip() as usize);
+        return Step::Continue(());
+    } else {
+        return m.finish_err(Error::eval_error(format!(
+            "attempt to call something which is not a function but {}",
+            func.ty()
+        )));
+    }
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_call<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let arg = resolve_operand(&reader.read_operand_data(), mc, ctx, m);
+    let pc = reader.pc();
+    m.call(reader, mc, arg, pc)
+}
+
+#[inline(always)]
+pub(crate) fn op_return<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    let Some(CallFrame {
+        pc: ret_pc,
+        thunk,
+        env,
+    }) = m.pop_call_frame()
+    else {
+        match m.force_mode() {
+            ForceMode::AsIs => return m.finish_ok(ctx.convert_value(val.relax())),
+            ForceMode::Shallow => {
+                m.push(val.relax());
+                reader.set_pc(PrimOpPhase::ForceResultShallow.ip() as usize);
+                return Step::Continue(());
+            }
+            ForceMode::Deep => {
+                m.push(val.relax());
+                m.push(val.relax());
+                m.push_call_frame(CallFrame {
+                    pc: PrimOpPhase::ForceResultDeepFinish.ip() as usize,
+                    thunk: None,
+                    env: m.env(),
+                });
+                m.inc_call_depth();
+                reader.set_pc(PrimOpPhase::DeepSeq.ip() as usize);
+                return Step::Continue(());
+            }
+        }
+    };
+    reader.set_pc(ret_pc);
+    if let Some(outer_thunk) = thunk {
+        *outer_thunk.borrow_mut(mc) = ThunkState::Evaluated(val);
+    } else {
+        m.dec_call_depth();
+        m.push(val.relax())
+    }
+    m.set_env(env);
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_dispatch_primop<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    crate::primops::dispatch_primop(m, ctx, reader, mc)
+}

fix-vm/src/instructions/closures.rs

@@ -0,0 +1,93 @@
+use fix_runtime::Machine;
+use gc_arena::{Gc, Mutation, RefLock};
+
+use crate::{BytecodeReader, Step, ThunkState, Value};
+
+#[inline(always)]
+pub(crate) fn op_make_thunk<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let entry_point = reader.read_u32();
+    let thunk = Gc::new(
+        mc,
+        RefLock::new(ThunkState::Pending {
+            ip: entry_point as usize,
+            env: m.env(),
+        }),
+    );
+    m.push(Value::new_gc(thunk));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_make_closure<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let entry_point = reader.read_u32();
+    let n_locals = reader.read_u32();
+    let closure = Gc::new(
+        mc,
+        crate::Closure {
+            ip: entry_point,
+            n_locals,
+            env: m.env(),
+            pattern: None,
+        },
+    );
+    m.push(Value::new_gc(closure));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_make_pattern_closure<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let entry_point = reader.read_u32();
+    let n_locals = reader.read_u32();
+    let req_count = reader.read_u16() as usize;
+    let opt_count = reader.read_u16() as usize;
+    let has_ellipsis = reader.read_u8() != 0;
+
+    let mut required = smallvec::SmallVec::new();
+    for _ in 0..req_count {
+        required.push(reader.read_string_id());
+    }
+    let mut optional = smallvec::SmallVec::new();
+    for _ in 0..opt_count {
+        optional.push(reader.read_string_id());
+    }
+    let total = req_count + opt_count;
+    let mut param_spans = Vec::with_capacity(total);
+    for _ in 0..total {
+        let name = reader.read_string_id();
+        let span_id = reader.read_u32();
+        param_spans.push((name, span_id));
+    }
+
+    let pattern = Gc::new(
+        mc,
+        crate::PatternInfo {
+            required,
+            optional,
+            ellipsis: has_ellipsis,
+            param_spans: param_spans.into_boxed_slice(),
+        },
+    );
+    let closure = Gc::new(
+        mc,
+        crate::Closure {
+            ip: entry_point,
+            n_locals,
+            env: m.env(),
+            pattern: Some(pattern),
+        },
+    );
+    m.push(Value::new_gc(closure));
+    Step::Continue(())
+}

fix-vm/src/instructions/collections.rs

@@ -0,0 +1,337 @@
+use fix_error::Error;
+use fix_lang::StringId;
+use fix_runtime::{Machine, MachineExt, NixType, resolve_operand};
+use gc_arena::{Gc, RefLock};
+use smallvec::SmallVec;
+
+use crate::{
+    AttrSet, BytecodeReader, List, Step, StrictValue, Value, VmRuntimeCtx, VmRuntimeCtxExt,
+};
+
+#[inline(always)]
+pub(crate) fn op_make_attrs<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let static_count = reader.read_u32() as usize;
+    let dynamic_count = reader.read_u32() as usize;
+
+    for i in 0..dynamic_count {
+        let depth = dynamic_count - 1 - i;
+        m.force_slot_to_pc(depth, reader, mc, reader.inst_start_pc())?;
+    }
+
+    let mut dyn_keys: SmallVec<[_; 2]> = SmallVec::with_capacity(dynamic_count);
+    for i in 0..dynamic_count {
+        let depth = dynamic_count - 1 - i;
+        let key_val = m.peek_forced(depth);
+        let key_sid = match ctx.get_string_id(key_val) {
+            Ok(id) => Some(id),
+            Err(NixType::Null) => None,
+            Err(got) => return m.finish_type_err(NixType::String, got),
+        };
+        dyn_keys.push(key_sid);
+    }
+
+    m.drop_n(dynamic_count);
+
+    let mut kv: SmallVec<[(crate::StringId, Value); 4]> =
+        SmallVec::with_capacity(static_count + dynamic_count);
+
+    for _ in 0..static_count {
+        let key = reader.read_string_id();
+        let val = resolve_operand(&reader.read_operand_data(), mc, ctx, m);
+        let _span_id = reader.read_u32();
+        kv.push((key, val));
+    }
+
+    for key in dyn_keys {
+        let val = resolve_operand(&reader.read_operand_data(), mc, ctx, m);
+        let _span_id = reader.read_u32();
+        if let Some(key) = key {
+            kv.push((key, val))
+        }
+    }
+
+    kv.sort_by_key(|(k, _)| *k);
+    let attrs = Gc::new(mc, AttrSet::from_sorted_unchecked(kv));
+    m.push(Value::new_gc(attrs));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_make_empty_attrs<'gc, M: Machine<'gc>>(m: &mut M) -> Step {
+    m.push(m.empty_attrs());
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_select_static<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let _span_id = reader.read_u32();
+    let key = reader.read_string_id();
+
+    let attrset = m.force_and_retry::<Gc<AttrSet>>(reader, mc)?;
+
+    match attrset.lookup(key) {
+        Some(v) => {
+            m.push(v);
+        }
+        None => return select_skip(m, key, ctx, reader),
+    }
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_select_dynamic<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let _span_id = reader.read_u32();
+
+    let (attrset, key_val) = m.force_and_retry::<(Gc<AttrSet>, StrictValue)>(reader, mc)?;
+
+    let key_sid = match ctx.get_string_id(key_val) {
+        Ok(id) => id,
+        Err(got) => return m.finish_type_err(NixType::String, got),
+    };
+
+    match attrset.lookup(key_sid) {
+        Some(v) => {
+            m.push(v);
+        }
+        None => return select_skip(m, key_sid, ctx, reader),
+    }
+    Step::Continue(())
+}
+
+/// Skip the rest of a **Select** attrpath after a missing attribute.
+/// Only recognises Select opcodes and jumps; encountering any other
+/// opcode means we've reached the end of the select sequence and
+/// should report the missing-attribute error.
+fn select_skip<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    key: StringId,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    use fix_bytecode::Op::*;
+    loop {
+        match reader.read_op() {
+            SelectStatic => {
+                reader.set_pc(reader.pc() + 4 + 4);
+            }
+            SelectDynamic => {
+                reader.set_pc(reader.pc() + 4);
+            }
+            JumpIfSelectSucceeded => {
+                reader.set_pc(reader.pc() + 4);
+                break Step::Continue(());
+            }
+            JumpIfSelectFailed => {
+                let offset = reader.read_i32();
+                reader.set_pc(((reader.pc() as isize) + (offset as isize)) as usize);
+            }
+            _ => {
+                let name = ctx.resolve_string(key);
+                return m.finish_err(Error::eval_error(format!("attribute '{name}' missing")));
+            }
+        }
+    }
+}
+
+/// Skip the rest of a **HasAttr** attrpath after an intermediate
+/// lookup failed. Only recognises HasAttr opcodes and jumps.
+fn has_attr_skip(reader: &mut BytecodeReader<'_>) -> Step {
+    use fix_bytecode::Op::*;
+    loop {
+        match reader.read_op() {
+            HasAttrPathStatic => {
+                reader.set_pc(reader.pc() + 4 + 4);
+            }
+            HasAttrPathDynamic => {
+                reader.set_pc(reader.pc() + 4);
+            }
+            HasAttrStatic => {
+                reader.set_pc(reader.pc() + 4);
+                break Step::Continue(());
+            }
+            JumpIfSelectFailed => {
+                let offset = reader.read_i32();
+                reader.set_pc(((reader.pc() as isize) + (offset as isize)) as usize);
+            }
+            HasAttrDynamic => {
+                break Step::Continue(());
+            }
+            HasAttrResolve => {
+                reader.set_pc(reader.pc() - 1);
+                break Step::Continue(());
+            }
+            other => {
+                unreachable!("unexpected opcode {:?} in has_attr_skip", other as u8)
+            }
+        }
+    }
+}
+
+#[inline(always)]
+pub(crate) fn op_has_attr_path_static<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    _ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let _span_id = reader.read_u32();
+    let key = reader.read_string_id();
+
+    let current = m.force_and_retry::<StrictValue>(reader, mc)?;
+
+    match current
+        .as_gc::<AttrSet>()
+        .and_then(|attrs| attrs.lookup(key))
+    {
+        Some(v) => {
+            m.push(v);
+        }
+        None => return has_attr_skip(reader),
+    }
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_has_attr_path_dynamic<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let _span_id = reader.read_u32();
+
+    let (current, key_val) = m.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+
+    let key_sid = match ctx.get_string_id(key_val) {
+        Ok(id) => id,
+        Err(got) => return m.finish_type_err(NixType::String, got),
+    };
+
+    match current
+        .as_gc::<AttrSet>()
+        .and_then(|attrs| attrs.lookup(key_sid))
+    {
+        Some(v) => {
+            m.push(v);
+        }
+        None => return has_attr_skip(reader),
+    }
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_jump_if_select_failed<'gc, M: Machine<'gc>>(
+    _m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    // No-op
+    let _offset = reader.read_i32();
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_jump_if_select_succeeded<'gc, M: Machine<'gc>>(
+    _m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    let offset = reader.read_i32();
+    reader.set_pc(((reader.pc() as isize) + (offset as isize)) as usize);
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_has_attr_static<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let key = reader.read_string_id();
+    let current = m.force_and_retry::<StrictValue>(reader, mc)?;
+
+    m.push(Value::new_inline(
+        current
+            .as_gc::<AttrSet>()
+            .and_then(|attrs| attrs.lookup(key))
+            .is_some(),
+    ));
+    // Skip HasAttrResolve
+    reader.set_pc(reader.pc() + 1);
+
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_has_attr_dynamic<'gc, M: MachineExt<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let (current, dyn_key) = m.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+
+    let key_sid = match ctx.get_string_id(dyn_key) {
+        Ok(id) => id,
+        Err(got) => return m.finish_type_err(NixType::String, got),
+    };
+
+    m.push(Value::new_inline(
+        current
+            .as_gc::<AttrSet>()
+            .and_then(|attrs| attrs.lookup(key_sid))
+            .is_some(),
+    ));
+    // Skip HasAttrResolve
+    reader.set_pc(reader.pc() + 1);
+
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_has_attr_resolve<'gc, M: Machine<'gc>>(m: &mut M) -> Step {
+    // If we reach here, has_attr check has failed, push false (AttrSet is already popped)
+    m.push(Value::new_inline(false));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_make_list<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let count = reader.read_u32() as usize;
+    let mut items: SmallVec<[Value; 4]> = SmallVec::with_capacity(count);
+    for _ in 0..count {
+        items.push(resolve_operand(&reader.read_operand_data(), mc, ctx, m));
+    }
+    let list = Gc::new(
+        mc,
+        List {
+            inner: RefLock::new(items),
+        },
+    );
+    m.push(Value::new_gc(list));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_make_empty_list<'gc, M: Machine<'gc>>(m: &mut M) -> Step {
+    m.push(m.empty_list());
+    Step::Continue(())
+}

fix-vm/src/instructions/control.rs

@@ -0,0 +1,58 @@
+use fix_error::Error;
+use fix_runtime::*;
+use gc_arena::Mutation;
+
+use crate::{BytecodeReader, Step, VmRuntimeCtx};
+
+#[inline(always)]
+pub(crate) fn op_jump_if_false<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let offset = reader.read_i32();
+    let cond = m.force_and_retry::<StrictValue>(reader, mc)?;
+    if cond.as_inline::<bool>() == Some(false) {
+        reader.set_pc(((reader.pc() as isize) + (offset as isize)) as usize);
+    }
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_jump_if_true<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let offset = reader.read_i32();
+    let cond = m.force_and_retry::<StrictValue>(reader, mc)?;
+    if cond.as_inline::<bool>() == Some(true) {
+        reader.set_pc(((reader.pc() as isize) + (offset as isize)) as usize);
+    }
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_jump<'gc, M: Machine<'gc>>(_m: &mut M, reader: &mut BytecodeReader<'_>) -> Step {
+    let offset = reader.read_i32();
+    reader.set_pc(((reader.pc() as isize) + (offset as isize)) as usize);
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_assert<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let raw_id = reader.read_string_id();
+    let raw = ctx.resolve_string(raw_id);
+    let _span_id = reader.read_u32();
+    let assertion = m.force_and_retry::<bool>(reader, mc)?;
+    if !assertion {
+        // FIXME: use catchable error
+        return m.finish_err(Error::eval_error(format!("assertion '{raw}' failed")));
+    }
+    Step::Continue(())
+}

fix-vm/src/instructions/literals.rs

@@ -0,0 +1,63 @@
+use fix_runtime::Machine;
+use gc_arena::{Gc, Mutation};
+
+use crate::{BytecodeReader, Step, Value};
+
+#[inline(always)]
+pub(crate) fn op_push_smi<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    let val = reader.read_i32();
+    m.push(Value::new_inline(val));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_push_bigint<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let val = reader.read_i64();
+    m.push(Value::new_gc(Gc::new(mc, val)));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_push_float<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    let val = reader.read_f64();
+    m.push(Value::new_float(val));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_push_string<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    let sid = reader.read_string_id();
+    m.push(Value::new_inline(sid));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_push_null<'gc, M: Machine<'gc>>(m: &mut M) -> Step {
+    m.push(Value::new_inline(crate::Null));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_push_true<'gc, M: Machine<'gc>>(m: &mut M) -> Step {
+    m.push(Value::new_inline(true));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_push_false<'gc, M: Machine<'gc>>(m: &mut M) -> Step {
+    m.push(Value::new_inline(false));
+    Step::Continue(())
+}

fix-vm/src/instructions/misc.rs

@@ -0,0 +1,179 @@
+use std::path::PathBuf;
+
+use fix_bytecode::PrimOpPhase;
+use fix_error::Error;
+use fix_lang::{BUILTINS, BuiltinId, StringId};
+use fix_runtime::{
+    AttrSet, Machine, MachineExt, NixString, Path, StrictValue, StringContext, canon_path_str,
+};
+
+use crate::{BytecodeReader, PrimOp, Step, Value, VmRuntimeCtx, VmRuntimeCtxExt};
+
+#[inline(always)]
+pub(crate) fn op_load_builtins<'gc, M: Machine<'gc>>(m: &mut M) -> Step {
+    m.push(m.builtins());
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_load_builtin<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    let Ok(id) = BuiltinId::try_from(reader.read_u8())
+        .map_err(|err| panic!("unknown builtin id: {}", err.number));
+    m.push(Value::new_inline(PrimOp {
+        id,
+        arity: BUILTINS[id as usize].1,
+        dispatch_ip: PrimOpPhase::entry_for_builtin(id).ip(),
+    }));
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_load_repl_binding<'gc, M: Machine<'gc>>(
+    _m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    let _name = reader.read_string_id();
+    todo!("LoadReplBinding");
+}
+
+#[inline(always)]
+pub(crate) fn op_load_scoped_binding<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    _mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let slot_id = reader.read_u32();
+    let name = reader.read_string_id();
+    let scope = m.scope_slot(slot_id);
+    let Some(attrs) = scope.as_gc::<AttrSet>() else {
+        return m.finish_err(Error::eval_error("internal: scope slot is not an attrset"));
+    };
+    match attrs.lookup(name) {
+        Some(val) => {
+            m.push(val);
+            Step::Continue(())
+        }
+        None => m.finish_err(Error::eval_error(format!(
+            "scoped binding '{}' not found",
+            ctx.resolve_string(name)
+        ))),
+    }
+}
+
+#[inline(always)]
+pub(crate) fn op_coerce_to_string<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    if val.is::<StringId>() || val.is::<NixString>() {
+        m.push(val.relax());
+    } else if let Some(p) = val.as_inline::<Path>() {
+        // Coercing a path to a string yields the canonical path text.
+        // FIXME: copy to store
+        m.push(Value::new_inline(p.0));
+    } else {
+        todo!("coerce other types to string: {:?}", val.ty());
+    }
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_concat_strings<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let count = reader.read_u16() as usize;
+    let _force_string = reader.read_u8() != 0;
+
+    let mut total_len = 0;
+    let mut has_any_context = false;
+    for i in 0..count {
+        let val = m.peek_forced(count - 1 - i);
+        let s = ctx.get_string(val).expect("coerced");
+        total_len += s.len();
+        if !ctx.get_string_context(val).is_empty() {
+            has_any_context = true;
+        }
+    }
+
+    let mut result = String::with_capacity(total_len);
+    let mut merged = StringContext::new();
+    for i in 0..count {
+        let val = m.peek_forced(count - 1 - i);
+        let s = ctx.get_string(val).expect("coerced");
+        result.push_str(s);
+        if has_any_context {
+            let ctx = ctx.get_string_context(val);
+            if !ctx.is_empty() {
+                merged = merged.merge(ctx);
+            }
+        }
+    }
+
+    m.drop_n(count);
+
+    if merged.is_empty() {
+        let sid = ctx.intern_string(result);
+        m.push(Value::new_inline(sid));
+    } else {
+        let ns = gc_arena::Gc::new(mc, NixString::with_context(result, merged));
+        m.push(Value::new_gc(ns));
+    }
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_resolve_path<'gc, M: MachineExt<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    let path_val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    let dir_id = reader.read_string_id();
+    // Already a path: keep as-is. ResolvePath is idempotent on paths.
+    if let Some(p) = path_val.as_inline::<Path>() {
+        m.push(Value::new_inline(p));
+        return Step::Continue(());
+    }
+    let path = match ctx.get_string(path_val) {
+        Some(s) => s.to_owned(),
+        None => {
+            return m.finish_err(Error::eval_error(format!(
+                "expected a string for path, got {}",
+                path_val.ty()
+            )));
+        }
+    };
+    let resolved = match resolve_path_str(ctx.resolve_string(dir_id), &path) {
+        Ok(s) => s,
+        Err(e) => return m.finish_err(e),
+    };
+    let sid = ctx.intern_string(resolved);
+    m.push(Value::new_inline(Path(sid)));
+    Step::Continue(())
+}
+
+fn resolve_path_str(current_dir: &str, path: &str) -> Result<String, Box<Error>> {
+    let raw = if path.starts_with('/') {
+        return Ok(canon_path_str(path));
+    } else if let Some(rest) = path.strip_prefix("~/") {
+        let mut dir =
+            std::env::home_dir().ok_or_else(|| Error::eval_error("home dir not defined"))?;
+        dir.push(rest);
+        dir
+    } else {
+        let mut dir = PathBuf::from(current_dir);
+        dir.push(path);
+        dir
+    };
+    Ok(canon_path_str(&raw))
+}

fix-vm/src/instructions/mod.rs

@@ -0,0 +1,19 @@
+pub(crate) mod arithmetic;
+pub(crate) mod calls;
+pub(crate) mod closures;
+pub(crate) mod collections;
+pub(crate) mod control;
+pub(crate) mod literals;
+pub(crate) mod misc;
+pub(crate) mod variables;
+pub(crate) mod with_scope;
+
+pub(crate) use arithmetic::*;
+pub(crate) use calls::*;
+pub(crate) use closures::*;
+pub(crate) use collections::*;
+pub(crate) use control::*;
+pub(crate) use literals::*;
+pub(crate) use misc::*;
+pub(crate) use variables::*;
+pub(crate) use with_scope::*;

fix-vm/src/instructions/variables.rs

@@ -0,0 +1,56 @@
+use fix_runtime::Machine;
+
+use crate::{BytecodeReader, Mutation, Step, Value};
+
+#[inline(always)]
+pub(crate) fn op_load_local<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    let idx = reader.read_u32() as usize;
+    m.push(m.env().borrow().locals[idx]);
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_load_outer<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    let layer = reader.read_u8();
+    let idx = reader.read_u32() as usize;
+    let mut cur = m.env();
+    for _ in 0..layer {
+        let prev = cur.borrow().prev.expect("LoadOuter: env chain too short");
+        cur = prev;
+    }
+    let val = cur.borrow().locals[idx];
+    m.push(val);
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_store_local<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let idx = reader.read_u32() as usize;
+    let val = m.pop();
+    m.env().borrow_mut(mc).locals[idx] = val;
+    Step::Continue(())
+}
+
+#[inline(always)]
+pub(crate) fn op_alloc_locals<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let count = reader.read_u32() as usize;
+    m.env()
+        .borrow_mut(mc)
+        .locals
+        .extend(std::iter::repeat_n(Value::default(), count));
+    Step::Continue(())
+}

fix-vm/src/instructions/with_scope.rs

@@ -0,0 +1,75 @@
+use fix_error::Error;
+use fix_lang::Symbol;
+use fix_runtime::{resolve_operand, *};
+use smallvec::SmallVec;
+
+use crate::{Break, BytecodeReader, CallFrame, Step, VmRuntimeCtx};
+
+#[inline(always)]
+pub(crate) fn op_lookup_with<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &gc_arena::Mutation<'gc>,
+) -> Step {
+    #[allow(clippy::unwrap_used)]
+    let counter = m.peek_forced(0).as_inline::<i32>().unwrap();
+
+    let name = reader.read_string_id();
+    let n = reader.read_u8();
+    let mut namespaces = SmallVec::<[_; 2]>::new();
+    for _ in 0..n {
+        namespaces.push(resolve_operand(&reader.read_operand_data(), mc, ctx, m));
+    }
+
+    let resume_pc = reader.inst_start_pc();
+    let namespace = match namespaces[counter as usize].restrict() {
+        Ok(val) => val,
+        Err(thunk) => {
+            let mut state = thunk.borrow_mut(mc);
+            match *state {
+                ThunkState::Pending { ip, env } => {
+                    *state = ThunkState::Blackhole;
+                    m.push_call_frame(CallFrame {
+                        thunk: Some(thunk),
+                        pc: resume_pc,
+                        env: m.env(),
+                    });
+                    m.set_env(env);
+                    reader.set_pc(ip);
+                    return Step::Break(Break::Force);
+                }
+                ThunkState::Evaluated(v) => v,
+                ThunkState::Apply { func, arg } => {
+                    m.push_call_frame(CallFrame {
+                        thunk: Some(thunk),
+                        pc: resume_pc,
+                        env: m.env(),
+                    });
+                    m.push(func);
+                    return m.call(reader, mc, arg, resume_pc);
+                }
+                ThunkState::Blackhole => {
+                    return m.finish_err(Error::eval_error("infinite recursion encountered"));
+                }
+            }
+        }
+    };
+
+    if let Some(val) = namespace
+        .as_gc::<AttrSet>()
+        .and_then(|attrs| attrs.lookup(name))
+    {
+        m.replace(0, val);
+    } else if counter + 1 == n as i32 {
+        return m.finish_err(Error::eval_error(format!(
+            "undefined variable '{}'",
+            Symbol::from(ctx.resolve_string(name))
+        )));
+    } else {
+        m.replace(0, Value::new_inline(counter + 1));
+        reader.set_pc(resume_pc);
+    }
+
+    Step::Continue(())
+}

