STW

.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.lock

@@ -449,6 +449,8 @@ dependencies = [
  "clap",
  "criterion",
  "ere",
+ "fix-abstract-vm",
+ "fix-builtins",
  "fix-codegen",
  "fix-common",
  "fix-error",
@@ -468,6 +470,23 @@ dependencies = [
  "tracing-subscriber",
 ]
 
+[[package]]
+name = "fix-abstract-vm"
+version = "0.1.0"
+dependencies = [
+ "fix-builtins",
+ "fix-codegen",
+ "fix-common",
+ "fix-error",
+ "gc-arena",
+ "hashbrown 0.16.1",
+ "likely_stable",
+ "num_enum",
+ "smallvec",
+ "sptr",
+ "string-interner",
+]
+
 [[package]]
 name = "fix-builtins"
 version = "0.1.0"
@@ -525,20 +544,39 @@ dependencies = [
 ]
 
 [[package]]
-name = "fix-vm"
+name = "fix-primops"
 version = "0.1.0"
 dependencies = [
+ "fix-abstract-vm",
  "fix-builtins",
  "fix-codegen",
  "fix-common",
  "fix-error",
  "gc-arena",
  "hashbrown 0.16.1",
+ "num_enum",
+ "smallvec",
+ "string-interner",
+]
+
+[[package]]
+name = "fix-vm"
+version = "0.1.0"
+dependencies = [
+ "fix-abstract-vm",
+ "fix-builtins",
+ "fix-codegen",
+ "fix-common",
+ "fix-error",
+ "fix-primops",
+ "gc-arena",
+ "hashbrown 0.16.1",
  "likely_stable",
  "num_enum",
  "smallvec",
  "sptr",
  "string-interner",
+ "sysinfo",
 ]
 
 [[package]]
@@ -840,6 +878,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "ntapi"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3b335231dfd352ffb0f8017f3b6027a4917f7df785ea2143d8af2adc66980ae"
+dependencies = [
+ "winapi",
+]
+
 [[package]]
 name = "nu-ansi-term"
 version = "0.50.3"
@@ -880,6 +927,25 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "objc2-core-foundation"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2a180dd8642fa45cdb7dd721cd4c11b1cadd4929ce112ebd8b9f5803cc79d536"
+dependencies = [
+ "bitflags",
+]
+
+[[package]]
+name = "objc2-io-kit"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "33fafba39597d6dc1fb709123dfa8289d39406734be322956a69f0931c73bb15"
+dependencies = [
+ "libc",
+ "objc2-core-foundation",
+]
+
 [[package]]
 name = "object"
 version = "0.37.3"
@@ -1285,6 +1351,20 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "sysinfo"
+version = "0.38.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "92ab6a2f8bfe508deb3c6406578252e491d299cbbf3bc0529ecc3313aee4a52f"
+dependencies = [
+ "libc",
+ "memchr",
+ "ntapi",
+ "objc2-core-foundation",
+ "objc2-io-kit",
+ "windows",
+]
+
 [[package]]
 name = "tempfile"
 version = "3.27.0"
@@ -1678,12 +1758,107 @@ version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
 
+[[package]]
+name = "windows"
+version = "0.62.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "527fadee13e0c05939a6a05d5bd6eec6cd2e3dbd648b9f8e447c6518133d8580"
+dependencies = [
+ "windows-collections",
+ "windows-core",
+ "windows-future",
+ "windows-numerics",
+]
+
+[[package]]
+name = "windows-collections"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "23b2d95af1a8a14a3c7367e1ed4fc9c20e0a26e79551b1454d72583c97cc6610"
+dependencies = [
+ "windows-core",
+]
+
+[[package]]
+name = "windows-core"
+version = "0.62.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b8e83a14d34d0623b51dce9581199302a221863196a1dde71a7663a4c2be9deb"
+dependencies = [
+ "windows-implement",
+ "windows-interface",
+ "windows-link",
+ "windows-result",
+ "windows-strings",
+]
+
+[[package]]
+name = "windows-future"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e1d6f90251fe18a279739e78025bd6ddc52a7e22f921070ccdc67dde84c605cb"
+dependencies = [
+ "windows-core",
+ "windows-link",
+ "windows-threading",
+]
+
+[[package]]
+name = "windows-implement"
+version = "0.60.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "053e2e040ab57b9dc951b72c264860db7eb3b0200ba345b4e4c3b14f67855ddf"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "windows-interface"
+version = "0.59.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3f316c4a2570ba26bbec722032c4099d8c8bc095efccdc15688708623367e358"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "windows-link"
 version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
 
+[[package]]
+name = "windows-numerics"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e2e40844ac143cdb44aead537bbf727de9b044e107a0f1220392177d15b0f26"
+dependencies = [
+ "windows-core",
+ "windows-link",
+]
+
+[[package]]
+name = "windows-result"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7781fa89eaf60850ac3d2da7af8e5242a5ea78d1a11c49bf2910bb5a73853eb5"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
+name = "windows-strings"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7837d08f69c77cf6b07689544538e017c1bfcf57e34b4c0ff58e6c2cd3b37091"
+dependencies = [
+ "windows-link",
+]
+
 [[package]]
 name = "windows-sys"
 version = "0.61.2"
@@ -1693,6 +1868,15 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "windows-threading"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3949bd5b99cafdf1c7ca86b43ca564028dfe27d66958f2470940f73d86d75b37"
+dependencies = [
+ "windows-link",
+]
+
 [[package]]
 name = "winnow"
 version = "1.0.1"

Cargo.toml

@@ -2,11 +2,13 @@
 resolver = "3"
 members = [
     "fix",
+    "fix-abstract-vm",
     "fix-builtins",
     "fix-codegen",
     "fix-common",
     "fix-error",
     "fix-ir",
+    "fix-primops",
     "fix-vm",
 ]
 