fix-vm/src/lib.rs

@@ -0,0 +1,575 @@
+#![warn(clippy::unwrap_used)]
+#![cfg_attr(feature = "tailcall", expect(incomplete_features))]
+#![cfg_attr(
+    feature = "tailcall",
+    feature(explicit_tail_calls, rust_preserve_none_cc)
+)]
+
+use std::path::PathBuf;
+
+use fix_bytecode::{InstructionPtr, PrimOpPhase};
+use fix_error::{Error, Result, Source};
+use fix_lang::{BUILTINS, BuiltinId, StringId};
+use gc_arena::metrics::Pacing;
+use gc_arena::{Arena, Collect, Gc, Mutation, RefLock, Rootable};
+use hashbrown::HashMap;
+use smallvec::SmallVec;
+
+#[cfg(feature = "tailcall")]
+mod dispatch_tailcall;
+pub use fix_runtime::*;
+mod instructions;
+mod primops;
+
+type VmResult<T> = std::result::Result<T, VmError>;
+
+#[derive(Collect)]
+#[collect(no_drop)]
+pub struct Vm<'gc> {
+    stack: Vec<Value<'gc>>,
+    call_stack: Vec<CallFrame<'gc>>,
+    call_depth: usize,
+    #[allow(dead_code)]
+    #[collect(require_static)]
+    error_context: Vec<ErrorFrame>,
+
+    env: GcEnv<'gc>,
+
+    import_cache: HashMap<PathBuf, Value<'gc>>,
+    scope_slots: Vec<Value<'gc>>,
+
+    builtins: Value<'gc>,
+    empty_list: Value<'gc>,
+    empty_attrs: Value<'gc>,
+
+    force_mode: ForceMode,
+
+    #[collect(require_static)]
+    result: Option<Result<fix_lang::Value>>,
+
+    #[collect(require_static)]
+    pending_load: Option<PendingLoad>,
+
+    functor_sym: StringId,
+}
+
+fn init_builtins<'gc>(mc: &Mutation<'gc>, ctx: &mut impl VmRuntimeCtx) -> Value<'gc> {
+    let mut entries = SmallVec::with_capacity(BUILTINS.len());
+
+    for (idx, &(name, arity)) in BUILTINS.iter().enumerate() {
+        let id = BuiltinId::try_from(idx as u8).expect("infallible");
+        let name = name.strip_prefix("__").unwrap_or(name);
+        let name = ctx.intern_string(name);
+        let dispatch_ip = PrimOpPhase::entry_for_builtin(id).ip();
+        entries.push((
+            name,
+            Value::new_inline(PrimOp {
+                id,
+                arity,
+                dispatch_ip,
+            }),
+        ));
+    }
+
+    let consts = [
+        (
+            "__currentSystem",
+            Value::new_inline(ctx.intern_string("x86_64-linux")),
+        ),
+        ("__langVersion", Value::new_inline(6i32)),
+        (
+            "__nixVersion",
+            Value::new_inline(ctx.intern_string("2.24.0")),
+        ),
+        (
+            "__storeDir",
+            Value::new_inline(ctx.intern_string("/nix/store")),
+        ),
+        ("__nixPath", Value::new_gc(Gc::new(mc, List::default()))),
+        ("null", Value::new_inline(Null)),
+        ("true", Value::new_inline(true)),
+        ("false", Value::new_inline(false)),
+    ];
+
+    for (name, val) in consts {
+        let name = name.strip_prefix("__").unwrap_or(name);
+        let name = ctx.intern_string(name);
+        entries.push((name, val));
+    }
+
+    let self_ref_thunk = Gc::new(mc, RefLock::new(ThunkState::Blackhole));
+    let sym = ctx.intern_string("builtins");
+    entries.push((sym, Value::new_gc(self_ref_thunk)));
+
+    entries.sort_by_key(|(k, _)| *k);
+
+    let builtins_set = Gc::new(mc, AttrSet::from_sorted_unchecked(entries));
+    let builtins_value = Value::new_gc(builtins_set);
+    *self_ref_thunk.borrow_mut(mc) =
+        ThunkState::Evaluated(builtins_value.restrict().expect("builtins is not a thunk"));
+    builtins_value
+}
+
+impl<'gc> Vm<'gc> {
+    fn new(force_mode: ForceMode, mc: &Mutation<'gc>, ctx: &mut impl VmRuntimeCtx) -> Self {
+        let builtins = init_builtins(mc, ctx);
+        Vm {
+            stack: Vec::with_capacity(8192),
+            call_stack: Vec::with_capacity(1024),
+            call_depth: 0,
+            error_context: Vec::with_capacity(1024),
+
+            env: Gc::new(mc, RefLock::new(Env::empty())),
+
+            import_cache: HashMap::new(),
+            scope_slots: Vec::new(),
+
+            builtins,
+            empty_list: Value::new_gc(Gc::new(mc, List::default())),
+            empty_attrs: Value::new_gc(Gc::new(mc, AttrSet::default())),
+
+            force_mode,
+
+            result: None,
+            pending_load: None,
+
+            functor_sym: ctx.intern_string("__functor"),
+        }
+    }
+}
+
+impl<'gc> Machine<'gc> for Vm<'gc> {
+    #[inline(always)]
+    fn push(&mut self, val: Value<'gc>) {
+        self.stack.push(val);
+    }
+
+    #[inline(always)]
+    fn pop(&mut self) -> Value<'gc> {
+        self.stack.pop().expect("stack underflow")
+    }
+
+    #[inline(always)]
+    fn peek(&self, depth: usize) -> Value<'gc> {
+        *self
+            .stack
+            .get(self.stack.len() - depth - 1)
+            .expect("stack underflow")
+    }
+
+    #[inline(always)]
+    fn peek_forced(&self, depth: usize) -> StrictValue<'gc> {
+        self.stack
+            .get(self.stack.len() - depth - 1)
+            .expect("stack underflow")
+            .restrict()
+            .expect("forced")
+    }
+
+    #[inline(always)]
+    fn pop_forced(&mut self) -> StrictValue<'gc> {
+        self.stack
+            .pop()
+            .expect("stack underflow")
+            .restrict()
+            .expect("forced")
+    }
+
+    #[inline(always)]
+    fn replace(&mut self, depth: usize, val: Value<'gc>) {
+        let len = self.stack.len();
+        *self
+            .stack
+            .get_mut(len - depth - 1)
+            .expect("stack underflow") = val;
+    }
+
+    #[inline(always)]
+    fn drop_n(&mut self, depth: usize) {
+        self.stack.truncate(self.stack.len() - depth);
+    }
+
+    #[inline(always)]
+    fn stack_len(&self) -> usize {
+        self.stack.len()
+    }
+
+    #[inline(always)]
+    fn force_slot_to_pc(
+        &mut self,
+        depth: usize,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        resume_pc: usize,
+    ) -> Step {
+        let Some(thunk) = self.peek(depth).as_gc::<Thunk>() else {
+            return Step::Continue(());
+        };
+        let mut state = thunk.borrow_mut(mc);
+        match *state {
+            ThunkState::Pending { ip, env } => {
+                *state = ThunkState::Blackhole;
+                self.call_stack.push(CallFrame {
+                    thunk: Some(thunk),
+                    pc: resume_pc,
+                    env: self.env,
+                });
+                self.env = env;
+                reader.set_pc(ip);
+                Step::Break(Break::Force)
+            }
+            ThunkState::Evaluated(v) => {
+                self.replace(depth, v.relax());
+                Step::Continue(())
+            }
+            ThunkState::Apply { func, arg } => {
+                self.call_stack.push(CallFrame {
+                    thunk: Some(thunk),
+                    pc: resume_pc,
+                    env: self.env,
+                });
+                self.push(func);
+                self.call(reader, mc, arg, resume_pc)
+            }
+            ThunkState::Blackhole => {
+                self.finish_err(Error::eval_error("infinite recursion encountered"))
+            }
+        }
+    }
+
+    #[inline(always)]
+    fn call(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        arg: Value<'gc>,
+        resume_pc: usize,
+    ) -> Step {
+        instructions::call(self, reader, mc, arg, resume_pc)
+    }
+
+    #[inline(always)]
+    fn push_call_frame(&mut self, frame: CallFrame<'gc>) {
+        self.call_stack.push(frame);
+    }
+
+    #[inline(always)]
+    fn pop_call_frame(&mut self) -> Option<CallFrame<'gc>> {
+        self.call_stack.pop()
+    }
+
+    #[inline(always)]
+    fn call_depth(&self) -> usize {
+        self.call_depth
+    }
+
+    #[inline(always)]
+    fn inc_call_depth(&mut self) {
+        self.call_depth += 1;
+    }
+
+    #[inline(always)]
+    fn dec_call_depth(&mut self) {
+        self.call_depth -= 1;
+    }
+
+    #[inline(always)]
+    fn env(&self) -> GcEnv<'gc> {
+        self.env
+    }
+
+    #[inline(always)]
+    fn set_env(&mut self, env: GcEnv<'gc>) {
+        self.env = env;
+    }
+
+    #[inline(always)]
+    fn finish_ok(&mut self, val: fix_lang::Value) -> Step {
+        self.result = Some(Ok(val));
+        Step::Break(Break::Done)
+    }
+
+    #[inline(always)]
+    fn finish_err(&mut self, err: Box<Error>) -> Step {
+        self.result = Some(Err(err));
+        Step::Break(Break::Done)
+    }
+
+    #[inline(always)]
+    fn finish_type_err(&mut self, expected: NixType, got: NixType) -> Step {
+        self.result = Some(Err(Error::eval_error(format!(
+            "expected {expected}, got {got}"
+        ))));
+        Step::Break(Break::Done)
+    }
+
+    #[inline(always)]
+    fn builtins(&self) -> Value<'gc> {
+        self.builtins
+    }
+
+    #[inline(always)]
+    fn functor_sym(&self) -> StringId {
+        self.functor_sym
+    }
+
+    #[inline(always)]
+    fn empty_list(&self) -> Value<'gc> {
+        self.empty_list
+    }
+
+    #[inline(always)]
+    fn empty_attrs(&self) -> Value<'gc> {
+        self.empty_attrs
+    }
+
+    #[inline(always)]
+    fn force_mode(&self) -> ForceMode {
+        self.force_mode
+    }
+
+    #[inline(always)]
+    fn import_cache_get(&self, path: &std::path::Path) -> Option<Value<'gc>> {
+        self.import_cache.get(path).copied()
+    }
+
+    #[inline(always)]
+    fn import_cache_insert(&mut self, path: PathBuf, val: Value<'gc>) {
+        self.import_cache.insert(path, val);
+    }
+
+    #[inline(always)]
+    fn scope_slot(&self, idx: u32) -> Value<'gc> {
+        *self
+            .scope_slots
+            .get(idx as usize)
+            .expect("invalid scope slot")
+    }
+
+    #[inline(always)]
+    fn scope_slots_push(&mut self, val: Value<'gc>) -> u32 {
+        let idx = self.scope_slots.len() as u32;
+        self.scope_slots.push(val);
+        idx
+    }
+
+    #[inline(always)]
+    fn set_pending_load(&mut self, load: PendingLoad) {
+        self.pending_load = Some(load);
+    }
+}
+
+enum Action {
+    Continue { pc: usize },
+    Done(Result<fix_lang::Value>),
+    LoadFile(PendingLoad),
+}
+
+/// Compute initial heap size mirroring CppNix's strategy: 25% of physical RAM,
+/// clamped to [32 MiB, 384 MiB]. Used as `Pacing::min_sleep` so the collector
+/// defers the first cycle until the heap reaches this size.
+fn initial_heap_size() -> usize {
+    const MIN_SIZE: usize = 32 * 1024 * 1024;
+    const MAX_SIZE: usize = 384 * 1024 * 1024;
+
+    let mut sys = sysinfo::System::new();
+    sys.refresh_memory();
+    let total = sys.total_memory() as usize;
+    let quarter = total / 4;
+    quarter.clamp(MIN_SIZE, MAX_SIZE)
+}
+
+impl Vm<'_> {
+    pub fn run<C: VmContext>(
+        ctx: &mut C,
+        ip: InstructionPtr,
+        force_mode: ForceMode,
+    ) -> Result<fix_lang::Value> {
+        let (code, runtime) = ctx.split();
+        let mut arena: Arena<Rootable![Vm<'_>]> = Arena::new(|mc| Vm::new(force_mode, mc, runtime));
+        arena.metrics().set_pacing(Pacing {
+            min_sleep: initial_heap_size(),
+            ..Pacing::STOP_THE_WORLD
+        });
+
+        let mut pc = ip.0;
+        loop {
+            let bytecode = code.bytecode();
+            match arena.mutate_root(|mc, root| root.dispatch_batch(bytecode, runtime, pc, mc)) {
+                Action::Continue { pc: new_pc } => {
+                    pc = new_pc;
+                    if arena.metrics().allocation_debt() > 0.0 {
+                        arena.finish_cycle();
+                    }
+                }
+                Action::LoadFile(load) => {
+                    let source = match Source::new_file(load.path) {
+                        Ok(src) => src,
+                        Err(err) => break Err(Error::eval_error(format!("import failed: {err}"))),
+                    };
+                    let extra_scope = load.scope.map(|s| ExtraScope::ScopedImport {
+                        keys: s.keys,
+                        slot_id: s.slot_id,
+                    });
+                    let new_ip = match code.compile_with_scope(source, extra_scope, runtime) {
+                        Ok(ip) => ip,
+                        Err(err) => break Err(err),
+                    };
+                    pc = new_ip.0;
+                    arena.mutate_root(|mc, root| {
+                        root.env = Gc::new(mc, RefLock::new(Env::empty()));
+                    });
+                }
+                Action::Done(done) => break done,
+            }
+        }
+    }
+}
+
+impl<'gc> Vm<'gc> {
+    const DEFAULT_FUEL_AMOUNT: u32 = 1024;
+
+    #[inline(always)]
+    fn dispatch_batch<C: VmRuntimeCtx>(
+        &mut self,
+        bytecode: &[u8],
+        ctx: &mut C,
+        pc: usize,
+        mc: &Mutation<'gc>,
+    ) -> Action {
+        #[cfg(not(feature = "tailcall"))]
+        {
+            self.execute_batch(bytecode, ctx, pc, mc)
+        }
+        #[cfg(feature = "tailcall")]
+        {
+            use crate::dispatch_tailcall::{TailResult, run_tailcall};
+            match run_tailcall(self, mc, ctx, bytecode, pc as u32) {
+                TailResult::YieldFuel(new_pc) => Action::Continue {
+                    pc: new_pc as usize,
+                },
+                TailResult::Done => {
+                    Action::Done(self.result.take().expect("TailResult::Done without result"))
+                }
+                TailResult::LoadFile => Action::LoadFile(
+                    self.pending_load
+                        .take()
+                        .expect("TailResult::LoadFile without pending_load"),
+                ),
+            }
+        }
+    }
+
+    #[inline(always)]
+    #[cfg(not(feature = "tailcall"))]
+    fn execute_batch(
+        &mut self,
+        bytecode: &[u8],
+        ctx: &mut impl VmRuntimeCtx,
+        pc: usize,
+        mc: &Mutation<'gc>,
+    ) -> Action {
+        use fix_bytecode::Op::*;
+        use instructions::*;
+
+        let mut reader = BytecodeReader::new(bytecode, pc);
+        let mut fuel = Self::DEFAULT_FUEL_AMOUNT;
+
+        loop {
+            if fuel == 0 {
+                return Action::Continue { pc: reader.pc() };
+            }
+            fuel -= 1;
+
+            let op = reader.read_op();
+
+            let result = match op {
+                PushSmi => op_push_smi(self, &mut reader),
+                PushBigInt => op_push_bigint(self, &mut reader, mc),
+                PushFloat => op_push_float(self, &mut reader),
+                PushString => op_push_string(self, &mut reader),
+                PushNull => op_push_null(self),
+                PushTrue => op_push_true(self),
+                PushFalse => op_push_false(self),
+
+                LoadLocal => op_load_local(self, &mut reader),
+                LoadOuter => op_load_outer(self, &mut reader),
+                StoreLocal => op_store_local(self, &mut reader, mc),
+                AllocLocals => op_alloc_locals(self, &mut reader, mc),
+
+                MakeThunk => op_make_thunk(self, &mut reader, mc),
+                MakeClosure => op_make_closure(self, &mut reader, mc),
+                MakePatternClosure => op_make_pattern_closure(self, &mut reader, mc),
+
+                Call => op_call(self, ctx, &mut reader, mc),
+                DispatchPrimOp => op_dispatch_primop(self, ctx, &mut reader, mc),
+                Return => op_return(self, ctx, &mut reader, mc),
+
+                MakeAttrs => op_make_attrs(self, ctx, &mut reader, mc),
+                MakeEmptyAttrs => op_make_empty_attrs(self),
+                SelectStatic => op_select_static(self, ctx, &mut reader, mc),
+                SelectDynamic => op_select_dynamic(self, ctx, &mut reader, mc),
+                HasAttrPathStatic => op_has_attr_path_static(self, ctx, &mut reader, mc),
+                HasAttrPathDynamic => op_has_attr_path_dynamic(self, ctx, &mut reader, mc),
+                HasAttrStatic => op_has_attr_static(self, &mut reader, mc),
+                HasAttrDynamic => op_has_attr_dynamic(self, ctx, &mut reader, mc),
+                HasAttrResolve => op_has_attr_resolve(self),
+                JumpIfSelectFailed => op_jump_if_select_failed(self, &mut reader),
+                JumpIfSelectSucceeded => op_jump_if_select_succeeded(self, &mut reader),
+
+                MakeList => op_make_list(self, ctx, &mut reader, mc),
+                MakeEmptyList => op_make_empty_list(self),
+
+                OpAdd => op_add(self, ctx, &mut reader, mc),
+                OpSub => op_sub(self, &mut reader, mc),
+                OpMul => op_mul(self, &mut reader, mc),
+                OpDiv => op_div(self, &mut reader, mc),
+                OpEq => op_eq(self, ctx, &mut reader, mc),
+                OpNeq => op_neq(self, ctx, &mut reader, mc),
+                OpLt => op_lt(self, ctx, &mut reader, mc),
+                OpGt => op_gt(self, ctx, &mut reader, mc),
+                OpLeq => op_leq(self, ctx, &mut reader, mc),
+                OpGeq => op_geq(self, ctx, &mut reader, mc),
+                OpConcat => op_concat(self, &mut reader, mc),
+                OpUpdate => op_update(self, &mut reader, mc),
+
+                OpNeg => op_neg(self, &mut reader, mc),
+                OpNot => op_not(self, &mut reader, mc),
+
+                JumpIfFalse => op_jump_if_false(self, &mut reader, mc),
+                JumpIfTrue => op_jump_if_true(self, &mut reader, mc),
+                Jump => op_jump(self, &mut reader),
+
+                ConcatStrings => op_concat_strings(self, ctx, &mut reader, mc),
+                CoerceToString => op_coerce_to_string(self, &mut reader, mc),
+                ResolvePath => op_resolve_path(self, ctx, &mut reader, mc),
+
+                Assert => op_assert(self, ctx, &mut reader, mc),
+
+                LookupWith => op_lookup_with(self, ctx, &mut reader, mc),
+
+                LoadBuiltins => op_load_builtins(self),
+                LoadBuiltin => op_load_builtin(self, &mut reader),
+
+                LoadReplBinding => op_load_repl_binding(self, &mut reader),
+                LoadScopedBinding => op_load_scoped_binding(self, ctx, &mut reader, mc),
+
+                Illegal => unreachable!(),
+            };
+
+            match result {
+                Step::Continue(()) | Step::Break(Break::Force) => {}
+                Step::Break(Break::Done) => {
+                    return Action::Done(self.result.take().expect("Break::Done without result"));
+                }
+                Step::Break(Break::LoadFile) => {
+                    return Action::LoadFile(
+                        self.pending_load
+                            .take()
+                            .expect("Break::LoadFile without pending_load"),
+                    );
+                }
+            }
+        }
+    }
+}