@@ -27,7 +29,7 @@ bumpalo = { version = "3.20", features = [
 ghost-cell = "0.2"
 hashbrown = "0.16"
 num_enum = "0.7.5"
-smallvec = "1.15"
+smallvec = { version = "1.15", features = ["const_new", "const_generics"] }
 ere = "0.2"
 string-interner = "0.19"
 rnix = "0.14"

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-abstract-vm/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "fix-abstract-vm"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+gc-arena = { workspace = true }
+hashbrown = { workspace = true }
+num_enum = { workspace = true }
+smallvec = { workspace = true }
+string-interner = { workspace = true }
+likely_stable = { workspace = true }
+sptr = "0.3"
+
+fix-builtins = { path = "../fix-builtins" }
+fix-codegen = { path = "../fix-codegen" }
+fix-common = { path = "../fix-common" }
+fix-error = { path = "../fix-error" }

fix-abstract-vm/src/boxing.rs

@@ -24,7 +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;
 }
@@ -157,9 +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 {
@@ -195,7 +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,
@@ -244,7 +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),
@@ -285,17 +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
     }
 
@@ -307,7 +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],
@@ -341,7 +357,7 @@ impl Value {
 
     #[inline]
     #[must_use]
-    pub(crate) fn tag(&self) -> RawTag {
+    pub(crate) const fn tag(&self) -> RawTag {
         self.header.tag()
     }
 
@@ -357,7 +373,7 @@ impl Value {
 
     #[inline]
     #[must_use]
-    pub(crate) fn data(&self) -> &[u8; 6] {
+    pub fn data(&self) -> &[u8; 6] {
         &self.data
     }
 
@@ -417,7 +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 {
@@ -433,7 +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-abstract-vm/src/bytecode_reader.rs

@@ -0,0 +1,142 @@
+#![allow(dead_code)]
+
+use fix_codegen::OperandType;
+use fix_common::StringId;
+use num_enum::TryFromPrimitive;
+use string_interner::Symbol as _;
+
+use crate::{OperandData, VmRuntimeCtx};
+
+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) -> fix_codegen::Op {
+        use fix_codegen::Op;
+        self.inst_start_pc = self.pc;
+        let byte = self.bytecode[self.pc];
+        if !likely_stable::likely((0..Op::Illegal as u8).contains(&byte)) {
+            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<C: VmRuntimeCtx>(&mut self, ctx: &C) -> 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 => {
+                let id = self.read_u32();
+                OperandData::Const(ctx.get_const(id))
+            }
+            OperandType::BigInt => {
+                let val = self.read_i64();
+                OperandData::BigInt(val)
+            }
+            OperandType::Local => {
+                let layer = self.read_u8();
+                let idx = self.read_u32();
+                OperandData::Local { layer, idx }
+            }
+            OperandType::BuiltinConst => {
+                let id = self.read_string_id();
+                OperandData::BuiltinConst(id)
+            }
+            OperandType::Builtins => OperandData::Builtins,
+            OperandType::ReplBinding => {
+                let id = self.read_string_id();
+                OperandData::ReplBinding(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-abstract-vm/src/forced.rs

@@ -0,0 +1,272 @@
+use fix_common::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-abstract-vm/src/host.rs

@@ -0,0 +1,164 @@
+use fix_codegen::InstructionPtr;
+use fix_common::StringId;
+use fix_error::Source;
+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_common::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_common::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_common::Value;
+}
+
+impl<T: VmRuntimeCtx> ConvertValueWithSeen for T {
+    fn convert_value_with_seen(&self, val: Value, seen: &mut HashSet<u64>) -> fix_common::Value {
+        use fix_common::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_common::Symbol::from(key), converted);
+            }
+            Value::AttrSet(fix_common::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_common::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 = fix_builtins::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 = fix_builtins::BUILTINS[app.primop.id as usize].0;
+            Value::PrimOpApp(name.strip_prefix("__").unwrap_or(name))
+        } else {
+            Value::Null
+        }
+    }
+}

fix-abstract-vm/src/lib.rs

@@ -0,0 +1,20 @@
+mod boxing;
+mod bytecode_reader;
+mod forced;
+mod host;
+mod machine;
+mod path_util;
+mod resolve;
+mod state;
+mod string_context;
+mod value;
+
+pub use bytecode_reader::*;
+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-abstract-vm/src/machine.rs

@@ -0,0 +1,174 @@
+use std::ops::ControlFlow;
+use std::path::{Path, PathBuf};
+
+use fix_common::StringId;
+use fix_error::Error;
+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>);
+    fn pop(&mut self) -> Value<'gc>;
+    fn peek(&self, depth: usize) -> Value<'gc>;
+    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 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_common::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-abstract-vm/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-abstract-vm/src/resolve.rs

@@ -0,0 +1,33 @@
+use gc_arena::{Gc, Mutation};
+
+use crate::{AttrSet, Machine, OperandData, Value};
+
+/// 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>,
+    m: &M,
+) -> Value<'gc> {
+    use OperandData::*;
+    match *op {
+        Const(sv) => sv.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-abstract-vm/src/state.rs

@@ -0,0 +1,99 @@
+use std::ops::ControlFlow;
+use std::path::PathBuf;
+
+use fix_common::StringId;
+use fix_error::Error;
+use gc_arena::{Collect, Gc};
+use hashbrown::HashSet;
+
+use crate::{GcEnv, StaticValue, 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,
+    },
+}
+
+pub enum OperandData {
+    Const(StaticValue),
+    BigInt(i64),
+    Local { layer: u8, idx: u32 },
+    BuiltinConst(StringId),
+    Builtins,
+    ReplBinding(StringId),
+    ScopedImportBinding { slot_id: u32, name: StringId },
+}

fix-abstract-vm/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-abstract-vm/src/value.rs