fix-vm/src/primops/context.rs

@@ -0,0 +1,447 @@
+//! `builtins.hasContext`, `builtins.getContext`, `builtins.appendContext`,
+//! `builtins.unsafeDiscardStringContext`,
+//! `builtins.unsafeDiscardOutputDependency`.
+//!
+//! See `fix-runtime/src/string_context.rs` for the
+//! `StringContextElem` type.
+
+use fix_bytecode::PrimOpPhase;
+use fix_error::Error;
+use fix_lang::StringId;
+use fix_runtime::{
+    AttrSet, BytecodeReader, List as VmList, Machine, MachineExt, NixString, NixType, Step,
+    StrictValue, StringContext, StringContextElem, Value, VmRuntimeCtx, VmRuntimeCtxExt,
+};
+use gc_arena::{Gc, Mutation};
+use smallvec::SmallVec;
+
+pub fn has_context<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    if !val.is::<StringId>() && val.as_gc::<NixString>().is_none() {
+        return m.finish_type_err(NixType::String, val.ty());
+    }
+    let has_ctx = !ctx.get_string_context(val).is_empty();
+    m.return_from_primop(Value::new_inline(has_ctx), reader)
+}
+
+pub fn unsafe_discard_string_context<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    if let Some(sid) = val.as_inline::<StringId>() {
+        return m.return_from_primop(Value::new_inline(sid), reader);
+    }
+    let Some(ns) = val.as_gc::<NixString>() else {
+        return m.finish_type_err(NixType::String, val.ty());
+    };
+    let sid = ctx.intern_string(ns.as_str());
+    m.return_from_primop(Value::new_inline(sid), reader)
+}
+
+pub fn unsafe_discard_output_dependency<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    if let Some(sid) = val.as_inline::<StringId>() {
+        return m.return_from_primop(Value::new_inline(sid), reader);
+    }
+    let Some(ns) = val.as_gc::<NixString>() else {
+        return m.finish_type_err(NixType::String, val.ty());
+    };
+    if ns.context().is_empty() {
+        let sid = ctx.intern_string(ns.as_str());
+        return m.return_from_primop(Value::new_inline(sid), reader);
+    }
+
+    let mut new_ctx = StringContext::new();
+    for elem in ns.context() {
+        let replacement = match elem {
+            StringContextElem::DrvDeep { drv_path } => StringContextElem::Opaque {
+                path: drv_path.clone(),
+            },
+            other => other.clone(),
+        };
+        new_ctx.insert(replacement);
+    }
+
+    let s: Box<str> = ns.as_str().into();
+    let new_ns = Gc::new(mc, NixString::with_context(s, new_ctx));
+    m.return_from_primop(Value::new_gc(new_ns), reader)
+}
+
+pub fn get_context<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    if !val.is::<StringId>() && val.as_gc::<NixString>().is_none() {
+        return m.finish_type_err(NixType::String, val.ty());
+    }
+    let elems = ctx.get_string_context(val);
+
+    struct Info {
+        path: bool,
+        all_outputs: bool,
+        outputs: SmallVec<[Box<str>; 2]>,
+    }
+    impl Info {
+        fn new() -> Self {
+            Self {
+                path: false,
+                all_outputs: false,
+                outputs: SmallVec::new(),
+            }
+        }
+    }
+    let mut by_path: std::collections::BTreeMap<Box<str>, Info> = std::collections::BTreeMap::new();
+    for elem in elems {
+        match elem {
+            StringContextElem::Opaque { path } => {
+                by_path.entry(path.clone()).or_insert_with(Info::new).path = true;
+            }
+            StringContextElem::DrvDeep { drv_path } => {
+                by_path
+                    .entry(drv_path.clone())
+                    .or_insert_with(Info::new)
+                    .all_outputs = true;
+            }
+            StringContextElem::Built { drv_path, output } => {
+                by_path
+                    .entry(drv_path.clone())
+                    .or_insert_with(Info::new)
+                    .outputs
+                    .push(output.clone());
+            }
+        }
+    }
+
+    let mut outer_entries: SmallVec<[(StringId, Value<'gc>); 4]> = SmallVec::new();
+    for (path, mut info) in by_path {
+        info.outputs.sort();
+        info.outputs.dedup();
+
+        let mut sub: SmallVec<[(StringId, Value<'gc>); 4]> = SmallVec::new();
+        if info.all_outputs {
+            sub.push((ctx.intern_string("allOutputs"), Value::new_inline(true)));
+        }
+        if !info.outputs.is_empty() {
+            let items: smallvec::SmallVec<[Value<'gc>; 4]> = info
+                .outputs
+                .iter()
+                .map(|o| Value::new_inline(ctx.intern_string(o)))
+                .collect();
+            let list = VmList::new(mc, items);
+            sub.push((ctx.intern_string("outputs"), Value::new_gc(list)));
+        }
+        if info.path {
+            sub.push((ctx.intern_string("path"), Value::new_inline(true)));
+        }
+        sub.sort_by_key(|(k, _)| *k);
+        let sub_attrs = Gc::new(mc, AttrSet::from_sorted_unchecked(sub));
+
+        outer_entries.push((ctx.intern_string(&path), Value::new_gc(sub_attrs)));
+    }
+    outer_entries.sort_by_key(|(k, _)| *k);
+
+    let outer = Gc::new(mc, AttrSet::from_sorted_unchecked(outer_entries));
+    m.return_from_primop(Value::new_gc(outer), reader)
+}
+
+/// appendContext :: String -> AttrSet -> String
+/// The context AttrSet maps store-path strings to `{ path?: Bool, allOutputs?:
+/// Bool, outputs?: [String] }`. Each present field contributes one
+/// StringContextElem to the result.
+///
+/// Requires forcing nested attrset values and list elements lazily, so it's
+/// structured as a state machine with the following stack layout:
+///
+///   [strVal, attrs, idx, acc]                       - outer loop
+///   [strVal, attrs, idx, acc, entryAttrs]           - after entry forced
+///   [strVal, attrs, idx, acc, list]                 - after `outputs` forced
+///   [strVal, attrs, idx, acc, list, oidx]           - output-element loop
+///   [strVal, attrs, idx, acc, list, oidx, outElem]  - after element forced
+///
+/// `acc` is a sentinel `NixString` whose `data` is empty and whose `context`
+/// is the accumulator. The string value itself is preserved in `strVal` and
+/// retrieved at finalization.
+///
+// TODO: handle thunk-valued `path` and `allOutputs` sub-attrs; currently they
+// must be already-evaluated booleans.
+pub fn append_context<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let (str_val, attrs) = m.force_and_retry::<(StrictValue, Gc<AttrSet>)>(reader, mc)?;
+
+    let initial_ctx: StringContext = ctx.get_string_context(str_val).clone();
+    let acc = Gc::new(mc, NixString::with_context("", initial_ctx));
+
+    m.push(str_val.relax());
+    m.push(Value::new_gc(attrs));
+    m.push(Value::new_inline(0i32));
+    m.push(Value::new_gc(acc));
+
+    reader.set_pc(PrimOpPhase::AppendContextLoop.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn append_context_loop<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(1).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let attrs = m.peek_forced(2).as_gc::<AttrSet>().unwrap();
+
+    if idx as usize >= attrs.entries.len() {
+        return append_context_finalize(m, ctx, reader, mc);
+    }
+
+    let entry_val = attrs.entries[idx as usize].1;
+    m.push(entry_val);
+    m.force_slot_to_pc(
+        0,
+        reader,
+        mc,
+        PrimOpPhase::AppendContextEntryForced.ip() as usize,
+    )?;
+    reader.set_pc(PrimOpPhase::AppendContextEntryForced.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn append_context_entry_forced<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // Stack: [strVal, attrs, idx, acc, entryAttrs(thunk)]
+    // The slot still holds the Thunk pointer; re-force to extract the now-
+    // Evaluated value into the slot.
+    m.force_slot(0, reader, mc)?;
+    let entry_val = m.peek_forced(0);
+    let Some(entry_attrs) = entry_val.as_gc::<AttrSet>() else {
+        return m.finish_type_err(NixType::AttrSet, entry_val.ty());
+    };
+
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(2).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let outer = m.peek_forced(3).as_gc::<AttrSet>().unwrap();
+    let path_key = outer.entries[idx as usize].0;
+    let path_str_owned: Box<str> = ctx.resolve_string(path_key).into();
+    if !path_str_owned.starts_with("/nix/store/") {
+        return m.finish_err(Error::eval_error(format!(
+            "context key '{path_str_owned}' is not a store path"
+        )));
+    }
+
+    // Eagerly handle `path` and `allOutputs` (assumed already-forced
+    // booleans - most callers either set them to literal `true` or omit
+    // them entirely).
+    // TODO: force these two attributes correctly
+    let path_id = ctx.intern_string("path");
+    let all_outputs_id = ctx.intern_string("allOutputs");
+    let outputs_id = ctx.intern_string("outputs");
+
+    #[allow(clippy::unwrap_used)]
+    let acc_gc = m.peek(1).as_gc::<NixString>().unwrap();
+    let mut new_acc: StringContext = acc_gc.context().iter().cloned().collect();
+
+    if let Some(v) = entry_attrs.lookup(path_id)
+        && v.as_inline::<bool>() == Some(true)
+    {
+        new_acc.insert(StringContextElem::Opaque {
+            path: path_str_owned.clone(),
+        });
+    }
+
+    if let Some(v) = entry_attrs.lookup(all_outputs_id)
+        && v.as_inline::<bool>() == Some(true)
+    {
+        if !path_str_owned.ends_with(".drv") {
+            return m.finish_err(Error::eval_error(format!(
+                "tried to add all-outputs context of {path_str_owned}, which is not a derivation, to a string"
+            )));
+        }
+        new_acc.insert(StringContextElem::DrvDeep {
+            drv_path: path_str_owned.clone(),
+        });
+    }
+
+    let new_acc_gc = Gc::new(mc, NixString::with_context("", new_acc));
+    m.replace(1, Value::new_gc(new_acc_gc));
+
+    if let Some(outputs_val) = entry_attrs.lookup(outputs_id) {
+        m.replace(0, outputs_val);
+        m.force_slot_to_pc(
+            0,
+            reader,
+            mc,
+            PrimOpPhase::AppendContextOutputsForced.ip() as usize,
+        )?;
+        reader.set_pc(PrimOpPhase::AppendContextOutputsForced.ip() as usize);
+        return Step::Continue(());
+    }
+
+    let _ = m.pop();
+    #[allow(clippy::unwrap_used)]
+    let idx_back = m.peek(1).as_inline::<i32>().unwrap();
+    m.replace(1, Value::new_inline(idx_back + 1));
+    reader.set_pc(PrimOpPhase::AppendContextLoop.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn append_context_outputs_forced<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    _ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    m.force_slot(0, reader, mc)?;
+    let list_val = m.peek_forced(0);
+    let Some(list) = list_val.as_gc::<VmList>() else {
+        return m.finish_type_err(NixType::List, list_val.ty());
+    };
+    if list.inner.borrow().is_empty() {
+        // Stack: [strVal, attrs, idx, acc, list] -> drop list, bump idx.
+        let _ = m.pop();
+        #[allow(clippy::unwrap_used)]
+        let idx_back = m.peek(1).as_inline::<i32>().unwrap();
+        m.replace(1, Value::new_inline(idx_back + 1));
+        reader.set_pc(PrimOpPhase::AppendContextLoop.ip() as usize);
+        return Step::Continue(());
+    }
+
+    m.push(Value::new_inline(0i32));
+    reader.set_pc(PrimOpPhase::AppendContextOutputElementLoop.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn append_context_output_element_loop<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    _ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    #[allow(clippy::unwrap_used)]
+    let oidx = m.peek(0).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let list = m.peek_forced(1).as_gc::<VmList>().unwrap();
+    let len = list.inner.borrow().len();
+    if oidx as usize >= len {
+        // Stack: [strVal, attrs, idx, acc, list, oidx] -> drop oidx & list,
+        // bump idx in place.
+        let _ = m.pop();
+        let _ = m.pop();
+        #[allow(clippy::unwrap_used)]
+        let idx_back = m.peek(1).as_inline::<i32>().unwrap();
+        m.replace(1, Value::new_inline(idx_back + 1));
+        reader.set_pc(PrimOpPhase::AppendContextLoop.ip() as usize);
+        return Step::Continue(());
+    }
+
+    let elem = list.inner.borrow()[oidx as usize];
+    m.push(elem);
+    m.force_slot_to_pc(
+        0,
+        reader,
+        mc,
+        PrimOpPhase::AppendContextOutputElementForced.ip() as usize,
+    )?;
+    reader.set_pc(PrimOpPhase::AppendContextOutputElementForced.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn append_context_output_element_forced<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    m.force_slot(0, reader, mc)?;
+    let elem = m.peek_forced(0);
+    let Some(output_name) = ctx.get_string(elem) else {
+        return m.finish_type_err(NixType::String, elem.ty());
+    };
+    let output_name: Box<str> = output_name.into();
+
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(4).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let outer = m.peek_forced(5).as_gc::<AttrSet>().unwrap();
+    let path_key = outer.entries[idx as usize].0;
+    let path_str: Box<str> = ctx.resolve_string(path_key).into();
+    if !path_str.ends_with(".drv") {
+        return m.finish_err(Error::eval_error(format!(
+            "tried to add derivation output context of {path_str}, which is not a derivation, to a string"
+        )));
+    }
+
+    #[allow(clippy::unwrap_used)]
+    let acc_gc = m.peek(3).as_gc::<NixString>().unwrap();
+    let mut new_acc: StringContext = acc_gc.context().iter().cloned().collect();
+    new_acc.insert(StringContextElem::Built {
+        drv_path: path_str,
+        output: output_name,
+    });
+    let new_acc_gc = Gc::new(mc, NixString::with_context("", new_acc));
+    m.replace(3, Value::new_gc(new_acc_gc));
+
+    // Stack: [strVal, attrs, idx, acc, list, oidx, outElem] -> drop outElem,
+    // bump oidx in place.
+    let _ = m.pop();
+    #[allow(clippy::unwrap_used)]
+    let oidx = m.peek(0).as_inline::<i32>().unwrap();
+    m.replace(0, Value::new_inline(oidx + 1));
+    reader.set_pc(PrimOpPhase::AppendContextOutputElementLoop.ip() as usize);
+    Step::Continue(())
+}
+
+fn append_context_finalize<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // Stack: [strVal, attrs, idx, acc]
+    #[allow(clippy::unwrap_used)]
+    let acc_gc = m.pop().as_gc::<NixString>().unwrap();
+    let _ = m.pop(); // idx
+    let _ = m.pop(); // attrs
+    let str_val_raw = m.pop();
+
+    // The strVal was already forced at entry; restrict() is infallible here.
+    let str_val = str_val_raw
+        .restrict()
+        .unwrap_or_else(|_| panic!("appendContext: strVal unexpectedly a thunk"));
+
+    let s_str = ctx.get_string(str_val).unwrap_or("").to_owned();
+    let context: StringContext = acc_gc.context().iter().cloned().collect();
+    let result = if context.is_empty() {
+        let sid = ctx.intern_string(s_str);
+        Value::new_inline(sid)
+    } else {
+        let ns = Gc::new(mc, NixString::with_context(s_str, context));
+        Value::new_gc(ns)
+    };
+    m.return_from_primop(result, reader)
+}

fix-vm/src/primops/control.rs

@@ -0,0 +1,362 @@
+use fix_bytecode::PrimOpPhase;
+use fix_error::Error;
+use fix_runtime::{
+    AttrSet, BytecodeReader, Closure, Env, List, Machine, MachineExt, Step, StrictValue, Value,
+    VmRuntimeCtx, VmRuntimeCtxExt,
+};
+use gc_arena::{Gc, Mutation, RefLock};
+use smallvec::SmallVec;
+
+pub fn seq<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // stack: [e1, e2] - force e1, return e2
+    m.force_slot(1, reader, mc)?;
+    let e2 = m.pop();
+    let _ = m.pop();
+    m.return_from_primop(e2, reader)
+}
+
+pub fn abort<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // stack: [msg] - force msg, then abort with it
+    m.force_slot(0, reader, mc)?;
+    let msg_val = m.peek_forced(0);
+    let msg = ctx.get_string(msg_val).unwrap_or("<non-string-value>");
+    m.finish_err(Error::eval_error(format!(
+        "evaluation aborted with the following error message: '{msg}'"
+    )))
+}
+
+pub fn deep_seq_force_top<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // stack: [e1, e2] - force e1, return e2
+    m.force_slot(1, reader, mc)?;
+
+    let e1 = m.peek_forced(1);
+
+    let children: SmallVec<_> = if let Some(attrs) = e1.as_gc::<AttrSet>() {
+        let attrs = &attrs.entries;
+        if attrs.is_empty() {
+            SmallVec::new()
+        } else {
+            attrs.iter().map(|&(_, v)| v).collect()
+        }
+    } else if let Some(list) = e1.as_gc::<List<'gc>>() {
+        let inner = list.inner.borrow();
+        if inner.is_empty() {
+            SmallVec::new()
+        } else {
+            inner.iter().copied().collect()
+        }
+    } else {
+        SmallVec::new()
+    };
+
+    if children.is_empty() {
+        let e2 = m.pop();
+        let _ = m.pop();
+        return m.return_from_primop(e2, reader);
+    }
+
+    let count = children.len() as i32;
+    let seen: Gc<'gc, List<'gc>> = Gc::new(mc, List::default());
+    let worklist: Gc<'gc, List<'gc>> = List::new(mc, children);
+
+    let e2 = m.pop();
+    let _ = m.pop();
+    m.push(e2);
+    m.push(Value::new_gc(seen));
+    m.push(Value::new_gc(worklist));
+    m.push(Value::new_inline(count));
+    reader.set_pc(PrimOpPhase::DeepSeqPush.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn deep_seq_push<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // stack: [e2, seen, worklist, counter]
+    #[allow(clippy::unwrap_used)]
+    let counter = m.peek(0).as_inline::<i32>().unwrap();
+    if counter == 0 {
+        let _ = m.pop(); // counter
+        let _ = m.pop(); // worklist
+        let _ = m.pop(); // seen
+        let val = m.pop();
+        return m.return_from_primop(val, reader);
+    }
+
+    #[allow(clippy::unwrap_used)]
+    let worklist = m.peek_forced(1).as_gc::<List<'gc>>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let item = worklist.unlock(mc).borrow_mut().pop().unwrap();
+    m.replace(0, Value::new_inline(counter - 1));
+    m.push(item);
+
+    // force item at TOS, resume at DeepSeqLoop after force
+    m.force_slot_to_pc(0, reader, mc, PrimOpPhase::DeepSeqLoop.ip() as usize)?;
+    reader.set_pc(PrimOpPhase::DeepSeqLoop.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn deep_seq_loop<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // stack after pop: [e2, seen, worklist, counter]
+    let item = m.pop();
+    #[allow(clippy::unwrap_used)]
+    let counter = m.peek(0).as_inline::<i32>().unwrap();
+
+    let mut added: usize = 0;
+    if let Some(attrs) = item.as_gc::<AttrSet>() {
+        let attrs = &attrs.entries;
+        #[allow(clippy::unwrap_used)]
+        let seen = m.peek_forced(2).as_gc::<List<'gc>>().unwrap();
+        if !is_value_in_seen(seen, item) {
+            add_value_to_seen(seen, mc, item);
+            #[allow(clippy::unwrap_used)]
+            let worklist = m.peek_forced(1).as_gc::<List<'gc>>().unwrap();
+            {
+                let mut wl = worklist.unlock(mc).borrow_mut();
+                for &(_, v) in attrs.iter() {
+                    wl.push(v);
+                }
+                added = attrs.len();
+            }
+        }
+    } else if let Some(list) = item.as_gc::<List<'gc>>() {
+        #[allow(clippy::unwrap_used)]
+        let seen = m.peek_forced(2).as_gc::<List<'gc>>().unwrap();
+        if !is_value_in_seen(seen, item) {
+            add_value_to_seen(seen, mc, item);
+            #[allow(clippy::unwrap_used)]
+            let worklist = m.peek_forced(1).as_gc::<List<'gc>>().unwrap();
+            {
+                let inner = list.inner.borrow();
+                let mut wl = worklist.unlock(mc).borrow_mut();
+                for &v in inner.iter() {
+                    wl.push(v);
+                }
+                added = inner.len();
+            }
+        }
+    }
+
+    m.replace(0, Value::new_inline(counter + added as i32));
+    reader.set_pc(PrimOpPhase::DeepSeqPush.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn force_result_shallow<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    m.force_slot(0, reader, mc)?;
+    let val = m.peek_forced(0);
+
+    let (count, has_children) = if let Some(attrs) = val.as_gc::<AttrSet>() {
+        let len = attrs.entries.len();
+        (len, len > 0)
+    } else if let Some(list) = val.as_gc::<List<'gc>>() {
+        let len = list.inner.borrow().len();
+        (len, len > 0)
+    } else {
+        (0, false)
+    };
+
+    if !has_children {
+        let val = m.pop();
+        return m.finish_ok(ctx.convert_value(val));
+    }
+
+    m.push(Value::new_inline(0i32));
+    m.push(Value::new_inline(count as i32));
+    reader.set_pc(PrimOpPhase::ForceResultShallowPush.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn force_result_shallow_push<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(1).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let len = m.peek(0).as_inline::<i32>().unwrap();
+
+    if idx == len {
+        let _ = m.pop(); // len
+        let _ = m.pop(); // idx
+        let val = m.pop();
+        return m.finish_ok(ctx.convert_value(val));
+    }
+
+    let val = m.peek_forced(2);
+    let child = if let Some(attrs) = val.as_gc::<AttrSet>() {
+        attrs.entries.get(idx as usize).map(|&(_, v)| v)
+    } else if let Some(list) = val.as_gc::<List<'gc>>() {
+        list.inner.borrow().get(idx as usize).copied()
+    } else {
+        None
+    };
+
+    if let Some(child) = child {
+        m.replace(1, Value::new_inline(idx + 1));
+        m.push(child);
+        m.force_slot_to_pc(
+            0,
+            reader,
+            mc,
+            PrimOpPhase::ForceResultShallowLoop.ip() as usize,
+        )?;
+        reader.set_pc(PrimOpPhase::ForceResultShallowLoop.ip() as usize);
+    }
+    Step::Continue(())
+}
+
+pub fn force_result_shallow_loop<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    _mc: &Mutation<'gc>,
+) -> Step {
+    let _ = m.pop(); // forced child
+    reader.set_pc(PrimOpPhase::ForceResultShallowPush.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn force_result_deep_finish<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    m.finish_ok(ctx.convert_value(val.relax()))
+}
+
+fn is_value_in_seen<'gc>(seen: Gc<'gc, List<'gc>>, val: Value<'gc>) -> bool {
+    if !is_container(val) {
+        return false;
+    }
+    let target = val.to_bits();
+    for &v in seen.inner.borrow().iter() {
+        if v.to_bits() == target {
+            return true;
+        }
+    }
+    false
+}
+
+fn add_value_to_seen<'gc>(seen: Gc<'gc, List<'gc>>, mc: &Mutation<'gc>, val: Value<'gc>) {
+    if is_container(val) {
+        seen.unlock(mc).borrow_mut().push(val);
+    }
+}
+
+pub fn call_functor_1<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // Stack invariant on every (re-)entry: [..., orig_arg, self, functor]
+    // where `functor` is TOS. Retries during force land back here safely.
+    let functor = m.force_and_retry::<StrictValue>(reader, mc)?;
+    // Stack now: [..., orig_arg, self]
+    let self_val = m.pop();
+    m.push(functor.relax());
+    // Stack: [..., orig_arg, functor]
+    // Call 1: functor(self). Resume into CallFunctor2 once it returns.
+    m.call(
+        reader,
+        mc,
+        self_val,
+        PrimOpPhase::CallFunctor2.ip() as usize,
+    )
+}
+
+pub fn call_functor_2<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // Stack on entry: [..., orig_arg, intermediate]
+    // call_stack top: synthetic frame with caller's resume_pc.
+    let intermediate = m.pop();
+    let orig_arg = m.pop();
+    let saved = m.pop_call_frame().expect("functor outer frame missing");
+    m.set_env(saved.env);
+    m.push(intermediate);
+    // Call 2: intermediate(orig_arg). Resume to caller.
+    m.call(reader, mc, orig_arg, saved.pc)
+}
+
+pub fn call_pattern<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let (func, attrset) = m.force_and_retry::<(Gc<Closure>, Gc<AttrSet>)>(reader, mc)?;
+
+    let Closure {
+        ip,
+        n_locals,
+        env,
+        pattern,
+    } = *func;
+    let Some(pattern) = pattern else {
+        unreachable!()
+    };
+    // TODO: get function name
+    // TODO: param spans
+    if !pattern.ellipsis {
+        for key in pattern.required.iter().copied() {
+            if attrset.lookup(key).is_none() {
+                let name = ctx.resolve_string(key);
+                return m.finish_err(Error::eval_error(format!(
+                    "function 'anonymous lambda' called without required argument '{name}'"
+                )));
+            }
+        }
+        for &(key, _) in attrset.entries.iter() {
+            let is_expected = pattern.required.contains(&key) || pattern.optional.contains(&key);
+            if !is_expected {
+                let name = ctx.resolve_string(key);
+                return m.finish_err(Error::eval_error(format!(
+                    "function 'anonymous lambda' called with unexpected argument '{name}'"
+                )));
+            }
+        }
+    }
+
+    let new_env = Gc::new(
+        mc,
+        RefLock::new(Env::with_arg(Value::new_gc(attrset), n_locals, env)),
+    );
+    reader.set_pc(ip as usize);
+    m.set_env(new_env);
+
+    Step::Continue(())
+}
+
+fn is_container(val: Value<'_>) -> bool {
+    val.is::<AttrSet>() || val.is::<List<'_>>()
+}

fix-vm/src/primops/conv.rs

@@ -0,0 +1,51 @@
+use fix_error::Error;
+use fix_lang::StringId;
+use fix_runtime::{
+    BytecodeReader, Machine, MachineExt, NixString, NixType, Path, Step, StrictValue, Value,
+    VmRuntimeCtx,
+};
+use gc_arena::Mutation;
+
+pub fn to_string<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    _ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    if val.is::<StringId>() || val.is::<NixString>() {
+        return m.return_from_primop(val.relax(), reader);
+    }
+    if let Some(p) = val.as_inline::<Path>() {
+        return m.return_from_primop(Value::new_inline(p.0), reader);
+    }
+    //  TODO: derivations / `__toString` / `outPath`,
+    //        numbers, lists.
+    m.finish_err(Error::eval_error(format!(
+        "cannot coerce {} to a string",
+        val.ty()
+    )))
+}
+
+pub fn type_of<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    let name: &str = match val.ty() {
+        NixType::Int => "int",
+        NixType::Float => "float",
+        NixType::Bool => "bool",
+        NixType::Null => "null",
+        NixType::String => "string",
+        NixType::Path => "path",
+        NixType::AttrSet => "set",
+        NixType::List => "list",
+        NixType::Closure | NixType::PrimOp | NixType::PrimOpApp => "lambda",
+        NixType::Thunk => unreachable!("forced"),
+    };
+    let sid = ctx.intern_string(name);
+    m.return_from_primop(Value::new_inline(sid), reader)
+}

fix-vm/src/primops/eq.rs

@@ -0,0 +1,237 @@
+use fix_bytecode::PrimOpPhase;
+use fix_runtime::{
+    AttrSet, BytecodeReader, CallFrame, List, Machine, MachineExt, NixNum, Null, Path, Step,
+    StrictValue, Value, VmRuntimeCtx, VmRuntimeCtxExt,
+};
+use gc_arena::{Gc, Mutation};
+use smallvec::SmallVec;
+
+pub fn start_eq<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+    lhs: StrictValue<'gc>,
+    rhs: StrictValue<'gc>,
+    negate: bool,
+) -> Step {
+    match shallow_eq(ctx, lhs, rhs) {
+        ShallowEq::True => {
+            m.push(Value::new_inline(!negate));
+            Step::Continue(())
+        }
+        ShallowEq::False => {
+            m.push(Value::new_inline(negate));
+            Step::Continue(())
+        }
+        ShallowEq::RecurseList(la, lb) => {
+            let lhs_init: SmallVec<[Value<'gc>; 4]> = la.inner.borrow().iter().copied().collect();
+            let rhs_init: SmallVec<[Value<'gc>; 4]> = lb.inner.borrow().iter().copied().collect();
+            enter_eq_machine(m, reader, mc, negate, lhs_init, rhs_init)
+        }
+        ShallowEq::RecurseAttrs(a, b) => {
+            let lhs_init: SmallVec<[Value<'gc>; 4]> = a.entries.iter().map(|&(_, v)| v).collect();
+            let rhs_init: SmallVec<[Value<'gc>; 4]> = b.entries.iter().map(|&(_, v)| v).collect();
+            enter_eq_machine(m, reader, mc, negate, lhs_init, rhs_init)
+        }
+    }
+}
+
+pub fn eq_step<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let rhs_q = m
+        .peek(0)
+        .as_gc::<List<'gc>>()
+        .expect("eq state corrupted: rhs_queue");
+    let lhs_q = m
+        .peek(1)
+        .as_gc::<List<'gc>>()
+        .expect("eq state corrupted: lhs_queue");
+    let result = m
+        .peek(2)
+        .as_inline::<bool>()
+        .expect("eq state corrupted: result");
+
+    if !result || lhs_q.inner.borrow().is_empty() {
+        return finalize(m, reader);
+    }
+
+    let lhs = lhs_q
+        .unlock(mc)
+        .borrow_mut()
+        .pop()
+        .expect("non-empty lhs queue");
+    let rhs = rhs_q
+        .unlock(mc)
+        .borrow_mut()
+        .pop()
+        .expect("non-empty rhs queue");
+    m.push(lhs);
+    m.push(rhs);
+    reader.set_pc(PrimOpPhase::EqForce.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn eq_force<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let (lhs, rhs) = m.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+    apply_pair(m, ctx, mc, lhs, rhs);
+    reader.set_pc(PrimOpPhase::EqStep.ip() as usize);
+    Step::Continue(())
+}
+
+fn finalize<'gc, M: Machine<'gc>>(m: &mut M, reader: &mut BytecodeReader<'_>) -> Step {
+    let _ = m.pop();
+    let _ = m.pop();
+    let result = m
+        .pop()
+        .as_inline::<bool>()
+        .expect("eq state corrupted: result");
+    let negate = m
+        .pop()
+        .as_inline::<bool>()
+        .expect("eq state corrupted: negate");
+    m.return_from_primop(Value::new_inline(result ^ negate), reader)
+}
+
+fn apply_pair<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &impl VmRuntimeCtx,
+    mc: &Mutation<'gc>,
+    lhs: StrictValue<'gc>,
+    rhs: StrictValue<'gc>,
+) {
+    match shallow_eq(ctx, lhs, rhs) {
+        ShallowEq::True => {}
+        ShallowEq::False => {
+            m.replace(2, Value::new_inline(false));
+        }
+        ShallowEq::RecurseList(la, lb) => {
+            extend_queues(
+                m,
+                mc,
+                la.inner.borrow().iter().copied(),
+                lb.inner.borrow().iter().copied(),
+            );
+        }
+        ShallowEq::RecurseAttrs(a, b) => {
+            extend_queues(
+                m,
+                mc,
+                a.entries.iter().map(|&(_, v)| v),
+                b.entries.iter().map(|&(_, v)| v),
+            );
+        }
+    }
+}
+
+fn extend_queues<'gc, M, L, R>(m: &mut M, mc: &Mutation<'gc>, lhs_iter: L, rhs_iter: R)
+where
+    M: Machine<'gc>,
+    L: IntoIterator<Item = Value<'gc>>,
+    R: IntoIterator<Item = Value<'gc>>,
+{
+    let rhs_q = m
+        .peek(0)
+        .as_gc::<List<'gc>>()
+        .expect("eq state corrupted: rhs_queue");
+    let lhs_q = m
+        .peek(1)
+        .as_gc::<List<'gc>>()
+        .expect("eq state corrupted: lhs_queue");
+    let mut lq = lhs_q.unlock(mc).borrow_mut();
+    let mut rq = rhs_q.unlock(mc).borrow_mut();
+    for (x, y) in lhs_iter.into_iter().zip(rhs_iter) {
+        lq.push(x);
+        rq.push(y);
+    }
+}
+
+fn enter_eq_machine<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+    negate: bool,
+    lhs_init: SmallVec<[Value<'gc>; 4]>,
+    rhs_init: SmallVec<[Value<'gc>; 4]>,
+) -> Step {
+    let resume_pc = reader.pc();
+    m.push_call_frame(CallFrame {
+        pc: resume_pc,
+        thunk: None,
+        env: m.env(),
+    });
+    m.inc_call_depth();
+    m.push(Value::new_inline(negate));
+    m.push(Value::new_inline(true));
+    m.push(Value::new_gc(List::new(mc, lhs_init)));
+    m.push(Value::new_gc(List::new(mc, rhs_init)));
+    reader.set_pc(PrimOpPhase::EqStep.ip() as usize);
+    Step::Continue(())
+}
+
+enum ShallowEq<'gc> {
+    True,
+    False,
+    RecurseList(Gc<'gc, List<'gc>>, Gc<'gc, List<'gc>>),
+    RecurseAttrs(Gc<'gc, AttrSet<'gc>>, Gc<'gc, AttrSet<'gc>>),
+}
+
+fn shallow_eq<'gc>(
+    ctx: &impl VmRuntimeCtx,
+    lhs: StrictValue<'gc>,
+    rhs: StrictValue<'gc>,
+) -> ShallowEq<'gc> {
+    if let (Some(a), Some(b)) = (lhs.as_num(), rhs.as_num()) {
+        let eq = match (a, b) {
+            (NixNum::Int(a), NixNum::Int(b)) => a == b,
+            (NixNum::Float(a), NixNum::Float(b)) => a == b,
+            (NixNum::Int(a), NixNum::Float(b)) => a as f64 == b,
+            (NixNum::Float(a), NixNum::Int(b)) => a == b as f64,
+        };
+        return bool_outcome(eq);
+    }
+    if let (Some(a), Some(b)) = (lhs.as_inline::<bool>(), rhs.as_inline::<bool>()) {
+        return bool_outcome(a == b);
+    }
+    if lhs.is::<Null>() && rhs.is::<Null>() {
+        return ShallowEq::True;
+    }
+    if let (Some(a), Some(b)) = (lhs.as_inline::<Path>(), rhs.as_inline::<Path>()) {
+        return bool_outcome(a.0 == b.0);
+    }
+    if let (Some(a), Some(b)) = (ctx.get_string(lhs), ctx.get_string(rhs)) {
+        return bool_outcome(a == b);
+    }
+    if let (Some(a), Some(b)) = (lhs.as_gc::<List<'gc>>(), rhs.as_gc::<List<'gc>>()) {
+        if a.inner.borrow().len() != b.inner.borrow().len() {
+            return ShallowEq::False;
+        }
+        return ShallowEq::RecurseList(a, b);
+    }
+    if let (Some(a), Some(b)) = (lhs.as_gc::<AttrSet<'gc>>(), rhs.as_gc::<AttrSet<'gc>>()) {
+        let ae = &a.entries;
+        let be = &b.entries;
+        if ae.len() != be.len() {
+            return ShallowEq::False;
+        }
+        for (l, r) in ae.iter().zip(be.iter()) {
+            if l.0 != r.0 {
+                return ShallowEq::False;
+            }
+        }
+        return ShallowEq::RecurseAttrs(a, b);
+    }
+    ShallowEq::False
+}
+
+fn bool_outcome<'gc>(b: bool) -> ShallowEq<'gc> {
+    if b { ShallowEq::True } else { ShallowEq::False }
+}