@@ -1,5 +1,6 @@
 #![allow(dead_code)]
 
+use std::cell::RefCell;
 use std::fmt;
 use std::marker::PhantomData;
 use std::mem::size_of;
@@ -7,6 +8,7 @@ use std::ops::Deref;
 
 use fix_builtins::BuiltinId;
 use fix_common::*;
+use gc_arena::barrier::Unlock;
 use gc_arena::collect::Trace;
 use gc_arena::{Collect, Gc, GcRefLock, Mutation, RefLock};
 use num_enum::TryFromPrimitive;
@@ -14,8 +16,8 @@ use smallvec::SmallVec;
 use string_interner::Symbol;
 use string_interner::symbol::SymbolU32;
 
-use crate::NixNum;
 use crate::boxing::{RawBox, RawStore, RawTag, Value as RawValue};
+use crate::string_context::StringContext;
 
 mod private {
     pub trait Cealed {}
@@ -23,11 +25,12 @@ mod private {
 
 /// # Safety
 ///
-/// 1. TAG must be unique among all implementors.
+/// TAG must be unique among all implementors.
-/// 2. TAG must be within 1..=7
+#[allow(private_interfaces)]
 pub unsafe trait Storable: private::Cealed {
-    const TAG: (bool, u8);
+    const TAG: RawTag;
 }
+#[allow(private_bounds)]
 pub trait InlineStorable: Storable + RawStore {}
 pub trait GcStorable: Storable {}
 
@@ -37,15 +40,17 @@ macro_rules! define_value_types {
         gc { $($gtype:ty => $gtag:expr, $gname:literal;)* }
     ) => {
         $(
+        #[allow(private_interfaces)]
         unsafe impl Storable for $itype {
-            const TAG: (bool, u8) = $itag;
+            const TAG: RawTag = $itag;
         }
         impl InlineStorable for $itype {}
         impl private::Cealed for $itype {}
         )*
         $(
+        #[allow(private_interfaces)]
         unsafe impl Storable for $gtype {
-            const TAG: (bool, u8) = $gtag;
+            const TAG: RawTag = $gtag;
         }
         impl GcStorable for $gtype {}
         impl private::Cealed for $gtype {}
@@ -53,11 +58,9 @@ macro_rules! define_value_types {
 
         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 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;
@@ -79,12 +82,12 @@ macro_rules! define_value_types {
             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() {
+                match tag {
                     $(<$gtype as Storable>::TAG => unsafe {
                         self.load_gc::<$gtype>().trace(cc)
                     },)*
                     $(<$itype as Storable>::TAG => (),)*
-                    (neg, val) => unreachable!("invalid tag: neg={neg}, val={val}"),
+                    _ => unreachable!("invalid value tag"),
                 }
             }
         }
@@ -100,7 +103,7 @@ macro_rules! define_value_types {
                     }),)*
                     $(Some(<$gtype as Storable>::TAG) =>
                         write!(f, "{}(..)", $gname),)*
-                    Some((neg, val)) => write!(f, "Unknown(neg={neg}, val={val})"),
+                    _ => unreachable!("invalid value tag"),
                 }
             }
         }
@@ -109,20 +112,21 @@ macro_rules! define_value_types {
 
 define_value_types! {
     inline {
-        i32 => (false, 1), "SmallInt";
+        i32 => RawTag::P1, "SmallInt";
-        bool => (false, 2), "Bool";
+        bool => RawTag::P2, "Bool";
-        Null => (false, 3), "Null";
+        Null => RawTag::P3, "Null";
-        StringId => (false, 4), "SmallString";
+        StringId => RawTag::P4, "SmallString";
-        PrimOp => (false, 5), "PrimOp";
+        PrimOp => RawTag::P5, "PrimOp";
+        Path => RawTag::N6, "Path";
     }
     gc {
-        i64 => (false, 6), "BigInt";
+        i64 => RawTag::P6, "BigInt";
-        NixString => (false, 7), "String";
+        NixString => RawTag::P7, "String";
-        AttrSet<'_> => (true, 1), "AttrSet";
+        AttrSet<'_> => RawTag::N1, "AttrSet";
-        List<'_> => (true, 2), "List";
+        List<'_> => RawTag::N2, "List";
-        Thunk<'_> => (true, 3), "Thunk";
+        Thunk<'_> => RawTag::N3, "Thunk";
-        Closure<'_> => (true, 4), "Closure";
+        Closure<'_> => RawTag::N4, "Closure";
-        PrimOpApp<'_> => (true, 5), "PrimOpApp";
+        PrimOpApp<'_> => RawTag::N5, "PrimOpApp";
     }
 }
 
@@ -131,7 +135,7 @@ define_value_types! {
 /// NaN-boxed value fitting in 8 bytes.
 #[derive(Copy, Clone)]
 #[repr(transparent)]
-pub(crate) struct Value<'gc> {
+pub struct Value<'gc> {
     raw: RawBox,
     _marker: PhantomData<Gc<'gc, ()>>,
 }
@@ -166,16 +170,15 @@ impl<'gc> Value<'gc> {
         }
     }
 
-    /// Returns the `(negative, val)` tag, or `None` for a float.
     #[inline(always)]
-    fn tag(self) -> Option<(bool, u8)> {
+    const fn tag(self) -> Option<RawTag> {
-        self.raw.tag().map(|t| t.neg_val())
+        self.raw.tag()
     }
 }
 
 impl<'gc> Value<'gc> {
     #[inline]
-    pub(crate) fn new_float(val: f64) -> Self {
+    pub fn new_float(val: f64) -> Self {
         Self {
             raw: RawBox::from_float(val),
             _marker: PhantomData,
@@ -183,24 +186,18 @@ impl<'gc> Value<'gc> {
     }
 
     #[inline]
-    pub(crate) fn new_inline<T: InlineStorable>(val: T) -> Self {
+    pub fn new_inline<T: InlineStorable>(val: T) -> Self {
-        Self::from_raw_value(RawValue::store(
+        Self::from_raw_value(RawValue::store(T::TAG, val))
-            unsafe { RawTag::new_unchecked(T::TAG.0, T::TAG.1) },
-            val,
-        ))
     }
 
     #[inline]
-    pub(crate) fn new_gc<T: GcStorable>(gc: Gc<'gc, T>) -> Self {
+    pub fn new_gc<T: GcStorable>(gc: Gc<'gc, T>) -> Self {
         let ptr = Gc::as_ptr(gc);
-        Self::from_raw_value(RawValue::store(
+        Self::from_raw_value(RawValue::store(T::TAG, ptr))
-            unsafe { RawTag::new_unchecked(T::TAG.0, T::TAG.1) },
-            ptr,
-        ))
     }
 
     #[inline]
-    pub(crate) fn make_int(val: i64, mc: &Mutation<'gc>) -> Self {
+    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 {
@@ -211,24 +208,24 @@ impl<'gc> Value<'gc> {
 
 impl<'gc> Value<'gc> {
     #[inline]
-    pub(crate) fn is_float(self) -> bool {
+    pub fn is_float(self) -> bool {
         self.raw.is_float()
     }
 
     #[inline]
-    pub(crate) fn is<T: Storable>(self) -> bool {
+    pub fn is<T: Storable>(self) -> bool {
         self.tag() == Some(T::TAG)
     }
 }
 
 impl<'gc> Value<'gc> {
     #[inline]
-    pub(crate) fn as_float(self) -> Option<f64> {
+    pub fn as_float(self) -> Option<f64> {
         self.raw.float().copied()
     }
 
     #[inline]
-    pub(crate) fn as_inline<T: InlineStorable>(self) -> Option<T> {
+    pub fn as_inline<T: InlineStorable>(self) -> Option<T> {
         if self.is::<T>() {
             Some(unsafe {
                 let rv = self.raw.value().unwrap_unchecked();
@@ -240,7 +237,7 @@ impl<'gc> Value<'gc> {
     }
 
     #[inline]
-    pub(crate) fn as_gc<T: GcStorable>(self) -> Option<Gc<'gc, T>> {
+    pub fn as_gc<T: GcStorable>(self) -> Option<Gc<'gc, T>> {
         if self.is::<T>() {
             Some(unsafe {
                 let rv = self.raw.value().unwrap_unchecked();
@@ -253,7 +250,12 @@ impl<'gc> Value<'gc> {
     }
 
     #[inline]
-    pub(crate) fn as_num(self) -> Option<NixNum> {
+    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>() {
@@ -264,13 +266,71 @@ impl<'gc> Value<'gc> {
     }
 
     #[inline]
-    pub(crate) fn restrict(self) -> Result<StrictValue<'gc>, Gc<'gc, Thunk<'gc>>> {
+    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]
+    pub fn expect_inline<T: InlineStorable>(self) -> Result<T, NixType> {
+        self.as_inline::<T>().ok_or_else(|| self.ty())
+    }
+
+    #[inline]
+    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)]
@@ -295,8 +355,12 @@ impl StaticValue {
         Self(Value::new_inline(val))
     }
     #[inline]
-    pub fn new_primop(id: BuiltinId, arity: u8) -> Self {
+    pub fn new_primop(id: BuiltinId, arity: u8, dispatch_ip: u32) -> Self {
-        Self(Value::new_inline(PrimOp { id, arity }))
+        Self(Value::new_inline(PrimOp {
+            id,
+            arity,
+            dispatch_ip,
+        }))
     }
     #[inline]
     pub fn is_float(self) -> bool {
@@ -321,7 +385,7 @@ impl StaticValue {
 }
 
 #[derive(Clone, Copy, Debug)]
-pub(crate) struct Null;
+pub struct Null;
 impl RawStore for Null {
     fn to_val(self, value: &mut RawValue) {
         value.set_data([0; 6]);
@@ -343,26 +407,55 @@ impl RawStore for StringId {
     }
 }
 
-/// Heap-allocated Nix string.
+/// A canonicalized absolute path. Inline value carrying an interned
-///
+/// `StringId` whose contents are the path's absolute, dot-resolved form.
-/// Stored on the GC heap via `Gc<'gc, NixString>`. The string data itself
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-/// lives in a standard `Box<str>` owned by this struct; the GC only manages
+pub struct Path(pub StringId);
-/// the outer allocation.
+
+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(crate) struct NixString {
+pub struct NixString {
     data: Box<str>,
-    // TODO: string context for derivation dependency tracking
+    context: StringContext,
 }
 
 impl NixString {
-    pub(crate) fn new(s: impl Into<Box<str>>) -> Self {
+    pub fn new(s: impl Into<Box<str>>) -> Self {
-        Self { data: s.into() }
+        Self {
+            data: s.into(),
+            context: StringContext::new(),
+        }
     }
 
-    pub(crate) fn as_str(&self) -> &str {
+    /// 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 {
@@ -373,35 +466,28 @@ impl fmt::Debug for NixString {
 