fix-vm/src/primops/io.rs

@@ -0,0 +1,190 @@
+use std::path::PathBuf;
+
+use fix_bytecode::PrimOpPhase;
+use fix_error::Error;
+use fix_lang::StringId;
+use fix_runtime::{
+    AttrSet, Break, BytecodeReader, CallFrame, Machine, MachineExt, Path, PendingLoad,
+    PendingScope, Step, StrictValue, Value, VmRuntimeCtx, VmRuntimeCtxExt, canon_path_str,
+};
+use gc_arena::{Gc, Mutation};
+use hashbrown::HashSet;
+
+pub fn import<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // stack: [path]
+    let path_val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    let path_str = match ctx.get_string_or_path(path_val) {
+        Some(s) => s.to_owned(),
+        None => {
+            return m.finish_err(Error::eval_error(format!(
+                "expected a path or string, got {}",
+                path_val.ty()
+            )));
+        }
+    };
+    let abs = match resolve_import_target(&path_str) {
+        Ok(p) => p,
+        Err(e) => return m.finish_err(e),
+    };
+
+    if let Some(cached) = m.import_cache_get(&abs) {
+        return m.return_from_primop(cached, reader);
+    }
+
+    // Stash the resolved path on the stack as a string-id so the
+    // finalizer can use it as the cache key. The slot we pop here was
+    // freed by `force_and_retry`, so we simply push.
+    let path_sid = ctx.intern_string(abs.to_string_lossy());
+    m.push(Value::new_inline(path_sid));
+    let env = m.env();
+    m.push_call_frame(CallFrame {
+        pc: PrimOpPhase::ImportFinalize.ip() as usize,
+        thunk: None,
+        env,
+    });
+
+    m.set_pending_load(PendingLoad {
+        path: abs,
+        scope: None,
+    });
+    Step::Break(Break::LoadFile)
+}
+
+pub fn import_finalize<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+) -> Step {
+    // stack: [path_sid, return_value]
+    let val = m.pop();
+    #[allow(clippy::unwrap_used)]
+    let path_sid = m.pop().as_inline::<StringId>().unwrap();
+    // The cache key is keyed by the absolute path string we interned in
+    // `import`. Resolve it back to the host PathBuf.
+    let path_str = ctx.resolve_string(path_sid).to_owned();
+    m.import_cache_insert(PathBuf::from(path_str), val);
+    m.push(val);
+    let Some(CallFrame {
+        pc: ret_pc,
+        thunk: _,
+        env,
+    }) = m.pop_call_frame()
+    else {
+        unreachable!()
+    };
+    reader.set_pc(ret_pc);
+    // FIXME:
+    // m.dec_call_depth();
+    m.set_env(env);
+    Step::Continue(())
+}
+
+pub fn scoped_import<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // stack: [scope, path]
+    let (scope_attrs, path_val) = m.force_and_retry::<(Gc<AttrSet>, StrictValue)>(reader, mc)?;
+    let path_str = match ctx.get_string_or_path(path_val) {
+        Some(s) => s.to_owned(),
+        None => {
+            return m.finish_err(Error::eval_error(format!(
+                "expected a path or string, got {}",
+                path_val.ty()
+            )));
+        }
+    };
+    let abs = match resolve_import_target(&path_str) {
+        Ok(p) => p,
+        Err(e) => return m.finish_err(e),
+    };
+
+    let keys: HashSet<StringId> = scope_attrs.entries.iter().map(|&(k, _)| k).collect();
+    let slot_id = m.scope_slots_push(Value::new_gc(scope_attrs));
+
+    let env = m.env();
+    m.push_call_frame(CallFrame {
+        pc: PrimOpPhase::ScopedImportFinalize.ip() as usize,
+        thunk: None,
+        env,
+    });
+
+    m.set_pending_load(PendingLoad {
+        path: abs,
+        scope: Some(PendingScope { keys, slot_id }),
+    });
+    Step::Break(Break::LoadFile)
+}
+
+pub fn scoped_import_finalize<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    _ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    _mc: &Mutation<'gc>,
+) -> Step {
+    // stack: [return_value]
+    // We intentionally do NOT pop the slot from `scope_slots` so that
+    // closures or thunks created inside the imported file can still
+    // resolve their scope after `scopedImport` returns.
+    let val = m.pop();
+    m.return_from_primop(val, reader)
+}
+
+pub fn path_exists<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let path_val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    // pathExists requires an absolute path. A `Path` value is
+    // always absolute; a string is accepted only if it starts with `/`.
+    let (path, is_path_value) = if let Some(p) = path_val.as_inline::<Path>() {
+        (ctx.resolve_string(p.0).to_owned(), true)
+    } else if let Some(s) = ctx.get_string(path_val) {
+        (s.to_owned(), false)
+    } else {
+        return m.finish_err(Error::eval_error(format!(
+            "expected a path or string, got {}",
+            path_val.ty()
+        )));
+    };
+    if !is_path_value && !path.starts_with('/') {
+        return m.finish_err(Error::eval_error(format!(
+            "string '{path}' doesn't represent an absolute path"
+        )));
+    }
+    // CppNix collapses consecutive slashes and resolves `.` / `..` lexically
+    // before checking. Trailing-slash / trailing-dot mean "must be a directory".
+    let must_be_dir = path.ends_with('/') || path.ends_with("/.");
+    let canon = canon_path_str(&path);
+    let p = std::path::Path::new(&canon);
+    let exists = if must_be_dir {
+        std::fs::metadata(p).map(|m| m.is_dir()).unwrap_or(false)
+    } else {
+        std::fs::symlink_metadata(p).is_ok()
+    };
+    m.return_from_primop(Value::new_inline(exists), reader)
+}
+
+/// Convert the user-supplied path string into an absolute, dotted-segment
+/// resolved `PathBuf` and append `default.nix` if the target is a directory.
+fn resolve_import_target(path: &str) -> Result<PathBuf, Box<Error>> {
+    let mut abs = PathBuf::from(path);
+    if !abs.is_absolute() {
+        return Err(Error::eval_error(format!(
+            "import: expected an absolute path, got '{path}'"
+        )));
+    }
+    if abs.is_dir() {
+        abs.push("default.nix");
+    }
+    Ok(abs)
+}

fix-vm/src/primops/list.rs

@@ -0,0 +1,283 @@
+use fix_bytecode::PrimOpPhase;
+use fix_runtime::{BytecodeReader, List, Machine, MachineExt, NixType, Step, StrictValue, Value};
+use gc_arena::Mutation;
+
+pub fn filter_force_list<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    m.force_slot(0, reader, mc)?;
+    let list = match m.peek_forced(0).expect_gc::<List>() {
+        Ok(list) => list,
+        Err(got) => return m.finish_type_err(NixType::List, got),
+    };
+    if list.inner.borrow().is_empty() {
+        let val = m.pop();
+        let _pred = m.pop();
+        return m.return_from_primop(val, reader);
+    }
+    // prepare stack layout: [ pred list idx acc ]
+    m.push(Value::new_inline(0));
+    m.push(Value::new_gc(List::new_gc(mc)));
+    reader.set_pc(PrimOpPhase::FilterCallPred.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn filter_call_pred<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    m.force_slot(3, reader, mc)?;
+    let pred = m.peek_forced(3);
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(1).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let elem = m.peek_forced(2).as_gc::<List>().unwrap().inner.borrow()[idx as usize];
+    m.push(pred.relax());
+    m.call(reader, mc, elem, PrimOpPhase::FilterCheck.ip() as usize)
+}
+
+pub fn filter_check<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let ret = m.force_and_retry::<bool>(reader, mc)?;
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(1).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let list = m.peek_forced(2).as_gc::<List>().unwrap();
+    let list = list.inner.borrow();
+    #[allow(clippy::unwrap_used)]
+    let acc = m.peek_forced(0).as_gc::<List>().unwrap();
+    if ret {
+        let mut acc = acc.unlock(mc).borrow_mut();
+        acc.push(list[idx as usize]);
+    }
+    if idx as usize == list.len() - 1 {
+        let acc = m.pop();
+        let _ = m.pop(); // idx
+        let _ = m.pop(); // list
+        let _ = m.pop(); // pred
+        return m.return_from_primop(acc, reader);
+    }
+    m.replace(1, Value::new_inline(idx + 1));
+    reader.set_pc(PrimOpPhase::FilterCallPred.ip() as usize);
+    Step::Continue(())
+}
+
+// foldl' op nul list
+//
+// Stack layouts across phases:
+//   Entry:  [op, nul, list]
+//   Empty:  [op, nul]
+//   Call1:  [op, list, idx, acc]
+//   Call2:  [op, list, idx, acc, intermediate]
+//   Update: [op, list, idx, acc, result]
+pub fn foldl_strict_entry<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    m.force_slot(0, reader, mc)?;
+    let list_val = m.peek_forced(0);
+    let Some(list) = list_val.as_gc::<List>() else {
+        return m.finish_type_err(NixType::List, list_val.ty());
+    };
+    if list.inner.borrow().is_empty() {
+        let _ = m.pop(); // list
+        reader.set_pc(PrimOpPhase::FoldlStrictEmpty.ip() as usize);
+        return Step::Continue(());
+    }
+    let list_val = m.pop();
+    let nul_val = m.pop();
+    m.push(list_val);
+    m.push(Value::new_inline(0i32));
+    m.push(nul_val);
+    reader.set_pc(PrimOpPhase::FoldlStrictCall1.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn foldl_strict_empty<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let nul = m.force_and_retry::<StrictValue>(reader, mc)?;
+    let _ = m.pop(); // op
+    m.return_from_primop(nul.relax(), reader)
+}
+
+pub fn foldl_strict_call1<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    m.force_slot(3, reader, mc)?;
+    let op = m.peek_forced(3);
+    let acc = m.peek(0);
+    m.push(op.relax());
+    m.call(reader, mc, acc, PrimOpPhase::FoldlStrictCall2.ip() as usize)
+}
+
+pub fn foldl_strict_call2<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(2).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let list = m.peek_forced(3).as_gc::<List>().unwrap();
+    let elem = list.inner.borrow()[idx as usize];
+    m.call(
+        reader,
+        mc,
+        elem,
+        PrimOpPhase::FoldlStrictUpdate.ip() as usize,
+    )
+}
+
+pub fn foldl_strict_update<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    _mc: &Mutation<'gc>,
+) -> Step {
+    let result = m.pop();
+    m.replace(0, result);
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(1).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let list = m.peek_forced(2).as_gc::<List>().unwrap();
+    let len = list.inner.borrow().len();
+    if (idx as usize) + 1 == len {
+        let acc = m.pop();
+        let _ = m.pop(); // idx
+        let _ = m.pop(); // list
+        let _ = m.pop(); // op
+        return m.return_from_primop(acc, reader);
+    }
+    m.replace(1, Value::new_inline(idx + 1));
+    reader.set_pc(PrimOpPhase::FoldlStrictCall1.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn all_entry<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    m.force_slot(0, reader, mc)?;
+    let list = match m.peek_forced(0).expect_gc::<List>() {
+        Ok(list) => list,
+        Err(got) => return m.finish_type_err(NixType::List, got),
+    };
+    // FIXME: force callable
+    m.force_slot(1, reader, mc)?;
+    if list.inner.borrow().is_empty() {
+        let _list = m.pop();
+        let _pred = m.pop();
+        return m.return_from_primop(Value::new_inline(true), reader);
+    }
+    // prepare stack layout: [ pred list idx ]
+    m.push(Value::new_inline(0));
+    reader.set_pc(PrimOpPhase::AllCallPred.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn all_call_pred<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let pred = m.peek_forced(2);
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(0).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let elem = m.peek_forced(1).as_gc::<List>().unwrap().inner.borrow()[idx as usize];
+    m.push(pred.relax());
+    m.call(reader, mc, elem, PrimOpPhase::AllCheck.ip() as usize)
+}
+
+pub fn all_check<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let ret = m.force_and_retry::<bool>(reader, mc)?;
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(0).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let list = m.peek_forced(1).as_gc::<List>().unwrap();
+    let list = list.inner.borrow();
+    if idx as usize == list.len() - 1 || !ret {
+        let _ = m.pop(); // idx
+        let _ = m.pop(); // list
+        let _ = m.pop(); // pred
+        return m.return_from_primop(Value::new_inline(ret), reader);
+    }
+    m.replace(0, Value::new_inline(idx + 1));
+    reader.set_pc(PrimOpPhase::AllCallPred.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn any_entry<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    m.force_slot(0, reader, mc)?;
+    let list = match m.peek_forced(0).expect_gc::<List>() {
+        Ok(list) => list,
+        Err(got) => return m.finish_type_err(NixType::List, got),
+    };
+    // FIXME: force callable
+    m.force_slot(1, reader, mc)?;
+    if list.inner.borrow().is_empty() {
+        let _list = m.pop();
+        let _pred = m.pop();
+        return m.return_from_primop(Value::new_inline(false), reader);
+    }
+    // prepare stack layout: [ pred list idx ]
+    m.push(Value::new_inline(0));
+    reader.set_pc(PrimOpPhase::AnyCallPred.ip() as usize);
+    Step::Continue(())
+}
+
+pub fn any_call_pred<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let pred = m.peek_forced(2);
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(0).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let elem = m.peek_forced(1).as_gc::<List>().unwrap().inner.borrow()[idx as usize];
+    m.push(pred.relax());
+    m.call(reader, mc, elem, PrimOpPhase::AnyCheck.ip() as usize)
+}
+
+pub fn any_check<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let ret = m.force_and_retry::<bool>(reader, mc)?;
+    #[allow(clippy::unwrap_used)]
+    let idx = m.peek(0).as_inline::<i32>().unwrap();
+    #[allow(clippy::unwrap_used)]
+    let list = m.peek_forced(1).as_gc::<List>().unwrap();
+    let list = list.inner.borrow();
+    if idx as usize == list.len() - 1 || ret {
+        let _ = m.pop(); // idx
+        let _ = m.pop(); // list
+        let _ = m.pop(); // pred
+        return m.return_from_primop(Value::new_inline(ret), reader);
+    }
+    m.replace(0, Value::new_inline(idx + 1));
+    reader.set_pc(PrimOpPhase::AnyCallPred.ip() as usize);
+    Step::Continue(())
+}

fix-vm/src/primops/mod.rs

@@ -0,0 +1,97 @@
+mod context;
+mod control;
+mod conv;
+mod eq;
+mod io;
+mod list;
+mod path;
+
+pub use context::*;
+pub use control::*;
+pub use conv::*;
+pub use eq::*;
+use fix_bytecode::PrimOpPhase;
+use fix_error::Error;
+use fix_runtime::{BytecodeReader, Machine, Step, VmRuntimeCtx};
+use gc_arena::Mutation;
+pub use io::*;
+pub use list::*;
+pub use path::*;
+
+#[allow(clippy::too_many_lines)]
+pub fn dispatch_primop<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    use PrimOpPhase::*;
+    let phase_disc = reader.read_u8();
+    let Ok(phase) = PrimOpPhase::try_from(phase_disc) else {
+        return m.finish_err(Error::eval_error("invalid primop phase"));
+    };
+    match phase {
+        Abort => abort(m, ctx, reader, mc),
+
+        All => all_entry(m, reader, mc),
+        AllCallPred => all_call_pred(m, reader, mc),
+        AllCheck => all_check(m, reader, mc),
+
+        Any => any_entry(m, reader, mc),
+        AnyCallPred => any_call_pred(m, reader, mc),
+        AnyCheck => any_check(m, reader, mc),
+
+        DeepSeq => deep_seq_force_top(m, reader, mc),
+        DeepSeqPush => deep_seq_push(m, reader, mc),
+        DeepSeqLoop => deep_seq_loop(m, reader, mc),
+        Seq => seq(m, reader, mc),
+
+        FilterForceList => filter_force_list(m, reader, mc),
+        FilterCallPred => filter_call_pred(m, reader, mc),
+        FilterCheck => filter_check(m, reader, mc),
+
+        FoldlStrict => foldl_strict_entry(m, reader, mc),
+        FoldlStrictEmpty => foldl_strict_empty(m, reader, mc),
+        FoldlStrictCall1 => foldl_strict_call1(m, reader, mc),
+        FoldlStrictCall2 => foldl_strict_call2(m, reader, mc),
+        FoldlStrictUpdate => foldl_strict_update(m, reader, mc),
+
+        ForceResultShallow => force_result_shallow(m, ctx, reader, mc),
+        ForceResultShallowPush => force_result_shallow_push(m, ctx, reader, mc),
+        ForceResultShallowLoop => force_result_shallow_loop(m, reader, mc),
+        ForceResultDeepFinish => force_result_deep_finish(m, ctx, reader, mc),
+
+        EqStep => eq_step(m, reader, mc),
+        EqForce => eq_force(m, ctx, reader, mc),
+
+        CallPattern => call_pattern(m, ctx, reader, mc),
+        CallFunctor1 => call_functor_1(m, reader, mc),
+        CallFunctor2 => call_functor_2(m, reader, mc),
+
+        Import => import(m, ctx, reader, mc),
+        ImportFinalize => import_finalize(m, ctx, reader),
+        ScopedImport => scoped_import(m, ctx, reader, mc),
+        ScopedImportFinalize => scoped_import_finalize(m, ctx, reader, mc),
+
+        PathExists => path_exists(m, ctx, reader, mc),
+        ToPath => to_path(m, ctx, reader, mc),
+        IsPath => is_path(m, reader, mc),
+        ToString => to_string(m, ctx, reader, mc),
+        TypeOf => type_of(m, ctx, reader, mc),
+
+        HasContext => has_context(m, ctx, reader, mc),
+        GetContext => get_context(m, ctx, reader, mc),
+        AppendContext => append_context(m, ctx, reader, mc),
+        AppendContextLoop => append_context_loop(m, ctx, reader, mc),
+        AppendContextEntryForced => append_context_entry_forced(m, ctx, reader, mc),
+        AppendContextOutputsForced => append_context_outputs_forced(m, ctx, reader, mc),
+        AppendContextOutputElementLoop => append_context_output_element_loop(m, ctx, reader, mc),
+        AppendContextOutputElementForced => {
+            append_context_output_element_forced(m, ctx, reader, mc)
+        }
+        UnsafeDiscardStringContext => unsafe_discard_string_context(m, ctx, reader, mc),
+        UnsafeDiscardOutputDependency => unsafe_discard_output_dependency(m, ctx, reader, mc),
+
+        phase => todo!("primop phase {phase:?}"),
+    }
+}

fix-vm/src/primops/path.rs

@@ -0,0 +1,43 @@
+use fix_error::Error;
+use fix_runtime::{
+    BytecodeReader, Machine, MachineExt, Path, Step, StrictValue, Value, VmRuntimeCtx,
+    VmRuntimeCtxExt, canon_path_str,
+};
+use gc_arena::Mutation;
+
+pub fn to_path<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    ctx: &mut impl VmRuntimeCtx,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    // coerce to path THEN TO STRING
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    if let Some(Path(s)) = val.as_inline::<Path>() {
+        return m.return_from_primop(Value::new_inline(s), reader);
+    }
+    let Some(s) = ctx.get_string(val) else {
+        return m.finish_err(Error::eval_error(format!(
+            "cannot coerce {} to a path",
+            val.ty()
+        )));
+    };
+    if !s.starts_with('/') {
+        return m.finish_err(Error::eval_error(format!(
+            "string '{s}' doesn't represent an absolute path"
+        )));
+    }
+    let canon = canon_path_str(s);
+    let sid = ctx.intern_string(canon);
+    m.return_from_primop(Value::new_inline(sid), reader)
+}
+
+pub fn is_path<'gc, M: Machine<'gc>>(
+    m: &mut M,
+    reader: &mut BytecodeReader<'_>,
+    mc: &Mutation<'gc>,
+) -> Step {
+    let val = m.force_and_retry::<StrictValue>(reader, mc)?;
+    let is_path = val.is::<Path>();
+    m.return_from_primop(Value::new_inline(is_path), reader)
+}

fix/Cargo.toml

@@ -3,23 +3,24 @@ name = "fix"
 version = "0.1.0"
 edition = "2024"
 
+[[bench]]
+harness = false
+name = "basic_ops"
+
+[[bench]]
+harness = false
+name = "builtins"
+
+[[bench]]
+harness = false
+name = "thunk_scope"
+
 [dependencies]
 mimalloc = "0.1"
 
-tokio = { version = "1.41", features = [
-    "rt-multi-thread",
-    "sync",
-    "net",
-    "io-util",
-] }
-nix-compat = { git = "https://git.snix.dev/snix/snix.git", version = "0.1.0", features = [
-    "wire",
-    "async",
-] }
-
 # REPL
 anyhow = "1.0"
-rustyline = "17.0"
+rustyline = "18.0"
 
 # CLI
 clap = { version = "4", features = ["derive"] }
@@ -28,77 +29,24 @@ clap = { version = "4", features = ["derive"] }
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 
-derive_more = { version = "2", features = ["full"] }
-thiserror = "2"
 miette = { version = "7.4", features = ["fancy"] }
+# Error Reporting
+thiserror = "2"
 
-hashbrown = "0.16"
+# Data Structure
-string-interner = "0.19"
+hashbrown = { workspace = true }
-bumpalo = { version = "3.20", features = [
+string-interner = { workspace = true }
-    "allocator-api2",
-    "boxed",
-    "collections",
-] }
 