 #[derive(Collect, Debug, Default)]
 #[collect(no_drop)]
-pub(crate) struct AttrSet<'gc> {
+pub struct AttrSet<'gc> {
-    entries: SmallVec<[(StringId, Value<'gc>); 4]>,
+    pub 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) fn from_sorted_unchecked(entries: SmallVec<[(StringId, Value<'gc>); 4]>) -> Self {
+    pub 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>> {
+    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(crate) fn has(&self, key: StringId) -> bool {
+    pub 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> {
+    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));
@@ -437,64 +523,70 @@ impl<'gc> AttrSet<'gc> {
 }
 
 #[derive(Collect, Debug, Default)]
+#[repr(transparent)]
 #[collect(no_drop)]
-pub(crate) struct List<'gc> {
+pub struct List<'gc> {
-    pub(crate) inner: SmallVec<[Value<'gc>; 4]>,
+    pub inner: RefLock<SmallVec<[Value<'gc>; 4]>>,
 }
-impl<'gc> Deref for List<'gc> {
+
-    type Target = SmallVec<[Value<'gc>; 4]>;
+impl<'gc> List<'gc> {
-    fn deref(&self) -> &Self::Target {
+    pub fn new(mc: &Mutation<'gc>, data: SmallVec<[Value<'gc>; 4]>) -> Gc<'gc, Self> {
-        &self.inner
+        Gc::new(
+            mc,
+            Self {
+                inner: RefLock::new(data),
+            },
+        )
+    }
+
+    pub fn new_gc(mc: &Mutation<'gc>) -> Gc<'gc, Self> {
+        Gc::new(mc, Self::default())
     }
 }
 
-pub(crate) type Thunk<'gc> = RefLock<ThunkState<'gc>>;
+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(crate) enum ThunkState<'gc> {
+pub enum ThunkState<'gc> {
-    Pending {
+    Pending { ip: usize, env: GcEnv<'gc> },
-        ip: usize,
+    Apply { func: Value<'gc>, arg: Value<'gc> },
-        env: GcEnv<'gc>,
-        with_env: Option<GcWithEnv<'gc>>,
-    },
-    Apply {
-        func: Value<'gc>,
-        arg: Value<'gc>,
-    },
     Blackhole,
     Evaluated(StrictValue<'gc>),
 }
 
 #[derive(Collect, Debug)]
 #[collect(no_drop)]
-pub(crate) struct Env<'gc> {
+pub struct Env<'gc> {
-    pub(crate) locals: SmallVec<[Value<'gc>; 4]>,
+    pub locals: SmallVec<[Value<'gc>; 4]>,
-    pub(crate) prev: Option<GcEnv<'gc>>,
+    pub prev: Option<GcEnv<'gc>>,
 }
-pub(crate) type GcEnv<'gc> = GcRefLock<'gc, Env<'gc>>;
+pub type GcEnv<'gc> = GcRefLock<'gc, Env<'gc>>;
 
 #[derive(Collect, Debug)]
 #[collect(no_drop)]
-pub(crate) struct WithEnv<'gc> {
+pub struct WithEnv<'gc> {
-    pub(crate) env: Value<'gc>,
+    pub env: Value<'gc>,
-    pub(crate) prev: Option<GcWithEnv<'gc>>,
+    pub prev: Option<GcWithEnv<'gc>>,
 }
-pub(crate) type GcWithEnv<'gc> = Gc<'gc, WithEnv<'gc>>;
+pub type GcWithEnv<'gc> = Gc<'gc, WithEnv<'gc>>;
 
 impl<'gc> Env<'gc> {
-    pub(crate) fn empty() -> Self {
+    pub fn empty() -> Self {
         Env {
             locals: SmallVec::new(),
             prev: None,
         }
     }
 
-    pub(crate) fn with_arg(
+    pub fn with_arg(arg: Value<'gc>, n_locals: u32, prev: Gc<'gc, RefLock<Env<'gc>>>) -> Self {
-        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 {
@@ -506,56 +598,69 @@ impl<'gc> Env<'gc> {
 
 #[derive(Collect, Debug)]
 #[collect(no_drop)]
-pub(crate) struct Closure<'gc> {
+pub struct Closure<'gc> {
-    pub(crate) ip: u32,
+    pub ip: u32,
-    pub(crate) n_locals: u32,
+    pub n_locals: u32,
-    pub(crate) env: Gc<'gc, RefLock<Env<'gc>>>,
+    pub env: Gc<'gc, RefLock<Env<'gc>>>,
-    pub(crate) pattern: Option<Gc<'gc, PatternInfo>>,
+    pub pattern: Option<Gc<'gc, PatternInfo>>,
 }
 
 #[derive(Collect, Debug)]
 #[collect(require_static)]
-pub(crate) struct PatternInfo {
+pub struct PatternInfo {
-    pub(crate) required: SmallVec<[StringId; 4]>,
+    pub required: SmallVec<[StringId; 4]>,
-    pub(crate) optional: SmallVec<[StringId; 4]>,
+    pub optional: SmallVec<[StringId; 4]>,
-    pub(crate) ellipsis: bool,
+    pub ellipsis: bool,
-    pub(crate) param_spans: Box<[(StringId, u32)]>,
+    pub param_spans: Box<[(StringId, u32)]>,
 }
 
+#[repr(packed, Rust)]
 #[derive(Clone, Copy, Debug, Collect)]
 #[collect(require_static)]
-pub(crate) struct PrimOp {
+pub struct PrimOp {
-    pub(crate) id: BuiltinId,
+    pub id: BuiltinId,
-    pub(crate) arity: u8,
+    pub arity: u8,
+    pub dispatch_ip: u32,
 }
 
 impl RawStore for PrimOp {
     fn to_val(self, value: &mut RawValue) {
-        value.set_data([0, 0, 0, 0, self.id as u8, self.arity]);
+        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] = *value.data();
+        let [id, arity, bytes @ ..] = *value.data();
         Self {
             id: BuiltinId::try_from_primitive(id).expect("invalid BuiltinId"),
             arity,
+            dispatch_ip: u32::from_le_bytes(bytes),
         }
     }
 }
 
 #[derive(Collect, Debug)]
 #[collect(no_drop)]
-pub(crate) struct PrimOpApp<'gc> {
+pub struct PrimOpApp<'gc> {
-    pub(crate) primop: PrimOp,
+    pub primop: PrimOp,
-    pub(crate) args: SmallVec<[Value<'gc>; 2]>,
+    pub arity: u8,
+    pub args: [Value<'gc>; 3],
 }
 
-#[derive(Copy, Clone, Default)]
+#[derive(Copy, Clone, Default, Collect)]
 #[repr(transparent)]
-pub(crate) struct StrictValue<'gc>(Value<'gc>);
+#[collect(no_drop)]
+pub struct StrictValue<'gc>(Value<'gc>);
 
 impl<'gc> StrictValue<'gc> {
     #[inline]
-    pub(crate) fn relax(self) -> Value<'gc> {
+    pub fn relax(self) -> Value<'gc> {
         self.0
     }
 }
@@ -574,9 +679,50 @@ impl fmt::Debug for StrictValue<'_> {
     }
 }
 
-unsafe impl<'gc> Collect<'gc> for StrictValue<'gc> {
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Collect)]
-    const NEEDS_TRACE: bool = true;
+#[collect(require_static)]
-    fn trace<T: gc_arena::collect::Trace<'gc>>(&self, cc: &mut T) {
+pub enum NixType {
-        self.0.trace(cc);
+    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-builtins/src/lib.rs

@@ -88,7 +88,6 @@ define_builtins! {
     ("__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),
@@ -119,7 +118,282 @@ define_builtins! {
     ("__tryEval",                  TryEval,                  1),
     ("__typeOf",                   TypeOf,                   1),
     ("__unsafeDiscardStringContext", UnsafeDiscardStringContext, 1),
+    ("__unsafeDiscardOutputDependency", UnsafeDiscardOutputDependency, 1),
     ("__unsafeGetAttrPos",         UnsafeGetAttrPos,         2),
     ("__warn",                     Warn,                     2),
     ("__zipAttrsWith",             ZipAttrsWith,             2),
 }
+
+#[repr(u8)]
+#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
+pub enum PrimOpPhase {
+    Abort,
+    Add,
+    AddErrorContext,
+    All,
+    Any,
+    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,
+
+    // TODO: split into separate enums
+    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 BuiltinId {
+    #[inline(always)]
+    pub fn entry_phase(self) -> PrimOpPhase {
+        use BuiltinId::*;
+        match self {
+            Abort => PrimOpPhase::Abort,
+            Add => PrimOpPhase::Add,
+            AddErrorContext => PrimOpPhase::AddErrorContext,
+            All => PrimOpPhase::All,
+            Any => PrimOpPhase::Any,
+            AppendContext => PrimOpPhase::AppendContext,
+            AttrNames => PrimOpPhase::AttrNames,
+            AttrValues => PrimOpPhase::AttrValues,
+            BaseNameOf => PrimOpPhase::BaseNameOf,
+            BitAnd => PrimOpPhase::BitAnd,
+            BitOr => PrimOpPhase::BitOr,
+            BitXor => PrimOpPhase::BitXor,
+            Break => PrimOpPhase::Break,
+            CatAttrs => PrimOpPhase::CatAttrs,
+            Ceil => PrimOpPhase::Ceil,
+            CompareVersions => PrimOpPhase::CompareVersions,
+            ConcatLists => PrimOpPhase::ConcatLists,
+            ConcatMap => PrimOpPhase::ConcatMap,
+            ConcatStringsSep => PrimOpPhase::ConcatStringsSep,
+            ConvertHash => PrimOpPhase::ConvertHash,
+            DeepSeq => PrimOpPhase::DeepSeq,
+            Derivation => PrimOpPhase::Derivation,
+            DerivationStrict => PrimOpPhase::DerivationStrict,
+            DirOf => PrimOpPhase::DirOf,
+            Div => PrimOpPhase::Div,
+            Elem => PrimOpPhase::Elem,
+            ElemAt => PrimOpPhase::ElemAt,
+            FetchGit => PrimOpPhase::FetchGit,
+            FetchMercurial => PrimOpPhase::FetchMercurial,
+            FetchTarball => PrimOpPhase::FetchTarball,
+            FetchTree => PrimOpPhase::FetchTree,
+            FetchUrl => PrimOpPhase::FetchUrl,
+            Filter => PrimOpPhase::FilterForceList,
+            FilterSource => PrimOpPhase::FilterSource,
+            FindFile => PrimOpPhase::FindFile,
+            Floor => PrimOpPhase::Floor,
+            FoldlStrict => PrimOpPhase::FoldlStrict,
+            FromJSON => PrimOpPhase::FromJSON,
+            FromTOML => PrimOpPhase::FromTOML,
+            FunctionArgs => PrimOpPhase::FunctionArgs,
+            GenList => PrimOpPhase::GenList,
+            GenericClosure => PrimOpPhase::GenericClosure,
+            GetAttr => PrimOpPhase::GetAttr,
+            GetContext => PrimOpPhase::GetContext,
+            GetEnv => PrimOpPhase::GetEnv,
+            GroupBy => PrimOpPhase::GroupBy,
+            HasAttr => PrimOpPhase::HasAttr,
+            HasContext => PrimOpPhase::HasContext,
+            HashFile => PrimOpPhase::HashFile,
+            HashString => PrimOpPhase::HashString,
+            Head => PrimOpPhase::Head,
+            Import => PrimOpPhase::Import,
+            IntersectAttrs => PrimOpPhase::IntersectAttrs,
+            IsAttrs => PrimOpPhase::IsAttrs,
+            IsBool => PrimOpPhase::IsBool,
+            IsFloat => PrimOpPhase::IsFloat,
+            IsFunction => PrimOpPhase::IsFunction,
+            IsInt => PrimOpPhase::IsInt,
+            IsList => PrimOpPhase::IsList,
+            IsNull => PrimOpPhase::IsNull,
+            IsPath => PrimOpPhase::IsPath,
+            IsString => PrimOpPhase::IsString,
+            Length => PrimOpPhase::Length,
+            LessThan => PrimOpPhase::LessThan,
+            ListToAttrs => PrimOpPhase::ListToAttrs,
+            Map => PrimOpPhase::Map,
+            MapAttrs => PrimOpPhase::MapAttrs,
+            Match => PrimOpPhase::Match,
+            Mul => PrimOpPhase::Mul,
+            ParseDrvName => PrimOpPhase::ParseDrvName,
+            Partition => PrimOpPhase::Partition,
+            Path => PrimOpPhase::Path,
+            PathExists => PrimOpPhase::PathExists,
+            Placeholder => PrimOpPhase::Placeholder,
+            ReadDir => PrimOpPhase::ReadDir,
+            ReadFile => PrimOpPhase::ReadFile,
+            ReadFileType => PrimOpPhase::ReadFileType,
+            RemoveAttrs => PrimOpPhase::RemoveAttrs,
+            ReplaceStrings => PrimOpPhase::ReplaceStrings,
+            ScopedImport => PrimOpPhase::ScopedImport,
+            Seq => PrimOpPhase::Seq,
+            Sort => PrimOpPhase::Sort,
+            Split => PrimOpPhase::Split,
+            SplitVersion => PrimOpPhase::SplitVersion,
+            StorePath => PrimOpPhase::StorePath,
+            StringLength => PrimOpPhase::StringLength,
+            Sub => PrimOpPhase::Sub,
+            Substring => PrimOpPhase::Substring,
+            Tail => PrimOpPhase::Tail,
+            Throw => PrimOpPhase::Throw,
+            ToFile => PrimOpPhase::ToFile,
+            ToJSON => PrimOpPhase::ToJSON,
+            ToPath => PrimOpPhase::ToPath,
+            ToString => PrimOpPhase::ToString,
+            ToXML => PrimOpPhase::ToXML,
+            Trace => PrimOpPhase::Trace,
+            TryEval => PrimOpPhase::TryEval,
+            TypeOf => PrimOpPhase::TypeOf,
+            UnsafeDiscardStringContext => PrimOpPhase::UnsafeDiscardStringContext,
+            UnsafeDiscardOutputDependency => PrimOpPhase::UnsafeDiscardOutputDependency,
+            UnsafeGetAttrPos => PrimOpPhase::UnsafeGetAttrPos,
+            Warn => PrimOpPhase::Warn,
+            ZipAttrsWith => PrimOpPhase::ZipAttrsWith,
+        }
+    }
+}
+
+impl PrimOpPhase {
+    pub fn ip(self) -> u32 {
+        self as u32 * 2
+    }
+}