-rust-embed = "8.11"
+ere = { workspace = true }
 
-regex = "1.11"
+fix-bytecode = { path = "../fix-bytecode" }
-
+fix-compiler = { path = "../fix-compiler" }
-nix-nar = "0.3"
+fix-error = { path = "../fix-error" }
-sha2 = "0.10"
+fix-lang = { path = "../fix-lang" }
-sha1 = "0.10"
+fix-runtime = { path = "../fix-runtime" }
-md5 = "0.8"
+fix-vm = { path = "../fix-vm" }
-hex = "0.4"
-
-base64 = "0.22"
-
-reqwest = { version = "0.13", features = [
-    "blocking",
-    "rustls",
-], default-features = false }
-tar = "0.4"
-flate2 = "1.0"
-xz2 = "0.1"
-bzip2 = "0.6"
-serde = { version = "1.0", features = ["derive"] }
-serde_json = "1.0"
-# spec 1.0.0
-toml = "=0.9.9"
-dirs = "6.0"
-tempfile = "3.24"
-rusqlite = { version = "0.38", features = ["bundled"] }
-
-rnix = "0.14"
-rowan = "0.16"
-
-ere = "0.2.4"
-num_enum = "0.7.5"
-tap = "1.0.1"
-
-ghost-cell = "0.2"
-colored = "3.1"
-sptr = "0.3"
-sealed = "0.6"
-small-map = "0.1"
-smallvec = "1.15"
-
-[dependencies.gc-arena]
-git = "https://github.com/kyren/gc-arena"
-rev = "75671ae03f53718357b741ed4027560f14e90836"
-features = ["allocator-api2", "hashbrown", "smallvec"]
 
 [dev-dependencies]
 criterion = { version = "0.8", features = ["html_reports"] }
+tempfile = "3.24"
 test-log = { version = "0.2", features = ["trace"] }
-
-[[bench]]
-name = "basic_ops"
-harness = false
-
-[[bench]]
-name = "builtins"
-harness = false
-
-[[bench]]
-name = "thunk_scope"
-harness = false

fix/benches/utils.rs

@@ -1,18 +1,15 @@
 #![allow(dead_code)]
 
-use fix::error::{Result, Source};
+use fix::Evaluator;
-use fix::runtime::Runtime;
+use fix_error::{Result, Source};
-use fix::value::Value;
+use fix_lang::Value;
 
 pub fn eval(expr: &str) -> Value {
-    Runtime::new()
+    Evaluator::new()
-        .unwrap()
         .eval(Source::new_eval(expr.into()).unwrap())
         .unwrap()
 }
 
 pub fn eval_result(expr: &str) -> Result<Value> {
-    Runtime::new()
+    Evaluator::new().eval(Source::new_eval(expr.into()).unwrap())
-        .unwrap()
-        .eval(Source::new_eval(expr.into()).unwrap())
 }

fix/src/ir.rs

@@ -1,260 +0,0 @@
-use std::hash::Hash;
-use std::ops::Deref;
-
-use bumpalo::Bump;
-use bumpalo::boxed::Box;
-use bumpalo::collections::Vec;
-use gc_arena::Collect;
-use ghost_cell::{GhostCell, GhostToken};
-use rnix::{TextRange, ast};
-use string_interner::symbol::SymbolU32;
-
-use crate::runtime::BuiltinId;
-
-pub type HashMap<'ir, K, V> = hashbrown::HashMap<K, V, hashbrown::DefaultHashBuilder, &'ir Bump>;
-
-#[repr(transparent)]
-#[derive(Clone, Copy)]
-pub struct IrRef<'id, 'ir>(&'ir GhostCell<'id, Ir<'ir, Self>>);
-
-impl<'id, 'ir> IrRef<'id, 'ir> {
-    pub fn new(ir: &'ir GhostCell<'id, Ir<'ir, Self>>) -> Self {
-        Self(ir)
-    }
-
-    pub fn alloc(bump: &'ir Bump, ir: Ir<'ir, Self>) -> Self {
-        Self(bump.alloc(GhostCell::new(ir)))
-    }
-
-    pub fn borrow<'a>(&'a self, token: &'a GhostToken<'id>) -> &'a Ir<'ir, Self> {
-        self.0.borrow(token)
-    }
-
-    /// Freeze a mutable IR reference into a read-only one, consuming the
-    /// `GhostToken` to prevent any further mutation.
-    ///
-    /// # Safety
-    /// The transmute is sound because:
-    /// - `GhostCell<'id, T>` is `#[repr(transparent)]` over `T`
-    /// - `IrRef<'id, 'ir>` is `#[repr(transparent)]` over
-    ///   `&'ir GhostCell<'id, Ir<'ir, Self>>`
-    /// - `RawIrRef<'ir>` is `#[repr(transparent)]` over `&'ir Ir<'ir, Self>`
-    /// - `Ir<'ir, Ref>` is `#[repr(C)]` and both ref types are pointer-sized
-    ///
-    /// Consuming the `GhostToken` guarantees no `borrow_mut` calls can occur
-    /// afterwards, so the shared `&Ir` references from `RawIrRef::Deref` can
-    /// never alias with mutable references.
-    pub fn freeze(self, _token: GhostToken<'id>) -> RawIrRef<'ir> {
-        unsafe { std::mem::transmute(self) }
-    }
-}
-
-#[repr(transparent)]
-#[derive(Clone, Copy, Debug)]
-pub struct RawIrRef<'ir>(pub &'ir Ir<'ir, Self>);
-
-impl<'ir> Deref for RawIrRef<'ir> {
-    type Target = Ir<'ir, RawIrRef<'ir>>;
-    fn deref(&self) -> &Self::Target {
-        self.0
-    }
-}
-
-#[repr(C)]
-#[derive(Debug)]
-pub enum Ir<'ir, Ref> {
-    Int(i64),
-    Float(f64),
-    Bool(bool),
-    Null,
-    Str(Box<'ir, String>),
-    AttrSet {
-        stcs: HashMap<'ir, StringId, (Ref, TextRange)>,
-        dyns: Vec<'ir, (Ref, Ref, TextRange)>,
-    },
-    List {
-        items: Vec<'ir, Ref>,
-    },
-    Path(Ref),
-    ConcatStrings {
-        parts: Vec<'ir, Ref>,
-        force_string: bool,
-    },
-
-    // OPs
-    UnOp {
-        rhs: Ref,
-        kind: UnOpKind,
-    },
-    BinOp {
-        lhs: Ref,
-        rhs: Ref,
-        kind: BinOpKind,
-    },
-    HasAttr {
-        lhs: Ref,
-        rhs: Vec<'ir, Attr<Ref>>,
-    },
-    Select {
-        expr: Ref,
-        attrpath: Vec<'ir, Attr<Ref>>,
-        default: Option<Ref>,
-        span: TextRange,
-    },
-
-    // Conditionals
-    If {
-        cond: Ref,
-        consq: Ref,
-        alter: Ref,
-    },
-    Assert {
-        assertion: Ref,
-        expr: Ref,
-        assertion_raw: String,
-        span: TextRange,
-    },
-
-    With {
-        namespace: Ref,
-        body: Ref,
-        thunks: Vec<'ir, (ThunkId, Ref)>,
-    },
-    WithLookup(StringId),
-
-    // Function related
-    Func {
-        body: Ref,
-        param: Option<Param<'ir>>,
-        thunks: Vec<'ir, (ThunkId, Ref)>,
-    },
-    Arg {
-        layer: usize,
-    },
-    Call {
-        func: Ref,
-        arg: Ref,
-        span: TextRange,
-    },
-
-    // Builtins
-    Builtins,
-    Builtin(BuiltinId),
-    BuiltinConst(StringId),
-
-    // Misc
-    TopLevel {
-        body: Ref,
-        thunks: Vec<'ir, (ThunkId, Ref)>,
-    },
-    Thunk(ThunkId),
-    CurPos(TextRange),
-    ReplBinding(StringId),
-    ScopedImportBinding(StringId),
-}
-
-#[repr(transparent)]
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
-pub struct ThunkId(pub usize);
-
-#[repr(transparent)]
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Collect)]
-#[collect(require_static)]
-pub struct StringId(pub SymbolU32);
-
-#[repr(transparent)]
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
-pub struct SpanId(pub u32);
-
-/// Represents a key in an attribute path.
-#[allow(unused)]
-#[derive(Debug)]
-pub enum Attr<Ref> {
-    /// A dynamic attribute key, which is an expression that must evaluate to a string.
-    /// Example: `attrs.${key}`
-    Dynamic(Ref, TextRange),
-    /// A static attribute key.
-    /// Example: `attrs.key`
-    Str(StringId, TextRange),
-}
-
-/// The kinds of binary operations supported in Nix.
-#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
-pub enum BinOpKind {
-    // Arithmetic
-    Add,
-    Sub,
-    Div,
-    Mul,
-
-    // Comparison
-    Eq,
-    Neq,
-    Lt,
-    Gt,
-    Leq,
-    Geq,
-
-    // Logical
-    And,
-    Or,
-    Impl,
-
-    // Set/String/Path operations
-    Con, // List concatenation (`++`)
-    Upd, // AttrSet update (`//`)
-
-    // Not standard, but part of rnix AST
-    PipeL,
-    PipeR,
-}
-
-impl From<ast::BinOpKind> for BinOpKind {
-    fn from(op: ast::BinOpKind) -> Self {
-        use BinOpKind::*;
-        use ast::BinOpKind as kind;
-        match op {
-            kind::Concat => Con,
-            kind::Update => Upd,
-            kind::Add => Add,
-            kind::Sub => Sub,
-            kind::Mul => Mul,
-            kind::Div => Div,
-            kind::And => And,
-            kind::Equal => Eq,
-            kind::Implication => Impl,
-            kind::Less => Lt,
-            kind::LessOrEq => Leq,
-            kind::More => Gt,
-            kind::MoreOrEq => Geq,
-            kind::NotEqual => Neq,
-            kind::Or => Or,
-            kind::PipeLeft => PipeL,
-            kind::PipeRight => PipeR,
-        }
-    }
-}
-
-/// The kinds of unary operations.
-#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
-pub enum UnOpKind {
-    Neg, // Negation (`-`)
-    Not, // Logical not (`!`)
-}
-
-impl From<ast::UnaryOpKind> for UnOpKind {
-    fn from(value: ast::UnaryOpKind) -> Self {
-        match value {
-            ast::UnaryOpKind::Invert => UnOpKind::Not,
-            ast::UnaryOpKind::Negate => UnOpKind::Neg,
-        }
-    }
-}
-
-/// Describes the parameters of a function.
-#[derive(Debug)]
-pub struct Param<'ir> {
-    pub required: Vec<'ir, (StringId, TextRange)>,
-    pub optional: Vec<'ir, (StringId, TextRange)>,
-    pub ellipsis: bool,
-}

fix/src/lib.rs

@@ -1,22 +1,153 @@
 #![warn(clippy::unwrap_used)]
 #![allow(dead_code)]
 
-mod boxing;
+use fix_bytecode::InstructionPtr;
-pub mod error;
+use fix_bytecode::disassembler::{Disassembler, DisassemblerContext};
-pub mod logging;
+use fix_compiler::{CodeState, ExtraScope};
-pub mod runtime;
+use fix_error::{Result, Source};
-pub mod value;
+use fix_lang::StringId;
+use fix_runtime::{ForceMode, StaticValue, VmCode, VmContext, VmRuntimeCtx};
+use fix_vm::Vm;
+use hashbrown::{HashMap, HashSet};
+use string_interner::{DefaultStringInterner, Symbol as _};
 
-mod codegen;
 mod derivation;
-mod disassembler;
+pub mod logging;
-mod downgrade;
-// mod fetcher;
-mod ir;
-mod nar;
-mod nix_utils;
-mod store;
-mod string_context;
 
 #[global_allocator]
 static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc;
+
+pub struct RuntimeState {
+    pub strings: DefaultStringInterner,
+    pub constants: Constants,
+}
+
+pub struct Evaluator {
+    pub runtime: RuntimeState,
+    pub code: CodeState,
+}
+
+impl Default for Evaluator {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Evaluator {
+    pub fn new() -> Self {
+        let mut strings = DefaultStringInterner::new();
+        let code = CodeState::new(&mut strings);
+        Self {
+            runtime: RuntimeState {
+                strings,
+                constants: Constants::default(),
+            },
+            code,
+        }
+    }
+
+    pub fn eval(&mut self, source: Source) -> Result<fix_lang::Value> {
+        self.do_eval(source, None, ForceMode::AsIs)
+    }
+
+    pub fn eval_shallow(&mut self, source: Source) -> Result<fix_lang::Value> {
+        self.do_eval(source, None, ForceMode::Shallow)
+    }
+
+    pub fn eval_deep(&mut self, source: Source) -> Result<fix_lang::Value> {
+        self.do_eval(source, None, ForceMode::Deep)
+    }
+
+    pub fn eval_repl(
+        &mut self,
+        source: Source,
+        scope: &HashSet<StringId>,
+    ) -> Result<fix_lang::Value> {
+        self.do_eval(source, Some(ExtraScope::Repl(scope)), ForceMode::Shallow)
+    }
+
+    fn do_eval<'ctx>(
+        &'ctx mut self,
+        source: Source,
+        extra_scope: Option<ExtraScope<'ctx>>,
+        force_mode: ForceMode,
+    ) -> Result<fix_lang::Value> {
+        let ip = self
+            .code
+            .compile_bytecode(source, extra_scope, &mut self.runtime)?;
+        Vm::run(self, ip, force_mode)
+    }
+
+    pub fn add_binding(
+        &mut self,
+        _ident: &str,
+        _expr: &str,
+        _scope: &mut HashSet<StringId>,
+    ) -> Result<fix_lang::Value> {
+        todo!("add_binding")
+    }
+
+    pub fn compile_bytecode(&mut self, source: Source) -> Result<InstructionPtr> {
+        self.code.compile_bytecode(source, None, &mut self.runtime)
+    }
+
+    pub fn disassemble_colored(&self, ip: InstructionPtr) -> String {
+        Disassembler::new(ip, self).disassemble_colored()
+    }
+}
+
+impl VmRuntimeCtx for RuntimeState {
+    fn intern_string(&mut self, s: impl AsRef<str>) -> StringId {
+        StringId(self.strings.get_or_intern(s))
+    }
+    fn resolve_string(&self, id: StringId) -> &str {
+        #[allow(clippy::unwrap_used)]
+        self.strings.resolve(id.0).unwrap()
+    }
+    fn get_const(&self, id: u32) -> StaticValue {
+        #[allow(clippy::unwrap_used)]
+        self.constants.get(id).unwrap()
+    }
+    fn add_const(&mut self, val: StaticValue) -> u32 {
+        self.constants.insert(val)
+    }
+}
+
+impl VmContext for Evaluator {
+    fn split(&mut self) -> (&mut impl VmCode, &mut impl VmRuntimeCtx) {
+        (&mut self.code, &mut self.runtime)
+    }
+}
+
+#[derive(Default)]
+pub struct Constants {
+    data: Vec<StaticValue>,
+    dedup: HashMap<u64, u32>,
+}
+
+impl Constants {
+    fn insert(&mut self, val: StaticValue) -> u32 {
+        let bits = val.to_bits();
+        *self.dedup.entry(bits).or_insert_with(|| {
+            let idx = self.data.len() as u32;
+            self.data.push(val);
+            idx
+        })
+    }
+
+    fn get(&self, id: u32) -> Option<StaticValue> {
+        self.data.get(id as usize).copied()
+    }
+}
+
+impl DisassemblerContext for Evaluator {
+    fn get_code(&self) -> &[u8] {
+        &self.code.bytecode
+    }
+
+    #[allow(clippy::unwrap_used)]
+    fn resolve_string(&self, id: u32) -> &str {
+        let id = string_interner::symbol::SymbolU32::try_from_usize(id as usize).unwrap();
+        self.runtime.strings.resolve(id).unwrap()
+    }
+}

fix/src/main.rs

@@ -3,8 +3,8 @@ use std::process::exit;
 
 use anyhow::Result;
 use clap::{Args, Parser, Subcommand};
-use fix::error::Source;
+use fix::Evaluator;
-use fix::runtime::Runtime;
+use fix_error::Source;
 use hashbrown::HashSet;
 use rustyline::DefaultEditor;
 use rustyline::error::ReadlineError;
@@ -40,7 +40,7 @@ struct ExprSource {
     file: Option<PathBuf>,
 }
 
-fn run_compile(runtime: &mut Runtime, src: ExprSource, silent: bool) -> Result<()> {
+fn run_compile(eval: &mut Evaluator, src: ExprSource, silent: bool) -> Result<()> {
     let src = if let Some(expr) = src.expr {
         Source::new_eval(expr)?
     } else if let Some(file) = src.file {
@@ -48,10 +48,10 @@ fn run_compile(runtime: &mut Runtime, src: ExprSource, silent: bool) -> Result<(
     } else {
         unreachable!()
     };
-    match runtime.compile_bytecode(src) {
+    match eval.compile_bytecode(src) {
         Ok(ip) => {
             if !silent {
-                println!("{}", runtime.disassemble_colored(ip));
+                println!("{}", eval.disassemble_colored(ip));
             }
         }
         Err(err) => {
@@ -62,7 +62,7 @@ fn run_compile(runtime: &mut Runtime, src: ExprSource, silent: bool) -> Result<(
     Ok(())
 }
 
-fn run_eval(runtime: &mut Runtime, src: ExprSource) -> Result<()> {
+fn run_eval(eval: &mut Evaluator, src: ExprSource) -> Result<()> {
     let src = if let Some(expr) = src.expr {
         Source::new_eval(expr)?
     } else if let Some(file) = src.file {
@@ -70,7 +70,7 @@ fn run_eval(runtime: &mut Runtime, src: ExprSource) -> Result<()> {
     } else {
         unreachable!()
     };
-    match runtime.eval_deep(src) {
+    match eval.eval_deep(src) {
         Ok(value) => {
             println!("{}", value.display_compat());
         }
@@ -82,12 +82,12 @@ fn run_eval(runtime: &mut Runtime, src: ExprSource) -> Result<()> {
     Ok(())
 }
 
-fn run_repl(runtime: &mut Runtime) -> Result<()> {
+fn run_repl(eval: &mut Evaluator) -> Result<()> {
     let mut rl = DefaultEditor::new()?;
     let mut scope = HashSet::new();
     const RE: ere::Regex<3> = ere::compile_regex!("^[ \t]*([a-zA-Z_][a-zA-Z0-9_'-]*)[ \t]*(.*)$");
     loop {
-        let readline = rl.readline("nix-js-repl> ");
+        let readline = rl.readline("fix-repl> ");
         match readline {
             Ok(line) => {
                 if line.trim().is_empty() {
@@ -101,20 +101,20 @@ fn run_repl(runtime: &mut Runtime) -> Result<()> {
                             eprintln!("Error: missing expression after '='");
                             continue;
                         }
-                        match runtime.add_binding(ident, expr, &mut scope) {
+                        match eval.add_binding(ident, expr, &mut scope) {
                             Ok(value) => println!("{} = {}", ident, value),
                             Err(err) => eprintln!("{:?}", miette::Report::new(*err)),
                         }
                     } else {
                         let src = Source::new_repl(line)?;
-                        match runtime.eval_repl(src, &scope) {
+                        match eval.eval_repl(src, &scope) {
                             Ok(value) => println!("{value}"),
                             Err(err) => eprintln!("{:?}", miette::Report::new(*err)),
                         }
                     }
                 } else {
                     let src = Source::new_repl(line)?;
-                    match runtime.eval_repl(src, &scope) {
+                    match eval.eval_repl(src, &scope) {
                         Ok(value) => println!("{value}"),
                         Err(err) => eprintln!("{:?}", miette::Report::new(*err)),
                     }
@@ -141,11 +141,11 @@ fn main() -> Result<()> {
 
     let cli = Cli::parse();
 
-    let mut runtime = Runtime::new()?;
+    let mut eval = Evaluator::new();
 
     match cli.command {
-        Command::Compile { source, silent } => run_compile(&mut runtime, source, silent),
+        Command::Compile { source, silent } => run_compile(&mut eval, source, silent),
-        Command::Eval { source } => run_eval(&mut runtime, source),
+        Command::Eval { source } => run_eval(&mut eval, source),
-        Command::Repl => run_repl(&mut runtime),
+        Command::Repl => run_repl(&mut eval),
     }
 }

fix/src/nar.rs

@@ -4,7 +4,7 @@ use std::path::Path;
 use nix_nar::Encoder;
 use sha2::{Digest, Sha256};
 
-use crate::error::{Error, Result};
+use fix_error::{Error, Result};
 
 pub fn compute_nar_hash(path: &Path) -> Result<[u8; 32]> {
     let mut hasher = Sha256::new();