fix-codegen/src/disassembler.rs

@@ -1,9 +1,10 @@
 use std::fmt::Write;
 
 use colored::Colorize;
+use fix_builtins::BuiltinId;
 use num_enum::TryFromPrimitive;
 
-use crate::{InstructionPtr, Op};
+use crate::{InstructionPtr, Op, OperandType};
 
 pub trait DisassemblerContext {
     fn resolve_string(&self, id: u32) -> &str;
@@ -25,12 +26,14 @@ 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 +42,7 @@ 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 +51,7 @@ 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 +60,7 @@ 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 +69,7 @@ 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 +78,36 @@ 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_primitive(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)
     }
@@ -255,34 +292,94 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
                 ("MakePatternClosure", arg_str)
             }
 
-            Op::Call => ("Call", String::new()),
+            Op::Call => {
+                self.read_operand_data();
+                ("Call", "arg=?".into())
+            }
+            Op::DispatchPrimOp => {
+                let id = BuiltinId::try_from_primitive(self.read_u8()).expect("invalid builtin id");
+                ("DispatchPrimOp", format!("id={id:?}"))
+            }
 
             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()),
@@ -326,18 +423,25 @@ 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.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()),
@@ -345,19 +449,16 @@ 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.resolve_string(idx);
                 ("LoadReplBinding", format!("{:?}", name))
             }
             Op::LoadScopedBinding => {
+                let slot = self.read_u32();
                 let idx = self.read_u32();
                 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-codegen/src/lib.rs

@@ -1,6 +1,4 @@
-use std::ops::Deref;
+use fix_builtins::{BUILTINS, BuiltinId};
-
-use fix_builtins::BuiltinId;
 use fix_common::StringId;
 use fix_ir::{Attr, BinOpKind, Ir, MaybeThunk, Param, RawIrRef, ThunkId, UnOpKind};
 use hashbrown::HashMap;
@@ -18,6 +16,8 @@ pub trait BytecodeContext {
     fn get_code(&self) -> &[u8];
     fn get_code_mut(&mut self) -> &mut Vec<u8>;
     fn add_constant(&mut self, val: Const) -> u32;
+    fn current_source_dir(&mut self) -> StringId;
+    fn current_scope_slot(&self) -> Option<u32>;
 }
 