fix/src/runtime.rs

@@ -1,559 +0,0 @@
-use bumpalo::Bump;
-use gc_arena::{Arena, Rootable};
-use ghost_cell::{GhostCell, GhostToken};
-use hashbrown::{HashMap, HashSet};
-use rnix::TextRange;
-use string_interner::symbol::SymbolU32;
-use string_interner::{DefaultStringInterner, Symbol as _};
-
-use crate::codegen::{BytecodeContext, InstructionPtr};
-use crate::disassembler::{Disassembler, DisassemblerContext};
-use crate::downgrade::{Downgrade as _, DowngradeContext};
-use crate::error::{Error, Result, Source};
-use crate::ir::{Ir, IrRef, RawIrRef, StringId, ThunkId};
-use crate::runtime::builtins::init_builtins;
-use crate::runtime::value::StaticValue;
-use crate::runtime::vm::{ForceMode, new_gc_root};
-use crate::store::{DaemonStore, StoreConfig};
-use crate::value::Symbol;
-
-mod builtins;
-mod stack;
-pub(crate) mod value;
-mod vm;
-pub(crate) use builtins::{BUILTINS, BuiltinId};
-use stack::Stack;
-use vm::{ErrorFrame, GcRoot};
-
-pub struct Runtime {
-    // global
-    sources: Vec<Source>,
-    spans: Vec<(usize, TextRange)>,
-    store: DaemonStore,
-    strings: DefaultStringInterner,
-    // FIXME: remove?
-    thunk_count: usize,
-    bytecode: Vec<u8>,
-    pub(crate) constants: Vec<StaticValue>,
-    constant_dedup: HashMap<u64, u32>,
-
-    // downgrade
-    global_env: HashMap<StringId, Ir<'static, RawIrRef<'static>>>,
-
-    // eval
-    pc: usize,
-    fuel: usize,
-    error_contexts: Stack<8192, ErrorFrame>,
-    arena: Arena<Rootable![GcRoot<'_>]>,
-    force_mode: ForceMode,
-}
-
-impl Runtime {
-    const DEFAULT_FUEL_AMOUNT: usize = 2048;
-
-    pub fn new() -> Result<Self> {
-        // HACK: what the heck...
-        let mut global_env = HashMap::new();
-        let mut strings = DefaultStringInterner::new();
-        let arena = Arena::new(|mc| {
-            let (root, env) = new_gc_root(mc, &mut strings);
-            global_env = env;
-            root
-        });
-
-        let config = StoreConfig::from_env();
-        let store = DaemonStore::connect(&config.daemon_socket)?;
-
-        Ok(Self {
-            sources: Vec::new(),
-            spans: Vec::new(),
-            store,
-            strings,
-            thunk_count: 0,
-            bytecode: Vec::new(),
-            constants: Vec::new(),
-            constant_dedup: HashMap::new(),
-
-            global_env,
-
-            pc: 0,
-            fuel: Self::DEFAULT_FUEL_AMOUNT,
-            error_contexts: Stack::new(),
-            arena,
-            force_mode: ForceMode::default(),
-        })
-    }
-
-    pub fn eval(&mut self, source: Source) -> Result<crate::value::Value> {
-        self.do_eval(source, None, ForceMode::AsIs)
-    }
-
-    pub fn eval_shallow(&mut self, source: Source) -> Result<crate::value::Value> {
-        self.do_eval(source, None, ForceMode::Shallow)
-    }
-
-    pub fn eval_deep(&mut self, source: Source) -> Result<crate::value::Value> {
-        self.do_eval(source, None, ForceMode::Deep)
-    }
-
-    pub fn eval_repl(
-        &mut self,
-        source: Source,
-        scope: &HashSet<StringId>,
-    ) -> Result<crate::value::Value> {
-        self.do_eval(source, Some(Scope::Repl(scope)), ForceMode::Shallow)
-    }
-
-    fn do_eval<'ctx>(
-        &'ctx mut self,
-        source: Source,
-        extra_scope: Option<Scope<'ctx>>,
-        force_mode: ForceMode,
-    ) -> Result<crate::value::Value> {
-        let root = self.downgrade(source, extra_scope)?;
-        let ip = crate::codegen::compile_bytecode(root.as_ref(), self);
-        self.run(ip, force_mode)
-    }
-
-    pub fn add_binding(
-        &mut self,
-        _ident: &str,
-        _expr: &str,
-        _scope: &mut HashSet<StringId>,
-    ) -> Result<crate::value::Value> {
-        todo!()
-    }
-
-    pub fn compile_bytecode(&mut self, source: Source) -> Result<InstructionPtr> {
-        let root = self.downgrade(source, None)?;
-        let ip = crate::codegen::compile_bytecode(root.as_ref(), self);
-        Ok(ip)
-    }
-
-    pub fn disassemble_colored(&mut self, ip: InstructionPtr) -> String {
-        Disassembler::new(ip, self).disassemble_colored()
-    }
-
-    pub fn disassemble(&mut self, ip: InstructionPtr) -> String {
-        Disassembler::new(ip, self).disassemble()
-    }
-
-    fn downgrade_ctx<'a, 'bump, 'id>(
-        &'a mut self,
-        bump: &'bump Bump,
-        token: GhostToken<'id>,
-        extra_scope: Option<Scope<'a>>,
-    ) -> DowngradeCtx<'a, 'id, 'bump> {
-        let Runtime {
-            global_env,
-            sources,
-            thunk_count,
-            strings,
-            ..
-        } = self;
-        DowngradeCtx {
-            bump,
-            token,
-            strings,
-            source: sources.last().expect("no current source").clone(),
-            scopes: [Scope::Global(global_env)]
-                .into_iter()
-                .chain(extra_scope)
-                .collect(),
-            with_scope_count: 0,
-            arg_count: 0,
-            thunk_count,
-            thunk_scopes: vec![ThunkScope::new_in(bump)],
-        }
-    }
-
-    fn downgrade<'a>(
-        &'a mut self,
-        source: Source,
-        extra_scope: Option<Scope<'a>>,
-    ) -> Result<OwnedIr> {
-        tracing::debug!("Parsing Nix expression");
-
-        self.sources.push(source.clone());
-
-        let root = rnix::Root::parse(&source.src);
-        handle_parse_error(root.errors(), source).map_or(Ok(()), Err)?;
-
-        tracing::debug!("Downgrading Nix expression");
-        let expr = root
-            .tree()
-            .expr()
-            .ok_or_else(|| Error::parse_error("unexpected EOF".into()))?;
-        let bump = Bump::new();
-        GhostToken::new(|token| {
-            let ir = self
-                .downgrade_ctx(&bump, token, extra_scope)
-                .downgrade_toplevel(expr)?;
-            let ir = unsafe { std::mem::transmute::<RawIrRef<'_>, RawIrRef<'static>>(ir) };
-            Ok(OwnedIr { _bump: bump, ir })
-        })
-    }
-}
-
-fn parse_error_span(error: &rnix::ParseError) -> Option<rnix::TextRange> {
-    use rnix::ParseError::*;
-    match error {
-        Unexpected(range)
-        | UnexpectedExtra(range)
-        | UnexpectedWanted(_, range, _)
-        | UnexpectedDoubleBind(range)
-        | DuplicatedArgs(range, _) => Some(*range),
-        _ => None,
-    }
-}
-
-fn handle_parse_error<'a>(
-    errors: impl IntoIterator<Item = &'a rnix::ParseError>,
-    source: Source,
-) -> Option<Box<Error>> {
-    for err in errors {
-        if let Some(span) = parse_error_span(err) {
-            return Some(
-                Error::parse_error(err.to_string())
-                    .with_source(source)
-                    .with_span(span),
-            );
-        }
-    }
-    None
-}
-
-struct DowngradeCtx<'ctx, 'id, 'ir> {
-    bump: &'ir Bump,
-    token: GhostToken<'id>,
-    strings: &'ctx mut DefaultStringInterner,
-    source: Source,
-    scopes: Vec<Scope<'ctx>>,
-    with_scope_count: u32,
-    arg_count: u32,
-    thunk_count: &'ctx mut usize,
-    thunk_scopes: Vec<ThunkScope<'id, 'ir>>,
-}
-
-fn should_thunk<'id>(ir: IrRef<'id, '_>, token: &GhostToken<'id>) -> bool {
-    !matches!(
-        ir.borrow(token),
-        Ir::Builtin(_)
-            | Ir::Builtins
-            | Ir::Int(_)
-            | Ir::Float(_)
-            | Ir::Bool(_)
-            | Ir::Null
-            | Ir::Str(_)
-            | Ir::Thunk(_)
-    )
-}
-
-impl<'ctx, 'id, 'ir> DowngradeCtx<'ctx, 'id, 'ir> {
-    fn new(
-        bump: &'ir Bump,
-        token: GhostToken<'id>,
-        symbols: &'ctx mut DefaultStringInterner,
-        global: &'ctx HashMap<StringId, Ir<'static, RawIrRef<'static>>>,
-        extra_scope: Option<Scope<'ctx>>,
-        thunk_count: &'ctx mut usize,
-        source: Source,
-    ) -> Self {
-        Self {
-            bump,
-            token,
-            strings: symbols,
-            source,
-            scopes: std::iter::once(Scope::Global(global))
-                .chain(extra_scope)
-                .collect(),
-            thunk_count,
-            arg_count: 0,
-            with_scope_count: 0,
-            thunk_scopes: vec![ThunkScope::new_in(bump)],
-        }
-    }
-}
-
-impl<'ctx: 'ir, 'id, 'ir> DowngradeContext<'id, 'ir> for DowngradeCtx<'ctx, 'id, 'ir> {
-    fn new_expr(&self, expr: Ir<'ir, IrRef<'id, 'ir>>) -> IrRef<'id, 'ir> {
-        IrRef::new(self.bump.alloc(GhostCell::new(expr)))
-    }
-
-    fn maybe_thunk(&mut self, ir: IrRef<'id, 'ir>) -> IrRef<'id, 'ir> {
-        if !should_thunk(ir, &self.token) {
-            return ir;
-        }
-
-        let id = ThunkId(*self.thunk_count);
-        *self.thunk_count = self.thunk_count.checked_add(1).expect("thunk id overflow");
-        self.thunk_scopes
-            .last_mut()
-            .expect("no active cache scope")
-            .add_binding(id, ir, &self.token);
-        IrRef::alloc(self.bump, Ir::Thunk(id))
-    }
-
-    fn new_sym(&mut self, sym: String) -> StringId {
-        StringId(self.strings.get_or_intern(sym))
-    }
-
-    fn get_sym(&self, id: StringId) -> Symbol<'_> {
-        self.strings.resolve(id.0).expect("no symbol found").into()
-    }
-
-    fn lookup(&self, sym: StringId, span: TextRange) -> Result<IrRef<'id, 'ir>> {
-        for scope in self.scopes.iter().rev() {
-            match scope {
-                &Scope::Global(global_scope) => {
-                    if let Some(expr) = global_scope.get(&sym) {
-                        let ir = match expr {
-                            Ir::Builtins => Ir::Builtins,
-                            Ir::Builtin(s) => Ir::Builtin(*s),
-                            Ir::Bool(b) => Ir::Bool(*b),
-                            Ir::Null => Ir::Null,
-                            _ => unreachable!("globals should only contain leaf IR nodes"),
-                        };
-                        return Ok(self.new_expr(ir));
-                    }
-                }
-                &Scope::Repl(repl_bindings) => {
-                    if repl_bindings.contains(&sym) {
-                        return Ok(self.new_expr(Ir::ReplBinding(sym)));
-                    }
-                }
-                Scope::ScopedImport(scoped_bindings) => {
-                    if scoped_bindings.contains(&sym) {
-                        return Ok(self.new_expr(Ir::ScopedImportBinding(sym)));
-                    }
-                }
-                Scope::Let(let_scope) => {
-                    if let Some(&expr) = let_scope.get(&sym) {
-                        return Ok(self.new_expr(Ir::Thunk(expr)));
-                    }
-                }
-                &Scope::Param {
-                    sym: param_sym,
-                    abs_layer,
-                } => {
-                    if param_sym == sym {
-                        return Ok(self.new_expr(Ir::Arg {
-                            layer: self.thunk_scopes.len() - abs_layer,
-                        }));
-                    }
-                }
-            }
-        }
-
-        if self.with_scope_count > 0 {
-            Ok(self.new_expr(Ir::WithLookup(sym)))
-        } else {
-            Err(Error::downgrade_error(
-                format!("'{}' not found", self.get_sym(sym)),
-                self.get_current_source(),
-                span,
-            ))
-        }
-    }
-
-    fn get_current_source(&self) -> Source {
-        self.source.clone()
-    }
-
-    fn with_let_scope<F, R>(&mut self, keys: &[StringId], f: F) -> Result<R>
-    where
-        F: FnOnce(&mut Self) -> Result<(bumpalo::collections::Vec<'ir, IrRef<'id, 'ir>>, R)>,
-    {
-        let base = *self.thunk_count;
-        *self.thunk_count = self
-            .thunk_count
-            .checked_add(keys.len())
-            .expect("thunk id overflow");
-        let iter = keys.iter().enumerate().map(|(offset, &key)| {
-            (
-                key,
-                ThunkId(unsafe { base.checked_add(offset).unwrap_unchecked() }),
-            )
-        });
-        self.scopes.push(Scope::Let(iter.collect()));
-        let (vals, ret) = {
-            let mut guard = ScopeGuard { ctx: self };
-            f(guard.as_ctx())?
-        };
-        assert_eq!(keys.len(), vals.len());
-        let scope = self.thunk_scopes.last_mut().expect("no active thunk scope");
-        scope.extend_bindings((base..base + keys.len()).map(ThunkId).zip(vals));
-        Ok(ret)
-    }
-
-    fn with_param_scope<F, R>(&mut self, sym: StringId, f: F) -> R
-    where
-        F: FnOnce(&mut Self) -> R,
-    {
-        self.scopes.push(Scope::Param {
-            sym,
-            abs_layer: self.thunk_scopes.len(),
-        });
-        let mut guard = ScopeGuard { ctx: self };
-        f(guard.as_ctx())
-    }
-
-    fn with_with_scope<F, R>(&mut self, f: F) -> R
-    where
-        F: FnOnce(&mut Self) -> R,
-    {
-        self.with_scope_count += 1;
-        let ret = f(self);
-        self.with_scope_count -= 1;
-        ret
-    }
-
-    fn with_thunk_scope<F, R>(
-        &mut self,
-        f: F,
-    ) -> (
-        R,
-        bumpalo::collections::Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>,
-    )
-    where
-        F: FnOnce(&mut Self) -> R,
-    {
-        self.thunk_scopes.push(ThunkScope::new_in(self.bump));
-        let ret = f(self);
-        (
-            ret,
-            self.thunk_scopes
-                .pop()
-                .expect("no thunk scope left???")
-                .bindings,
-        )
-    }
-
-    fn bump(&self) -> &'ir bumpalo::Bump {
-        self.bump
-    }
-}
-
-impl<'id, 'ir, 'ctx: 'ir> DowngradeCtx<'ctx, 'id, 'ir> {
-    fn downgrade_toplevel(mut self, root: rnix::ast::Expr) -> Result<RawIrRef<'ir>> {
-        let body = root.downgrade(&mut self)?;
-        let thunks = self
-            .thunk_scopes
-            .pop()
-            .expect("no thunk scope left???")
-            .bindings;
-        let ir = IrRef::alloc(self.bump, Ir::TopLevel { body, thunks });
-        Ok(ir.freeze(self.token))
-    }
-}
-
-struct ThunkScope<'id, 'ir> {
-    bindings: bumpalo::collections::Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>,
-}
-
-impl<'id, 'ir> ThunkScope<'id, 'ir> {
-    fn new_in(bump: &'ir Bump) -> Self {
-        Self {
-            bindings: bumpalo::collections::Vec::new_in(bump),
-        }
-    }
-
-    fn add_binding(&mut self, id: ThunkId, ir: IrRef<'id, 'ir>, _token: &GhostToken<'id>) {
-        self.bindings.push((id, ir));
-    }
-
-    fn extend_bindings(&mut self, iter: impl IntoIterator<Item = (ThunkId, IrRef<'id, 'ir>)>) {
-        self.bindings.extend(iter);
-    }
-}
-
-enum Scope<'ctx> {
-    Global(&'ctx HashMap<StringId, Ir<'static, RawIrRef<'static>>>),
-    Repl(&'ctx HashSet<StringId>),
-    ScopedImport(HashSet<StringId>),
-    Let(HashMap<StringId, ThunkId>),
-    Param { sym: StringId, abs_layer: usize },
-}
-
-struct ScopeGuard<'a, 'ctx, 'id, 'ir> {
-    ctx: &'a mut DowngradeCtx<'ctx, 'id, 'ir>,
-}
-
-impl Drop for ScopeGuard<'_, '_, '_, '_> {
-    fn drop(&mut self) {
-        self.ctx.scopes.pop();
-    }
-}
-
-impl<'id, 'ir, 'ctx> ScopeGuard<'_, 'ctx, 'id, 'ir> {
-    fn as_ctx(&mut self) -> &mut DowngradeCtx<'ctx, 'id, 'ir> {
-        self.ctx
-    }
-}
-
-struct OwnedIr {
-    _bump: Bump,
-    ir: RawIrRef<'static>,
-}
-
-impl OwnedIr {
-    unsafe fn new(ir: RawIrRef<'_>, bump: Bump) -> Self {
-        Self {
-            _bump: bump,
-            ir: unsafe { std::mem::transmute::<RawIrRef<'_>, RawIrRef<'static>>(ir) },
-        }
-    }
-
-    fn as_ref(&self) -> RawIrRef<'_> {
-        self.ir
-    }
-}
-
-impl BytecodeContext for Runtime {
-    fn intern_string(&mut self, s: &str) -> StringId {
-        StringId(self.strings.get_or_intern(s))
-    }
-
-    fn register_span(&mut self, range: TextRange) -> u32 {
-        let id = self.spans.len();
-        let source_id = self
-            .sources
-            .len()
-            .checked_sub(1)
-            .expect("current_source not set");
-        self.spans.push((source_id, range));
-        id as u32
-    }
-
-    fn get_code(&self) -> &[u8] {
-        &self.bytecode
-    }
-
-    fn get_code_mut(&mut self) -> &mut Vec<u8> {
-        &mut self.bytecode
-    }
-
-    fn add_constant(&mut self, val: StaticValue) -> u32 {
-        let bits = val.to_bits();
-        *self.constant_dedup.entry(bits).or_insert_with(|| {
-            let idx = self.constants.len() as u32;
-            self.constants.push(val);
-            idx
-        })
-    }
-}
-
-impl DisassemblerContext for Runtime {
-    fn lookup_string(&self, id: u32) -> &str {
-        self.strings
-            .resolve(SymbolU32::try_from_usize(id as usize).expect("invalid string id"))
-            .expect("string not found")
-    }
-    fn get_code(&self) -> &[u8] {
-        &self.bytecode
-    }
-}
-
-struct WellKnownSymbols {
-    // TODO:
-}

fix/src/runtime/builtins.rs

@@ -1,410 +0,0 @@
-use gc_arena::{Collect, Gc, Mutation, RefLock};
-use hashbrown::HashMap;
-use num_enum::TryFromPrimitive;
-use smallvec::SmallVec;
-use string_interner::DefaultStringInterner;
-use string_interner::symbol::SymbolU32;
-
-use super::value::*;
-use crate::ir::{Ir, RawIrRef, StringId};
-
-/// Generates both the BUILTINS const table and the BuiltinId enum
-/// from a single source of truth, preventing index desync.
-macro_rules! define_builtins {
-    ($(($name:literal, $variant:ident, $arity:expr)),* $(,)?) => {
-        /// Builtin function registry.
-        /// Array index IS the PrimOp id. (name, arity) pairs.
-        pub(crate) const BUILTINS: &[(&str, u8)] = &[
-            $(($name, $arity),)*
-        ];
-
-        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, TryFromPrimitive, Collect)]
-        #[repr(u8)]
-        #[collect(require_static)]
-        pub(crate) enum BuiltinId {
-            $($variant,)*
-        }
-    };
-}
-
-define_builtins! {
-    ("abort",                    Abort,                    1),
-    ("__add",                      Add,                      2),
-    ("__addErrorContext",          AddErrorContext,           2),
-    ("__all",                      All,                      2),
-    ("__any",                      Any,                      2),
-    ("__appendContext",            AppendContext,             2),
-    ("__attrNames",                AttrNames,                1),
-    ("__attrValues",               AttrValues,               1),
-    ("baseNameOf",               BaseNameOf,               1),
-    ("__bitAnd",                   BitAnd,                   2),
-    ("__bitOr",                    BitOr,                    2),
-    ("__bitXor",                   BitXor,                   2),
-    ("break",                    Break,                    1),
-    ("__catAttrs",                 CatAttrs,                 2),
-    ("__ceil",                     Ceil,                     1),
-    ("__compareVersions",          CompareVersions,          2),
-    ("__concatLists",              ConcatLists,              1),
-    ("__concatMap",                ConcatMap,                2),
-    ("__concatStringsSep",         ConcatStringsSep,         2),
-    ("__convertHash",              ConvertHash,              1),
-    ("__deepSeq",                  DeepSeq,                  2),
-    ("derivation",               Derivation,               1),
-    ("derivationStrict",         DerivationStrict,         1),
-    ("dirOf",                    DirOf,                    1),
-    ("__div",                      Div,                      2),
-    ("__elem",                     Elem,                     2),
-    ("__elemAt",                   ElemAt,                   2),
-    ("fetchGit",                 FetchGit,                 1),
-    ("fetchMercurial",           FetchMercurial,           1),
-    ("fetchTarball",             FetchTarball,             1),
-    ("fetchTree",                FetchTree,                1),
-    ("__fetchurl",                 FetchUrl,                 1),
-    ("__filter",                   Filter,                   2),
-    ("__filterSource",             FilterSource,             2),
-    ("__findFile",                 FindFile,                 2),
-    ("__floor",                    Floor,                    1),
-    ("__foldl'",                   FoldlStrict,              3),
-    ("__fromJSON",                 FromJSON,                 1),
-    ("fromTOML",                 FromTOML,                 1),
-    ("__functionArgs",             FunctionArgs,             1),
-    ("__genList",                  GenList,                  2),
-    ("__genericClosure",           GenericClosure,           1),
-    ("__getAttr",                  GetAttr,                  2),
-    ("__getContext",               GetContext,               1),
-    ("__getEnv",                   GetEnv,                   1),
-    ("__groupBy",                  GroupBy,                  2),
-    ("__hasAttr",                  HasAttr,                  2),
-    ("__hasContext",               HasContext,               1),
-    ("__hashFile",                 HashFile,                 2),
-    ("__hashString",               HashString,               2),
-    ("__head",                     Head,                     1),
-    ("import",                   Import,                   1),
-    ("__intersectAttrs",           IntersectAttrs,           2),
-    ("__isAttrs",                  IsAttrs,                  1),
-    ("__isBool",                   IsBool,                   1),
-    ("__isFloat",                  IsFloat,                  1),
-    ("__isFunction",               IsFunction,               1),
-    ("__isInt",                    IsInt,                    1),
-    ("__isList",                   IsList,                   1),
-    ("isNull",                   IsNull,                   1),
-    ("__isPath",                   IsPath,                   1),
-    ("__isString",                 IsString,                 1),
-    ("__length",                   Length,                   1),
-    ("__lessThan",                 LessThan,                 2),
-    ("__listToAttrs",              ListToAttrs,              1),
-    ("map",                      Map,                      2),
-    ("__mapAttrs",                 MapAttrs,                 2),
-    ("__match",                    Match,                    2),
-    ("__mul",                      Mul,                      2),
-    ("null",                     Null,                     0), // constant, not a function
-    ("__parseDrvName",             ParseDrvName,             1),
-    ("__partition",                Partition,                2),
-    ("__path",                     Path,                     1),
-    ("__pathExists",               PathExists,               1),
-    ("placeholder",              Placeholder,              1),
-    ("__readDir",                  ReadDir,                  1),
-    ("__readFile",                 ReadFile,                 1),
-    ("__readFileType",             ReadFileType,             1),
-    ("removeAttrs",              RemoveAttrs,              2),
-    ("__replaceStrings",           ReplaceStrings,           3),
-    ("scopedImport",             ScopedImport,             2),
-    ("__seq",                      Seq,                      2),
-    ("__sort",                     Sort,                     2),
-    ("__split",                    Split,                    2),
-    ("__splitVersion",             SplitVersion,             1),
-    ("__storePath",                StorePath,                1),
-    ("__stringLength",             StringLength,             1),
-    ("__sub",                      Sub,                      2),
-    ("__substring",                Substring,                3),
-    ("__tail",                     Tail,                     1),
-    ("throw",                    Throw,                    1),
-    ("__toFile",                   ToFile,                   2),
-    ("__toJSON",                   ToJSON,                   1),
-    ("__toPath",                   ToPath,                   1),
-    ("toString",                 ToString,                 1),
-    ("__toXML",                    ToXML,                    1),
-    ("__trace",                    Trace,                    2),
-    ("__tryEval",                  TryEval,                  1),
-    ("__typeOf",                   TypeOf,                   1),
-    ("__unsafeDiscardStringContext", UnsafeDiscardStringContext, 1),
-    ("__unsafeGetAttrPos",         UnsafeGetAttrPos,         2),
-    ("__warn",                     Warn,                     2),
-    ("__zipAttrsWith",             ZipAttrsWith,             2),
-}
-
-/// Names that need to be pre-interned for builtin implementations.
-const EXTRA_INTERN_NAMES: &[&str] = &[
-    "builtins",
-    "currentSystem",
-    "langVersion",
-    "nixVersion",
-    "storeDir",
-    "nixPath",
-    "true",
-    "false",
-    // typeOf return values
-    "int",
-    "float",
-    "bool",
-    "string",
-    "path",
-    "null",
-    "set",
-    "list",
-    "lambda",
-    // attrset keys used by builtins
-    "name",
-    "value",
-    "success",
-    "right",
-    "wrong",
-    "key",
-    "operator",
-    "startSet",
-    "__toString",
-    "outPath",
-    "__functor",
-    "drvPath",
-    "type",
-    "derivation",
-    "version",
-];
-
-/// Returns true if this builtin has lazy argument semantics
-/// (not all args should be forced before dispatch).
-pub(super) fn is_lazy_builtin(id: BuiltinId) -> bool {
-    matches!(
-        id,
-        BuiltinId::Seq
-            | BuiltinId::DeepSeq
-            | BuiltinId::Trace
-            | BuiltinId::Warn
-            | BuiltinId::TryEval
-            | BuiltinId::AddErrorContext
-            | BuiltinId::Break
-    )
-}
-
-/// Intern all builtin names and extra names needed at runtime.
-fn intern_all_builtins(interner: &mut DefaultStringInterner) {
-    for &(name, _) in BUILTINS {
-        interner.get_or_intern(name);
-    }
-    for &name in EXTRA_INTERN_NAMES {
-        interner.get_or_intern(name);
-    }
-}
-
-pub(super) fn init_builtins<'gc>(
-    mc: &Mutation<'gc>,
-    strings: &mut DefaultStringInterner,
-) -> (
-    HashMap<StringId, Ir<'static, RawIrRef<'static>>>,
-    Value<'gc>,
-) {
-    let mut global_env = HashMap::new();
-    let builtins_sym = StringId(strings.get_or_intern("builtins"));
-    global_env.insert(builtins_sym, Ir::Builtins);
-    let mut entries = SmallVec::with_capacity(BUILTINS.len());
-
-    for (idx, &(name, arity)) in BUILTINS.iter().enumerate() {
-        let id = BuiltinId::try_from_primitive(idx as u8).expect("infallible");
-        if let Some(local_name) = name.strip_prefix("__") {
-            // scoped builtins
-            let name = StringId(strings.get_or_intern(name));
-            let local_name = StringId(strings.get_or_intern(local_name));
-            global_env.insert(name, Ir::Builtin(id));
-            entries.push((local_name, Value::new_inline(PrimOp { id, arity })));
-        } else {
-            // global builtins
-            let name = StringId(strings.get_or_intern(name));
-            global_env.insert(name, Ir::Builtin(id));
-            entries.push((name, Value::new_inline(PrimOp { id, arity })));
-        }
-    }
-
-    let consts = [
-        (
-            "__currentSystem",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("currentSystem"))),
-            // FIXME: detect currentSystem
-            Value::new_gc(Gc::new(mc, NixString::new("x86_64-linux"))),
-        ),
-        ("__langVersion", Ir::Int(6), Value::new_inline(6i32)),
-        (
-            "__nixVersion",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("nixVersion"))),
-            Value::new_gc(Gc::new(mc, NixString::new("2.24.0"))),
-        ),
-        (
-            "__storeDir",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("storeDir"))),
-            Value::new_gc(Gc::new(mc, NixString::new("/nix/store"))),
-        ),
-        (
-            "__nixPath",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("nixPath"))),
-            // FIXME: get from config
-            Value::new_gc(Gc::new(
-                mc,
-                List {
-                    inner: SmallVec::new(),
-                },
-            )),
-        ),
-        ("null", Ir::Null, Value::new_inline(Null)),
-        ("true", Ir::Bool(true), Value::new_inline(true)),
-        ("false", Ir::Bool(false), Value::new_inline(false)),
-    ];
-
-    for (idx, &(name, arity)) in BUILTINS.iter().enumerate() {
-        let id = BuiltinId::try_from_primitive(idx as u8).expect("infallible");
-        if let Some(local_name) = name.strip_prefix("__") {
-            // scoped builtins
-            let name = StringId(strings.get_or_intern(name));
-            let local_name = StringId(strings.get_or_intern(local_name));
-            global_env.insert(name, Ir::Builtin(id));
-            entries.push((local_name, Value::new_inline(PrimOp { id, arity })));
-        } else {
-            // global builtins
-            let name = StringId(strings.get_or_intern(name));
-            global_env.insert(name, Ir::Builtin(id));
-            entries.push((name, Value::new_inline(PrimOp { id, arity })));
-        }
-    }
-    for (name, ir, val) in consts {
-        if let Some(local_name) = name.strip_prefix("__") {
-            let name = StringId(strings.get_or_intern(name));
-            let local_name = StringId(strings.get_or_intern(local_name));
-            global_env.insert(name, ir);
-            entries.push((local_name, val));
-        } else {
-            let name = StringId(strings.get_or_intern(name));
-            global_env.insert(name, ir);
-            entries.push((name, val));
-        }
-    }
-
-    // Self-reference thunk for builtins.builtins
-    let self_ref_thunk: Gc<'gc, Thunk<'gc>> = Gc::new(mc, RefLock::new(ThunkState::Blackhole));
-    let sym = strings.get_or_intern("builtins");
-    entries.push((StringId(sym), Value::new_gc(self_ref_thunk)));
-
-    entries.sort_by_key(|(k, _)| *k);
-
-    let builtins_set = Gc::new(mc, unsafe { AttrSet::from_sorted_unchecked(entries) });
-    let builtins_val = Value::new_gc(builtins_set);
-
-    (global_env, builtins_val)
-}
-
-pub(super) type PrimOpArgs<'gc> = [Value<'gc>; 3];
-pub(super) type PrimOpStrictArgs<'gc> = [StrictValue<'gc>; 3];
-
-#[allow(non_snake_case)]
-pub(super) struct WellKnownSymbols {
-    abort: SymbolU32,
-    add: SymbolU32,
-    addErrorContext: SymbolU32,
-    all: SymbolU32,
-    any: SymbolU32,
-    appendContext: SymbolU32,
-    attrNames: SymbolU32,
-    attrValues: SymbolU32,
-    baseNameOf: SymbolU32,
-    bitAnd: SymbolU32,
-    bitOr: SymbolU32,
-    bitXor: SymbolU32,
-    catAttrs: SymbolU32,
-    ceil: SymbolU32,
-    compareVersions: SymbolU32,
-    concatLists: SymbolU32,
-    concatMap: SymbolU32,
-    concatStringsSep: SymbolU32,
-    convertHash: SymbolU32,
-    deepSeq: SymbolU32,
-    derivation: SymbolU32,
-    derivationStrict: SymbolU32,
-    dirOf: SymbolU32,
-    div: SymbolU32,
-    elem: SymbolU32,
-    elemAt: SymbolU32,
-    fetchGit: SymbolU32,
-    fetchMercurial: SymbolU32,
-    fetchTarball: SymbolU32,
-    fetchTree: SymbolU32,
-    fetchurl: SymbolU32,
-    filter: SymbolU32,
-    filterSource: SymbolU32,
-    findFile: SymbolU32,
-    floor: SymbolU32,
-    foldl: SymbolU32,
-    fromJSON: SymbolU32,
-    fromTOML: SymbolU32,
-    functionArgs: SymbolU32,
-    genList: SymbolU32,
-    genericClosure: SymbolU32,
-    getAttr: SymbolU32,
-    getContext: SymbolU32,
-    getEnv: SymbolU32,
-    groupBy: SymbolU32,
-    hasAttr: SymbolU32,
-    hasContext: SymbolU32,
-    hashFile: SymbolU32,
-    hashString: SymbolU32,
-    head: SymbolU32,
-    import: SymbolU32,
-    intersectAttrs: SymbolU32,
-    isAttrs: SymbolU32,
-    isBool: SymbolU32,
-    isFloat: SymbolU32,
-    isFunction: SymbolU32,
-    isInt: SymbolU32,
-    isList: SymbolU32,
-    isNull: SymbolU32,
-    isPath: SymbolU32,
-    isString: SymbolU32,
-    length: SymbolU32,
-    lessThan: SymbolU32,
-    listToAttrs: SymbolU32,
-    map: SymbolU32,
-    mapAttrs: SymbolU32,
-    match_: SymbolU32,
-    mul: SymbolU32,
-    null: SymbolU32,
-    parseDrvName: SymbolU32,
-    partition: SymbolU32,
-    path: SymbolU32,
-    pathExists: SymbolU32,
-    placeholder: SymbolU32,
-    readDir: SymbolU32,
-    readFile: SymbolU32,
-    readFileType: SymbolU32,
-    removeAttrs: SymbolU32,
-    replaceStrings: SymbolU32,
-    scopedImport: SymbolU32,
-    seq: SymbolU32,
-    sort: SymbolU32,
-    split: SymbolU32,
-    splitVersion: SymbolU32,
-    storePath: SymbolU32,
-    stringLength: SymbolU32,
-    sub: SymbolU32,
-    substring: SymbolU32,
-    tail: SymbolU32,
-    throw: SymbolU32,
-    toFile: SymbolU32,
-    toJSON: SymbolU32,
-    toPath: SymbolU32,
-    toString: SymbolU32,
-    toXML: SymbolU32,
-    trace: SymbolU32,
-    tryEval: SymbolU32,
-    typeOf: SymbolU32,
-    unsafeDiscardStringContext: SymbolU32,
-    unsafeGetAttrPos: SymbolU32,
-    warn: SymbolU32,
-    zipAttrsWith: SymbolU32,
-    break_: SymbolU32,
-}

fix/src/runtime/corepkgs/derivation.nix

@@ -1,31 +0,0 @@
-drvAttrs@{
-  outputs ? [ "out" ],
-  ...
-}:
-
-let
-
-  strict = derivationStrict drvAttrs;
-
-  commonAttrs =
-    drvAttrs
-    // (builtins.listToAttrs outputsList)
-    // {
-      all = map (x: x.value) outputsList;
-      inherit drvAttrs;
-    };
-
-  outputToAttrListElement = outputName: {
-    name = outputName;
-    value = commonAttrs // {
-      outPath = builtins.getAttr outputName strict;
-      drvPath = strict.drvPath;
-      type = "derivation";
-      inherit outputName;
-    };
-  };
-
-  outputsList = map outputToAttrListElement outputs;
-
-in
-(builtins.head outputsList).value

fix/src/runtime/corepkgs/fetchurl.nix

@@ -1,76 +0,0 @@
-{
-  system ? "", # obsolete
-  url,
-  hash ? "", # an SRI hash
-
-  # Legacy hash specification
-  md5 ? "",
-  sha1 ? "",
-  sha256 ? "",
-  sha512 ? "",
-  outputHash ?
-    if hash != "" then
-      hash
-    else if sha512 != "" then
-      sha512
-    else if sha1 != "" then
-      sha1
-    else if md5 != "" then
-      md5
-    else
-      sha256,
-  outputHashAlgo ?
-    if hash != "" then
-      ""
-    else if sha512 != "" then
-      "sha512"
-    else if sha1 != "" then
-      "sha1"
-    else if md5 != "" then
-      "md5"
-    else
-      "sha256",
-
-  executable ? false,
-  unpack ? false,
-  name ? baseNameOf (toString url),
-  # still translates to __impure to trigger derivationStrict error checks.
-  impure ? false,
-}:
-
-derivation (
-  {
-    builder = "builtin:fetchurl";
-
-    # New-style output content requirements.
-    outputHashMode = if unpack || executable then "recursive" else "flat";
-
-    inherit
-      name
-      url
-      executable
-      unpack
-      ;
-
-    system = "builtin";
-
-    # No need to double the amount of network traffic
-    preferLocalBuild = true;
-
-    impureEnvVars = [
-      # We borrow these environment variables from the caller to allow
-      # easy proxy configuration.  This is impure, but a fixed-output
-      # derivation like fetchurl is allowed to do so since its result is
-      # by definition pure.
-      "http_proxy"
-      "https_proxy"
-      "ftp_proxy"
-      "all_proxy"
-      "no_proxy"
-    ];
-
-    # To make "nix-prefetch-url" work.
-    urls = [ url ];
-  }
-  // (if impure then { __impure = true; } else { inherit outputHashAlgo outputHash; })
-)

fix/src/runtime/stack.rs

@@ -1,88 +0,0 @@
-use std::mem::MaybeUninit;
-
-use gc_arena::Collect;
-use smallvec::SmallVec;
-
-pub(super) struct Stack<const N: usize, T> {
-    inner: Box<[MaybeUninit<T>; N]>,
-    len: usize,
-}
-
-unsafe impl<'gc, const N: usize, T: Collect<'gc> + 'gc> Collect<'gc> for Stack<N, T> {
-    const NEEDS_TRACE: bool = T::NEEDS_TRACE;
-    fn trace<U: gc_arena::collect::Trace<'gc>>(&self, cc: &mut U) {
-        for item in self.inner[..self.len].iter() {
-            unsafe {
-                item.assume_init_ref().trace(cc);
-            }
-        }
-    }
-}
-
-impl<const N: usize, T> Default for Stack<N, T> {
-    fn default() -> Self {
-        Self::new()
-    }
-}
-
-impl<const N: usize, T> Stack<N, T> {
-    pub(super) fn new() -> Self {
-        Self {
-            inner: Box::new([const { MaybeUninit::uninit() }; N]),
-            len: 0,
-        }
-    }
-
-    pub(super) fn push(&mut self, val: T) -> Result<(), T> {
-        if self.len == N {
-            return Err(val);
-        }
-        unsafe {
-            self.inner.get_unchecked_mut(self.len).write(val);
-        }
-        self.len += 1;
-        Ok(())
-    }
-
-    pub(super) fn pop(&mut self) -> Option<T> {
-        if self.len == 0 {
-            return None;
-        }
-        let ret = unsafe {
-            self.inner
-                .get_unchecked_mut(self.len - 1)
-                .assume_init_read()
-        };
-        self.len -= 1;
-        Some(ret)
-    }
-
-    pub(super) fn tos(&self) -> Option<&T> {
-        if self.len == 0 {
-            return None;
-        }
-        Some(unsafe { self.inner.get_unchecked(self.len - 1).assume_init_ref() })
-    }
-
-    pub(super) fn tos_mut(&mut self) -> Option<&mut T> {
-        if self.len == 0 {
-            return None;
-        }
-        Some(unsafe { self.inner.get_unchecked_mut(self.len - 1).assume_init_mut() })
-    }
-
-    pub(super) fn len(&self) -> usize {
-        self.len
-    }
-
-    pub(super) fn pop_n<const M: usize>(&mut self, n: usize) -> SmallVec<[T; M]> {
-        assert!(n <= self.len, "pop_n: not enough items on stack");
-        let mut result = SmallVec::new();
-        let start = self.len - n;
-        for i in start..self.len {
-            result.push(unsafe { self.inner.get_unchecked(i).assume_init_read() });
-        }
-        self.len = start;
-        result
-    }
-}

fix/src/runtime/value.rs

@@ -1,609 +0,0 @@
-use std::fmt;
-use std::marker::PhantomData;
-use std::mem::size_of;
-use std::ops::Deref;
-
-use gc_arena::collect::Trace;
-use gc_arena::{Collect, Gc, Mutation, RefLock};
-use num_enum::TryFromPrimitive;
-use sealed::sealed;
-use smallvec::SmallVec;
-use string_interner::Symbol;
-use string_interner::symbol::SymbolU32;
-
-use crate::boxing::{RawBox, RawStore, RawTag, Value as RawValue};
-use crate::ir::StringId;
-use crate::runtime::builtins::BuiltinId;
-
-#[sealed]
-/// # Safety
-/// 1. TAG must be unique among all implementors.
-/// 2. TAG must be within 1..=7
-pub(crate) unsafe trait Storable {
-    const TAG: (bool, u8);
-}
-pub(crate) trait InlineStorable: Storable + RawStore {}
-pub(crate) trait GcStorable: Storable {}
-
-macro_rules! define_value_types {
-    (
-        inline { $($itype:ty => $itag:expr, $iname:literal;)* }
-        gc { $($gtype:ty => $gtag:expr, $gname:literal;)* }
-    ) => {
-        $(
-        #[sealed]
-        unsafe impl Storable for $itype {
-            const TAG: (bool, u8) = $itag;
-        }
-        impl InlineStorable for $itype {}
-        )*
-        $(
-        #[sealed]
-        unsafe impl Storable for $gtype {
-            const TAG: (bool, u8) = $gtag;
-        }
-        impl GcStorable for $gtype {}
-        )*
-
-        const _: () = assert!(size_of::<Value<'static>>() == 8);
-        $(const _: () = assert!(size_of::<$itype>() <= 6);)*
-        $(const _: () = { let (_, val) = $itag; assert!(val >= 1 && val <= 7); };)*
-        $(const _: () = { let (_, val) = $gtag; assert!(val >= 1 && val <= 7); };)*
-
-        const _: () = {
-            let tags: &[(bool, u8)] = &[$($itag),*, $($gtag),*];
-            let mut mask_false: u8 = 0;
-            let mut mask_true: u8 = 0;
-            let mut i = 0;
-            while i < tags.len() {
-                let (neg, val) = tags[i];
-                let bit = 1 << val;
-                if neg {
-                    assert!(mask_true & bit == 0, "duplicate true tag id");
-                    mask_true |= bit;
-                } else {
-                    assert!(mask_false & bit == 0, "duplicate false tag id");
-                    mask_false |= bit;
-                }
-                i += 1;
-            }
-        };
-
-        unsafe impl<'gc> Collect<'gc> for Value<'gc> {
-            const NEEDS_TRACE: bool = true;
-            fn trace<T: Trace<'gc>>(&self, cc: &mut T) {
-                let Some(tag) = self.raw.tag() else { return };
-                match tag.neg_val() {
-                    $(<$gtype as Storable>::TAG => unsafe {
-                        self.load_gc::<$gtype>().trace(cc)
-                    },)*
-                    $(<$itype as Storable>::TAG => (),)*
-                    (neg, val) => unreachable!("invalid tag: neg={neg}, val={val}"),
-                }
-            }
-        }
-
-        impl fmt::Debug for Value<'_> {
-            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                match self.tag() {
-                    None => write!(f, "Float({:?})", unsafe {
-                        self.raw.float().unwrap_unchecked()
-                    }),
-                    $(Some(<$itype as Storable>::TAG) => write!(f, "{}({:?})", $iname, unsafe {
-                        self.as_inline::<$itype>().unwrap_unchecked()
-                    }),)*
-                    $(Some(<$gtype as Storable>::TAG) =>
-                        write!(f, "{}(..)", $gname),)*
-                    Some((neg, val)) => write!(f, "Unknown(neg={neg}, val={val})"),
-                }
-            }
-        }
-
-        impl fmt::Debug for StaticValue {
-            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                match self.tag() {
-                    None => write!(f, "Float({:?})", unsafe {
-                        self.raw.float().unwrap_unchecked()
-                    }),
-                    $(Some(<$itype as Storable>::TAG) => write!(f, "{}({:?})", $iname, unsafe {
-                        self.as_inline::<$itype>().unwrap_unchecked()
-                    }),)*
-                    Some((neg, val)) => write!(f, "Unknown(neg={neg}, val={val})"),
-                }
-            }
-        }
-    };
-}
-
-define_value_types! {
-    inline {
-        i32 => (false, 1), "SmallInt";
-        bool => (false, 2), "Bool";
-        Null => (false, 3), "Null";
-        StringId => (false, 4), "SmallString";
-        PrimOp => (false, 5), "PrimOp";
-    }
-    gc {
-        i64 => (false, 6), "BigInt";
-        NixString => (false, 7), "String";
-        AttrSet<'_> => (true, 1), "AttrSet";
-        List<'_> => (true, 2), "List";
-        Thunk<'_> => (true, 3), "Thunk";
-        Closure<'_> => (true, 4), "Closure";
-        PrimOpApp<'_> => (true, 5), "PrimOpApp";
-    }
-}
-
-/// # Nix runtime value representation
-///
-/// NaN-boxed value fitting in 8 bytes.
-#[derive(Copy, Clone)]
-#[repr(transparent)]
-pub(crate) struct Value<'gc> {
-    raw: RawBox,
-    _marker: PhantomData<Gc<'gc, ()>>,
-}
-
-impl Default for Value<'_> {
-    #[inline(always)]
-    fn default() -> Self {
-        Self::new_inline(Null)
-    }
-}
-
-impl<'gc> Value<'gc> {
-    #[inline(always)]
-    fn from_raw_value(rv: RawValue) -> Self {
-        Self {
-            raw: RawBox::from_value(rv),
-            _marker: PhantomData,
-        }
-    }
-
-    /// Load a GC pointer from a value with a negative tag.
-    ///
-    /// # Safety
-    ///
-    /// The value must actually store a `Gc<'gc, T>` with the matching type.
-    #[inline(always)]
-    unsafe fn load_gc<T: GcStorable>(&self) -> Gc<'gc, T> {
-        unsafe {
-            let rv = self.raw.value().unwrap_unchecked();
-            let ptr: *const T = <*const T as RawStore>::from_val(rv);
-            Gc::from_ptr(ptr)
-        }
-    }
-
-    /// Returns the `(negative, val)` tag, or `None` for a float.
-    #[inline(always)]
-    fn tag(&self) -> Option<(bool, u8)> {
-        self.raw.tag().map(|t| t.neg_val())
-    }
-}
-
-impl<'gc> Value<'gc> {
-    #[inline]
-    pub(crate) fn new_float(val: f64) -> Self {
-        Self {
-            raw: RawBox::from_float(val),
-            _marker: PhantomData,
-        }
-    }
-
-    #[inline]
-    pub(crate) fn new_inline<T: InlineStorable>(val: T) -> Self {
-        Self::from_raw_value(RawValue::store(
-            unsafe { RawTag::new_unchecked(T::TAG.0, T::TAG.1) },
-            val,
-        ))
-    }
-
-    #[inline]
-    pub(crate) fn new_gc<T: GcStorable>(gc: Gc<'gc, T>) -> Self {
-        let ptr = Gc::as_ptr(gc);
-        Self::from_raw_value(RawValue::store(
-            unsafe { RawTag::new_unchecked(T::TAG.0, T::TAG.1) },
-            ptr,
-        ))
-    }
-
-    #[inline]
-    pub(crate) fn make_int(val: i64, mc: &Mutation<'gc>) -> Self {
-        if val >= i32::MIN as i64 && val <= i32::MAX as i64 {
-            Value::new_inline(val as i32)
-        } else {
-            Value::new_gc(Gc::new(mc, val))
-        }
-    }
-}
-
-impl<'gc> Value<'gc> {
-    #[inline]
-    pub(crate) fn is_float(&self) -> bool {
-        self.raw.is_float()
-    }
-
-    #[inline]
-    pub(crate) fn is<T: Storable>(&self) -> bool {
-        self.tag() == Some(T::TAG)
-    }
-}
-
-impl<'gc> Value<'gc> {
-    #[inline]
-    pub(crate) fn as_float(&self) -> Option<f64> {
-        self.raw.float().copied()
-    }
-
-    #[inline]
-    pub(crate) fn as_inline<T: InlineStorable>(&self) -> Option<T> {
-        if self.is::<T>() {
-            Some(unsafe {
-                let rv = self.raw.value().unwrap_unchecked();
-                T::from_val(rv)
-            })
-        } else {
-            None
-        }
-    }
-
-    #[inline]
-    pub(crate) fn as_gc<T: GcStorable>(&self) -> Option<Gc<'gc, T>> {
-        if self.is::<T>() {
-            Some(unsafe {
-                let rv = self.raw.value().unwrap_unchecked();
-                let ptr: *const T = <*const T as RawStore>::from_val(rv);
-                Gc::from_ptr(ptr)
-            })
-        } else {
-            None
-        }
-    }
-
-    #[inline]
-    pub(crate) fn restrict(self) -> Option<StrictValue<'gc>> {
-        if !self.is::<Thunk<'gc>>() {
-            Some(StrictValue(self))
-        } else {
-            None
-        }
-    }
-}
-
-#[derive(Copy, Clone)]
-#[repr(transparent)]
-pub(crate) struct StaticValue {
-    raw: RawBox,
-}
-
-impl Default for StaticValue {
-    #[inline(always)]
-    fn default() -> Self {
-        Self::new_inline(Null)
-    }
-}
-
-impl From<StaticValue> for Value<'_> {
-    #[inline]
-    fn from(value: StaticValue) -> Self {
-        Self {
-            raw: value.raw,
-            _marker: PhantomData,
-        }
-    }
-}
-
-impl StaticValue {
-    #[inline(always)]
-    fn from_raw_value(rv: RawValue) -> Self {
-        Self {
-            raw: RawBox::from_value(rv),
-        }
-    }
-
-    #[inline]
-    pub(crate) fn to_bits(self) -> u64 {
-        self.raw.to_bits()
-    }
-
-    #[inline]
-    pub(crate) fn new_float(val: f64) -> Self {
-        Self {
-            raw: RawBox::from_float(val),
-        }
-    }
-
-    #[inline]
-    pub(crate) fn new_inline<T: InlineStorable>(val: T) -> Self {
-        Self::from_raw_value(RawValue::store(
-            unsafe { RawTag::new_unchecked(T::TAG.0, T::TAG.1) },
-            val,
-        ))
-    }
-
-    #[inline]
-    pub(crate) fn is_float(&self) -> bool {
-        self.raw.is_float()
-    }
-
-    #[inline]
-    pub(crate) fn is<T: InlineStorable>(&self) -> bool {
-        self.tag() == Some(T::TAG)
-    }
-
-    #[inline]
-    pub(crate) fn as_float(&self) -> Option<f64> {
-        self.raw.float().copied()
-    }
-
-    #[inline]
-    pub(crate) fn as_inline<T: InlineStorable>(&self) -> Option<T> {
-        if self.is::<T>() {
-            Some(unsafe {
-                let rv = self.raw.value().unwrap_unchecked();
-                T::from_val(rv)
-            })
-        } else {
-            None
-        }
-    }
-
-    /// Returns the `(negative, val)` tag, or `None` for a float.
-    #[inline(always)]
-    fn tag(&self) -> Option<(bool, u8)> {
-        self.raw.tag().map(|t| t.neg_val())
-    }
-}
-
-#[derive(Clone, Copy, Debug)]
-pub(crate) struct Null;
-impl RawStore for Null {
-    fn to_val(self, value: &mut RawValue) {
-        value.set_data([0; 6]);
-    }
-    fn from_val(_: &RawValue) -> Self {
-        Self
-    }
-}
-
-impl RawStore for StringId {
-    fn to_val(self, value: &mut RawValue) {
-        (self.0.to_usize() as u32).to_val(value);
-    }
-    fn from_val(value: &RawValue) -> Self {
-        Self(
-            SymbolU32::try_from_usize(u32::from_val(value) as usize)
-                .expect("failed to read StringId from Value"),
-        )
-    }
-}
-
-/// Heap-allocated Nix string.
-///
-/// Stored on the GC heap via `Gc<'gc, NixString>`. The string data itself
-/// lives in a standard `Box<str>` owned by this struct; the GC only manages
-/// the outer allocation.
-#[derive(Collect)]
-#[collect(require_static)]
-pub(crate) struct NixString {
-    data: Box<str>,
-    // TODO: string context for derivation dependency tracking
-}
-
-impl NixString {
-    pub(crate) fn new(s: impl Into<Box<str>>) -> Self {
-        Self { data: s.into() }
-    }
-
-    pub(crate) fn as_str(&self) -> &str {
-        &self.data
-    }
-}
-
-impl fmt::Debug for NixString {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Debug::fmt(&self.data, f)
-    }
-}
-
-#[derive(Collect, Debug, Default)]
-#[collect(no_drop)]
-pub(crate) struct AttrSet<'gc> {
-    entries: SmallVec<[(StringId, Value<'gc>); 4]>,
-}
-
-impl<'gc> Deref for AttrSet<'gc> {
-    type Target = [(StringId, Value<'gc>)];
-    fn deref(&self) -> &Self::Target {
-        &self.entries
-    }
-}
-
-impl<'gc> AttrSet<'gc> {
-    pub(crate) unsafe fn from_sorted_unchecked(
-        entries: SmallVec<[(StringId, Value<'gc>); 4]>,
-    ) -> Self {
-        debug_assert!(entries.is_sorted_by_key(|(key, _)| *key));
-        Self { entries }
-    }
-
-    pub(crate) fn lookup(&self, key: StringId) -> Option<Value<'gc>> {
-        self.entries
-            .binary_search_by_key(&key, |(k, _)| *k)
-            .ok()
-            .map(|i| self.entries[i].1)
-    }
-
-    pub(crate) fn has(&self, key: StringId) -> bool {
-        self.entries.binary_search_by_key(&key, |(k, _)| *k).is_ok()
-    }
-
-    pub(crate) fn merge(&self, other: &Self, mc: &Mutation<'gc>) -> Gc<'gc, Self> {
-        use std::cmp::Ordering::*;
-
-        debug_assert!(self.entries.is_sorted_by_key(|(key, _)| *key));
-        debug_assert!(other.entries.is_sorted_by_key(|(key, _)| *key));
-
-        let mut entries = SmallVec::new();
-        let mut i = 0;
-        let mut j = 0;
-        while i < self.entries.len() && j < other.entries.len() {
-            match self.entries[i].0.cmp(&other.entries[j].0) {
-                Less => {
-                    entries.push(self.entries[i]);
-                    i += 1;
-                }
-                Greater => {
-                    entries.push(other.entries[j]);
-                    j += 1;
-                }
-                Equal => {
-                    entries.push(other.entries[j]);
-                    i += 1;
-                    j += 1;
-                }
-            }
-        }
-        entries.extend(other.entries[j..].iter().cloned());
-        entries.extend(self.entries[i..].iter().cloned());
-
-        debug_assert!(entries.is_sorted_by_key(|(key, _)| *key));
-
-        Gc::new(mc, AttrSet { entries })
-    }
-}
-
-#[derive(Collect, Debug, Default)]
-#[collect(no_drop)]
-pub(crate) struct List<'gc> {
-    pub(crate) inner: SmallVec<[Value<'gc>; 4]>,
-}
-impl<'gc> Deref for List<'gc> {
-    type Target = SmallVec<[Value<'gc>; 4]>;
-    fn deref(&self) -> &Self::Target {
-        &self.inner
-    }
-}
-
-pub(crate) type Thunk<'gc> = RefLock<ThunkState<'gc>>;
-
-#[derive(Collect, Debug)]
-#[collect(no_drop)]
-pub(crate) enum ThunkState<'gc> {
-    Pending {
-        ip: usize,
-        env: Gc<'gc, RefLock<Env<'gc>>>,
-    },
-    Apply {
-        func: Value<'gc>,
-        arg: Value<'gc>,
-    },
-    Blackhole,
-    Evaluated(Value<'gc>),
-}
-
-#[derive(Collect, Debug)]
-#[collect(no_drop)]
-pub(crate) struct Env<'gc> {
-    pub(crate) locals: SmallVec<[Value<'gc>; 4]>,
-    pub(crate) prev: Option<Gc<'gc, RefLock<Env<'gc>>>>,
-}
-
-impl<'gc> Env<'gc> {
-    pub(crate) fn empty() -> Self {
-        Env {
-            locals: SmallVec::new(),
-            prev: None,
-        }
-    }
-
-    pub(crate) fn with_arg(
-        arg: Value<'gc>,
-        n_locals: u32,
-        prev: Gc<'gc, RefLock<Env<'gc>>>,
-    ) -> Self {
-        let mut locals = smallvec::smallvec![Value::default(); 1 + n_locals as usize];
-        locals[0] = arg;
-        Env {
-            locals,
-            prev: Some(prev),
-        }
-    }
-}
-
-#[derive(Collect, Debug)]
-#[collect(no_drop)]
-pub(crate) struct Closure<'gc> {
-    pub(crate) ip: u32,
-    pub(crate) n_locals: u32,
-    pub(crate) env: Gc<'gc, RefLock<Env<'gc>>>,
-    pub(crate) pattern: Option<Gc<'gc, PatternInfo>>,
-}
-
-#[derive(Collect, Debug)]
-#[collect(require_static)]
-pub(crate) struct PatternInfo {
-    pub(crate) required: SmallVec<[StringId; 4]>,
-    pub(crate) optional: SmallVec<[StringId; 4]>,
-    pub(crate) ellipsis: bool,
-    pub(crate) param_spans: Box<[(StringId, u32)]>,
-}
-
-#[derive(Clone, Copy, Debug, Collect)]
-#[collect(require_static)]
-pub(crate) struct PrimOp {
-    pub(crate) id: BuiltinId,
-    pub(crate) arity: u8,
-}
-
-impl RawStore for PrimOp {
-    fn to_val(self, value: &mut RawValue) {
-        value.set_data([0, 0, 0, 0, self.id as u8, self.arity]);
-    }
-    fn from_val(value: &RawValue) -> Self {
-        let [.., id, arity] = *value.data();
-        Self {
-            id: BuiltinId::try_from_primitive(id).expect("invalid BuiltinId"),
-            arity,
-        }
-    }
-}
-
-#[derive(Collect, Debug)]
-#[collect(no_drop)]
-pub(crate) struct PrimOpApp<'gc> {
-    pub(crate) primop: PrimOp,
-    pub(crate) args: SmallVec<[Value<'gc>; 2]>,
-}
-
-#[derive(Copy, Clone, Default)]
-#[repr(transparent)]
-pub(crate) struct StrictValue<'gc>(Value<'gc>);
-
-impl<'gc> StrictValue<'gc> {
-    #[inline]
-    pub(crate) fn relax(self) -> Value<'gc> {
-        self.0
-    }
-}
-
-impl<'gc> Deref for StrictValue<'gc> {
-    type Target = Value<'gc>;
-    #[inline]
-    fn deref(&self) -> &Value<'gc> {
-        &self.0
-    }
-}
-
-impl fmt::Debug for StrictValue<'_> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Debug::fmt(&self.0, f)
-    }
-}
-
-unsafe impl<'gc> Collect<'gc> for StrictValue<'gc> {
-    const NEEDS_TRACE: bool = true;
-    fn trace<T: gc_arena::collect::Trace<'gc>>(&self, cc: &mut T) {
-        self.0.trace(cc);
-    }
-}

fix/src/string_context.rs

@@ -1,209 +0,0 @@
-use std::collections::{BTreeMap, BTreeSet, VecDeque};
-
-pub enum StringContextElem {
-    Opaque { path: String },
-    DrvDeep { drv_path: String },
-    Built { drv_path: String, output: String },
-}
-
-impl StringContextElem {
-    pub fn decode(encoded: &str) -> Self {
-        if let Some(drv_path) = encoded.strip_prefix('=') {
-            StringContextElem::DrvDeep {
-                drv_path: drv_path.to_string(),
-            }
-        } else if let Some(rest) = encoded.strip_prefix('!') {
-            if let Some(second_bang) = rest.find('!') {
-                let output = rest[..second_bang].to_string();
-                let drv_path = rest[second_bang + 1..].to_string();
-                StringContextElem::Built { drv_path, output }
-            } else {
-                StringContextElem::Opaque {
-                    path: encoded.to_string(),
-                }
-            }
-        } else {
-            StringContextElem::Opaque {
-                path: encoded.to_string(),
-            }
-        }
-    }
-}
-
-pub type InputDrvs = BTreeMap<String, BTreeSet<String>>;
-pub type Srcs = BTreeSet<String>;
-pub fn extract_input_drvs_and_srcs(context: &[String]) -> Result<(InputDrvs, Srcs), String> {
-    let mut input_drvs: BTreeMap<String, BTreeSet<String>> = BTreeMap::new();
-    let mut input_srcs: BTreeSet<String> = BTreeSet::new();
-
-    for encoded in context {
-        match StringContextElem::decode(encoded) {
-            StringContextElem::Opaque { path } => {
-                input_srcs.insert(path);
-            }
-            StringContextElem::DrvDeep { drv_path } => {
-                compute_fs_closure(&drv_path, &mut input_drvs, &mut input_srcs)?;
-            }
-            StringContextElem::Built { drv_path, output } => {
-                input_drvs.entry(drv_path).or_default().insert(output);
-            }
-        }
-    }
-
-    Ok((input_drvs, input_srcs))
-}
-
-fn compute_fs_closure(
-    drv_path: &str,
-    input_drvs: &mut BTreeMap<String, BTreeSet<String>>,
-    input_srcs: &mut BTreeSet<String>,
-) -> Result<(), String> {
-    let mut queue: VecDeque<String> = VecDeque::new();
-    let mut visited: BTreeSet<String> = BTreeSet::new();
-
-    queue.push_back(drv_path.to_string());
-
-    while let Some(current_path) = queue.pop_front() {
-        if visited.contains(&current_path) {
-            continue;
-        }
-        visited.insert(current_path.clone());
-        input_srcs.insert(current_path.clone());
-
-        if !current_path.ends_with(".drv") {
-            continue;
-        }
-
-        let content = std::fs::read_to_string(&current_path)
-            .map_err(|e| format!("failed to read derivation {}: {}", current_path, e))?;
-
-        let inputs = parse_derivation_inputs(&content)
-            .ok_or_else(|| format!("failed to parse derivation {}", current_path))?;
-
-        for src in inputs.input_srcs {
-            input_srcs.insert(src.clone());
-            if !visited.contains(&src) {
-                queue.push_back(src);
-            }
-        }
-
-        for (dep_drv, outputs) in inputs.input_drvs {
-            input_srcs.insert(dep_drv.clone());
-            let entry = input_drvs.entry(dep_drv.clone()).or_default();
-            for output in outputs {
-                entry.insert(output);
-            }
-            if !visited.contains(&dep_drv) {
-                queue.push_back(dep_drv);
-            }
-        }
-    }
-
-    Ok(())
-}
-
-struct DerivationInputs {
-    input_drvs: Vec<(String, Vec<String>)>,
-    input_srcs: Vec<String>,
-}
-
-fn parse_derivation_inputs(aterm: &str) -> Option<DerivationInputs> {
-    let aterm = aterm.strip_prefix("Derive([")?;
-
-    let mut bracket_count: i32 = 1;
-    let mut pos = 0;
-    let bytes = aterm.as_bytes();
-    while pos < bytes.len() && bracket_count > 0 {
-        match bytes[pos] {
-            b'[' => bracket_count += 1,
-            b']' => bracket_count -= 1,
-            _ => {}
-        }
-        pos += 1;
-    }
-    if bracket_count != 0 {
-        return None;
-    }
-
-    let rest = &aterm[pos..];
-    let rest = rest.strip_prefix(",[")?;
-
-    let mut input_drvs = Vec::new();
-    let mut bracket_count: i32 = 1;
-    let mut start = 0;
-    pos = 0;
-    let bytes = rest.as_bytes();
-
-    while pos < bytes.len() && bracket_count > 0 {
-        match bytes[pos] {
-            b'[' => bracket_count += 1,
-            b']' => bracket_count -= 1,
-            b'(' if bracket_count == 1 => {
-                start = pos;
-            }
-            b')' if bracket_count == 1 => {
-                let entry = &rest[start + 1..pos];
-                if let Some((drv_path, outputs)) = parse_input_drv_entry(entry) {
-                    input_drvs.push((drv_path, outputs));
-                }
-            }
-            _ => {}
-        }
-        pos += 1;
-    }
-
-    let rest = &rest[pos..];
-    let rest = rest.strip_prefix(",[")?;
-
-    let mut input_srcs = Vec::new();
-    bracket_count = 1;
-    pos = 0;
-    let bytes = rest.as_bytes();
-
-    while pos < bytes.len() && bracket_count > 0 {
-        match bytes[pos] {
-            b'[' => bracket_count += 1,
-            b']' => bracket_count -= 1,
-            b'"' if bracket_count == 1 => {
-                pos += 1;
-                let src_start = pos;
-                while pos < bytes.len() && bytes[pos] != b'"' {
-                    if bytes[pos] == b'\\' && pos + 1 < bytes.len() {
-                        pos += 2;
-                    } else {
-                        pos += 1;
-                    }
-                }
-                let src = std::str::from_utf8(&bytes[src_start..pos]).ok()?;
-                input_srcs.push(src.to_string());
-            }
-            _ => {}
-        }
-        pos += 1;
-    }
-
-    Some(DerivationInputs {
-        input_drvs,
-        input_srcs,
-    })
-}
-
-fn parse_input_drv_entry(entry: &str) -> Option<(String, Vec<String>)> {
-    let entry = entry.strip_prefix('"')?;
-    let quote_end = entry.find('"')?;
-    let drv_path = entry[..quote_end].to_string();
-
-    let rest = &entry[quote_end + 1..];
-    let rest = rest.strip_prefix(",[")?;
-    let rest = rest.strip_suffix(']')?;
-
-    let mut outputs = Vec::new();
-    for part in rest.split(',') {
-        let part = part.trim();
-        if let Some(name) = part.strip_prefix('"').and_then(|s| s.strip_suffix('"')) {
-            outputs.push(name.to_string());
-        }
-    }
-
-    Some((drv_path, outputs))
-}

fix/tests/tests/derivation.rs

@@ -1,4 +1,4 @@
-use fix::value::Value;
+use fix_lang::Value;
 
 use crate::utils::{eval_deep, eval_deep_result};
 

fix/tests/tests/io_operations.rs

@@ -1,6 +1,6 @@
-use fix::error::Source;
+use fix::Evaluator;
-use fix::runtime::Runtime;
+use fix_error::Source;
-use fix::value::Value;
+use fix_lang::Value;
 
 use crate::utils::{eval, eval_result};
 
@@ -97,7 +97,7 @@ fn import_with_complex_dependency_graph() {
 
 #[test_log::test]
 fn path_with_file() {
-    let mut ctx = Runtime::new().unwrap();
+    let mut ctx = Evaluator::new();
     let temp_dir = tempfile::tempdir().unwrap();
     let test_file = temp_dir.path().join("test.txt");
     std::fs::write(&test_file, "Hello, World!").unwrap();
@@ -136,7 +136,7 @@ fn path_with_custom_name() {
 
 #[test_log::test]
 fn path_with_directory_recursive() {
-    let mut ctx = Runtime::new().unwrap();
+    let mut ctx = Evaluator::new();
     let temp_dir = tempfile::tempdir().unwrap();
     let test_dir = temp_dir.path().join("mydir");
     std::fs::create_dir_all(&test_dir).unwrap();
@@ -159,7 +159,7 @@ fn path_with_directory_recursive() {
 
 #[test_log::test]
 fn path_flat_with_file() {
-    let mut ctx = Runtime::new().unwrap();
+    let mut ctx = Evaluator::new();
     let temp_dir = tempfile::tempdir().unwrap();
     let test_file = temp_dir.path().join("flat.txt");
     std::fs::write(&test_file, "Flat content").unwrap();

fix/tests/tests/lang.rs

@@ -2,9 +2,9 @@
 
 use std::path::PathBuf;
 
-use fix::error::Source;
+use fix::Evaluator;
-use fix::runtime::Runtime;
+use fix_error::{Source, SourceType};
-use fix::value::Value;
+use fix_lang::Value;
 
 fn get_lang_dir() -> PathBuf {
     PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("tests/tests/lang")
@@ -14,10 +14,10 @@ fn eval_file(name: &str) -> Result<(Value, Source), String> {
     let lang_dir = get_lang_dir();
     let nix_path = lang_dir.join(format!("{name}.nix"));
 
-    let mut ctx = Runtime::new().map_err(|e| e.to_string())?;
+    let mut ctx = Evaluator::new();
     let content = std::fs::read_to_string(&nix_path).unwrap();
     let source = Source {
-        ty: fix::error::SourceType::File(nix_path.into()),
+        ty: SourceType::File(nix_path.into()),
         src: content.into(),
     };
     ctx.eval_deep(source.clone())

fix/tests/tests/string_context.rs

@@ -1,5 +1,5 @@
-use fix::runtime::Runtime;
+use fix::Evaluator;
-use fix::value::Value;
+use fix_lang::Value;
 
 use crate::utils::eval_result;
 
@@ -153,7 +153,7 @@ fn string_add_merges_context() {
 
 #[test_log::test]
 fn context_in_derivation_args() {
-    let mut rt = Runtime::new().unwrap();
+    let mut rt = Evaluator::new();
     let result = rt
         .eval(
             r#"
@@ -182,7 +182,7 @@ fn context_in_derivation_args() {
 
 #[test_log::test]
 fn context_in_derivation_env() {
-    let mut rt = Runtime::new().unwrap();
+    let mut rt = Evaluator::new();
     let result = rt
         .eval(
             r#"
@@ -224,7 +224,7 @@ fn tostring_preserves_context() {
 
 #[test_log::test]
 fn interpolation_derivation_returns_outpath() {
-    let mut rt = Runtime::new().unwrap();
+    let mut rt = Evaluator::new();
     let result = rt
         .eval(
             r#"

fix/tests/tests/utils.rs

@@ -1,38 +1,31 @@
 #![allow(dead_code)]
 
-use fix::error::{Result, Source};
+use fix::Evaluator;
-use fix::runtime::Runtime;
+use fix_error::{Result, Source};
-use fix::value::Value;
+use fix_lang::Value;
 
 pub fn eval(expr: &str) -> Value {
-    Runtime::new()
+    Evaluator::new()
-        .unwrap()
         .eval(Source::new_eval(expr.into()).unwrap())
         .unwrap()
 }
 
 pub fn eval_shallow(expr: &str) -> Value {
-    Runtime::new()
+    Evaluator::new()
-        .unwrap()
         .eval_shallow(Source::new_eval(expr.into()).unwrap())
         .unwrap()
 }
 
 pub fn eval_deep(expr: &str) -> Value {
-    Runtime::new()
+    Evaluator::new()
-        .unwrap()
         .eval_deep(Source::new_eval(expr.into()).unwrap())
         .unwrap()
 }
 
 pub fn eval_deep_result(expr: &str) -> Result<Value> {
-    Runtime::new()
+    Evaluator::new().eval_deep(Source::new_eval(expr.into()).unwrap())
-        .unwrap()
-        .eval_deep(Source::new_eval(expr.into()).unwrap())
 }
 
 pub fn eval_result(expr: &str) -> Result<Value> {
-    Runtime::new()
+    Evaluator::new().eval(Source::new_eval(expr.into()).unwrap())
-        .unwrap()
-        .eval(Source::new_eval(expr.into()).unwrap())
 }

flake.lock

@@ -1,5 +1,63 @@
 {
   "nodes": {
+    "blueprint": {
+      "inputs": {
+        "nixpkgs": [
+          "llm-agents",
+          "nixpkgs"
+        ],
+        "systems": [
+          "llm-agents",
+          "systems"
+        ]
+      },
+      "locked": {
+        "lastModified": 1776249299,
+        "narHash": "sha256-Dt9t1TGRmJFc0xVYhttNBD6QsAgHOHCArqGa0AyjrJY=",
+        "owner": "numtide",
+        "repo": "blueprint",
+        "rev": "56131e8628f173d24a27f6d27c0215eff57e40dd",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "blueprint",
+        "type": "github"
+      }
+    },
+    "bun2nix": {
+      "inputs": {
+        "flake-parts": [
+          "llm-agents",
+          "flake-parts"
+        ],
+        "nixpkgs": [
+          "llm-agents",
+          "nixpkgs"
+        ],
+        "systems": [
+          "llm-agents",
+          "systems"
+        ],
+        "treefmt-nix": [
+          "llm-agents",
+          "treefmt-nix"
+        ]
+      },
+      "locked": {
+        "lastModified": 1778446047,
+        "narHash": "sha256-oQvcadh2BCkrog+SGrG6YffKJrveYpjj3TdQJWaKhaM=",
+        "owner": "nix-community",
+        "repo": "bun2nix",
+        "rev": "f2bc12af1a6369648aac41041ceeaa0b866599c6",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "bun2nix",
+        "type": "github"
+      }
+    },
     "fenix": {
       "inputs": {
         "nixpkgs": [
@@ -8,11 +66,11 @@
         "rust-analyzer-src": "rust-analyzer-src"
       },
       "locked": {
-        "lastModified": 1774596377,
+        "lastModified": 1781343250,
-        "narHash": "sha256-DiSLMxyTwIUAlhOe34r6kKNQRv6PTF+vf0MG45mAyn4=",
+        "narHash": "sha256-KBJktAwDG9+10j2wMfvOVkBEhZr3yS769xoqqdFI62s=",
         "owner": "nix-community",
         "repo": "fenix",
-        "rev": "a88a1c8cf2f094da6347fcec54089f4bcb518409",
+        "rev": "aad7d8bb6936d473c2b9d1a5846a1fe1bc92767a",
         "type": "github"
       },
       "original": {
@@ -24,24 +82,70 @@
     "flake-compat": {
       "flake": false,
       "locked": {
-        "lastModified": 1751685974,
+        "lastModified": 1777699697,
-        "narHash": "sha256-NKw96t+BgHIYzHUjkTK95FqYRVKB8DHpVhefWSz/kTw=",
+        "narHash": "sha256-Eg9b/rq/ECYwNwEXs5i9wHyhxNI0JrYx2srdI2uZMaQ=",
-        "rev": "549f2762aebeff29a2e5ece7a7dc0f955281a1d1",
+        "rev": "382052b74656a369c5408822af3f2501e9b1af81",
         "type": "tarball",
-        "url": "https://git.lix.systems/api/v1/repos/lix-project/flake-compat/archive/549f2762aebeff29a2e5ece7a7dc0f955281a1d1.tar.gz"
+        "url": "https://git.lix.systems/api/v1/repos/lix-project/flake-compat/archive/382052b74656a369c5408822af3f2501e9b1af81.tar.gz"
       },
       "original": {
         "type": "tarball",
         "url": "https://git.lix.systems/lix-project/flake-compat/archive/main.tar.gz"
       }
     },
+    "flake-parts": {
+      "inputs": {
+        "nixpkgs-lib": [
+          "llm-agents",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1778716662,
+        "narHash": "sha256-m1Yf0wZ8j1OHjTc2UwHwyQRSnNeSgLJOd7q5Y45hzi4=",
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "rev": "f7c1a2d347e4c52d5fb8d10cb4d94b5884e546fb",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "flake-parts",
+        "type": "github"
+      }
+    },
+    "llm-agents": {
+      "inputs": {
+        "blueprint": "blueprint",
+        "bun2nix": "bun2nix",
+        "flake-parts": "flake-parts",
+        "nixpkgs": [
+          "nixpkgs"
+        ],
+        "systems": "systems",
+        "treefmt-nix": "treefmt-nix"
+      },
+      "locked": {
+        "lastModified": 1781330261,
+        "narHash": "sha256-2fFAGel2VVXr5mwrTXldqXva2ng3T3HHxyuBKRIxauI=",
+        "owner": "numtide",
+        "repo": "llm-agents.nix",
+        "rev": "24ec6b7b1ddf8896ac8df3b65dc564575e0a1928",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "llm-agents.nix",
+        "type": "github"
+      }
+    },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1774386573,
+        "lastModified": 1781074563,
-        "narHash": "sha256-4hAV26quOxdC6iyG7kYaZcM3VOskcPUrdCQd/nx8obc=",
+        "narHash": "sha256-md8WlXOlfnIeHeOScMTTHFyf2d6iaTwPl2apR5EQ3P4=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "46db2e09e1d3f113a13c0d7b81e2f221c63b8ce9",
+        "rev": "9ae611a455b90cf061d8f332b977e387bda8e1ca",
         "type": "github"
       },
       "original": {
@@ -55,17 +159,18 @@
       "inputs": {
         "fenix": "fenix",
         "flake-compat": "flake-compat",
+        "llm-agents": "llm-agents",
         "nixpkgs": "nixpkgs"
       }
     },
     "rust-analyzer-src": {
       "flake": false,
       "locked": {
-        "lastModified": 1774569884,
+        "lastModified": 1781294997,
-        "narHash": "sha256-E8iWEPzg7OnE0XXXjo75CX7xFauqzJuGZ5wSO9KS8Ek=",
+        "narHash": "sha256-XjCyIvJw4JtcwItTKRdQz5h1pLF9hr8ZSYeMP+/1d3A=",
         "owner": "rust-lang",
         "repo": "rust-analyzer",
-        "rev": "443ddcddd0c73b07b799d052f5ef3b448c2f3508",
+        "rev": "3f92cd1612268995d5667bd04fa03ba2916413d9",
         "type": "github"
       },
       "original": {
@@ -74,6 +179,42 @@
         "repo": "rust-analyzer",
         "type": "github"
       }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "llm-agents",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1780220602,
+        "narHash": "sha256-eynAfOmbmxJnkp7YewvCEbShNnnYJ9gLLqkzsYtBPeM=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "db947814a175b7ca6ded66e21383d938df01c227",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",

flake.nix

@@ -3,18 +3,30 @@
     nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
     fenix.url = "github:nix-community/fenix";
     fenix.inputs.nixpkgs.follows = "nixpkgs";
+    llm-agents = {
+      url = "github:numtide/llm-agents.nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
     flake-compat = {
       url = "https://git.lix.systems/lix-project/flake-compat/archive/main.tar.gz";
       flake = false;
     };
   };
-  outputs = { nixpkgs, fenix, ... }:
+  outputs =
+    inputs@{ nixpkgs, fenix, ... }:
     let
       forAllSystems = nixpkgs.lib.genAttrs nixpkgs.lib.systems.flakeExposed;
     in
     {
-      devShells = forAllSystems (system:
+      devShells = forAllSystems (
-        let pkgs = import nixpkgs { inherit system; config.allowUnfree = true; }; in
+        system:
+        let
+          pkgs = import nixpkgs {
+            inherit system;
+            config.allowUnfree = true;
+          };
+          llm-agents = inputs.llm-agents.packages.${pkgs.stdenv.hostPlatform.system};
+        in
         {
           default = pkgs.mkShell {
             packages = with pkgs; [
@@ -26,23 +38,21 @@
                 "rustfmt"
                 "rust-analyzer"
               ])
-              cargo-outdated
               cargo-machete
+              cargo-bloat
               lldb
               valgrind
+              kdePackages.kcachegrind
               hyperfine
               just
               samply
-              jq
               tokei
+              tombi
 
-              nodejs
+              # llm-agents.codex
-              nodePackages.npm
+              llm-agents.claude-code
-              biome
+              llm-agents.opencode
-
+              # llm-agents.forge
-              claude-code
-              codex
-              opencode
             ];
           };
         }

typos.toml

@@ -1,7 +1,7 @@
 [files]
 extend-exclude = [
-    "nix-js/tests/tests/regex.rs",
+  "nix-js/tests/tests/regex.rs",
-    "nix-js/tests/tests/lang",
+  "nix-js/tests/tests/lang",
 ]
 
 [default.extend-words]