 #[repr(u8)]
@@ -42,12 +42,19 @@ pub enum Op {
     MakePatternClosure,
 
     Call,
+    DispatchPrimOp,
 
     MakeAttrs,
     MakeEmptyAttrs,
-    Select,
+    SelectStatic,
-    SelectDefault,
+    SelectDynamic,
-    HasAttr,
+    HasAttrPathStatic,
+    HasAttrPathDynamic,
+    HasAttrStatic,
+    HasAttrDynamic,
+    HasAttrResolve,
+    JumpIfSelectSucceeded,
+    JumpIfSelectFailed,
 
     MakeList,
     MakeEmptyList,
@@ -72,20 +79,18 @@ pub enum Op {
     JumpIfTrue,
     Jump,
 
+    CoerceToString,
+
     ConcatStrings,
     ResolvePath,
 
     Assert,
 
-    PushWith,
+    LookupWith,
-    PopWith,
-    WithLookup,
 
     LoadBuiltins,
     LoadBuiltin,
 
-    MkPos,
-
     LoadReplBinding,
     LoadScopedBinding,
 
@@ -95,7 +100,7 @@ pub enum Op {
 }
 
 struct ScopeInfo {
-    depth: u16,
+    depth: u8,
     thunk_map: HashMap<ThunkId, u32>,
 }
 
@@ -108,9 +113,26 @@ struct BytecodeEmitter<'a, Ctx: BytecodeContext> {
 #[derive(Debug, Clone, Copy, TryFromPrimitive)]
 pub enum OperandType {
     Const,
-    Local,
-    Builtins,
     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)]
@@ -120,20 +142,14 @@ pub enum AttrKeyType {
     Dynamic,
 }
 
-pub enum Const {
-    Smi(i32),
-    Float(f64),
-    Bool(bool),
-    String(StringId),
-    PrimOp { id: BuiltinId, arity: u8 },
-    Null,
-}
-
 pub enum InlineOperand {
     Const(Const),
-    Local { layer: u16, local: u32 },
-    Builtins,
     BigInt(i64),
+    Local { layer: u8, local: u32 },
+    BuiltinConst(StringId),
+    Builtins,
+    ReplBinding(StringId),
+    ScopedImportBinding(StringId),
 }
 
 pub fn compile_bytecode(ir: RawIrRef<'_>, ctx: &mut impl BytecodeContext) -> InstructionPtr {
@@ -151,12 +167,13 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         }
     }
 
-    fn inline_maybe_thunk(&mut self, val: MaybeThunk) -> InlineOperand {
+    #[must_use]
+    fn inline_maybe_thunk(&self, val: &MaybeThunk) -> InlineOperand {
         use MaybeThunk::*;
-        match val {
+        match *val {
             Int(x) => {
-                if x <= i32::MAX as i64 {
+                if let Ok(x) = x.try_into() {
-                    InlineOperand::Const(Const::Smi(x as i32))
+                    InlineOperand::Const(Const::Smi(x))
                 } else {
                     InlineOperand::BigInt(x)
                 }
@@ -165,38 +182,65 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             Bool(b) => InlineOperand::Const(Const::Bool(b)),
             Null => InlineOperand::Const(Const::Null),
             Str(id) => InlineOperand::Const(Const::String(id)),
+            Path(id) => InlineOperand::Const(Const::String(id)),
             Thunk(id) => {
                 let (layer, local) = self.resolve_thunk(id);
                 InlineOperand::Local { layer, local }
             }
-            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 {
-            _ => panic!("cannot classify IR node as inline operand"),
+                    id,
+                    arity,
+                    dispatch_ip: id.entry_phase().ip(),
+                })
+            }
+            BuiltinConst(id) => InlineOperand::BuiltinConst(id),
+            Builtins => InlineOperand::Builtins,
+            ReplBinding(id) => InlineOperand::ReplBinding(id),
+            ScopedImportBinding(id) => InlineOperand::ScopedImportBinding(id),
         }
     }
 
-    fn emit_maybe_thunk(&mut self, val: MaybeThunk) {
+    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(OperandType::Const as u8);
                 self.emit_u32(idx);
             }
-            InlineOperand::Local { layer, local } => {
+            BigInt(val) => {
-                self.emit_u8(OperandType::Local as u8);
-                self.emit_u8(layer as u8);
-                self.emit_u32(local);
-            }
-            InlineOperand::Builtins => {
-                self.emit_u8(OperandType::Builtins as u8);
-            }
-            InlineOperand::BigInt(val) => {
                 self.emit_u8(OperandType::BigInt as u8);
                 self.emit_i64(val);
             }
+            Local { layer, local } => {
+                self.emit_u8(OperandType::Local as u8);
+                self.emit_u8(layer);
+                self.emit_u32(local);
+            }
+            BuiltinConst(id) => {
+                self.emit_u8(OperandType::BuiltinConst as u8);
+                self.emit_str_id(id);
+            }
+            Builtins => {
+                self.emit_u8(OperandType::Builtins as u8);
+            }
+            ReplBinding(id) => {
+                self.emit_u8(OperandType::ReplBinding as u8);
+                self.emit_str_id(id);
+            }
+            ScopedImportBinding(id) => {
+                self.emit_u8(OperandType::ScopedImportBinding as u8);
+                let slot = self
+                    .ctx
+                    .current_scope_slot()
+                    .expect("ScopedImportBinding outside scoped compilation");
+                self.emit_u32(slot);
+                self.emit_str_id(id);
+            }
         }
     }
 
@@ -205,6 +249,11 @@ 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);
@@ -276,11 +325,11 @@ 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;
@@ -290,111 +339,19 @@ 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, .. } => self.count_with_thunks(*func),
-            Ir::Assert {
-                assertion, expr, ..
-            } => self.count_with_thunks(*assertion) + self.count_with_thunks(*expr),
-            Ir::Select { expr, .. } => self.count_with_thunks(*expr),
-            Ir::HasAttr { lhs, .. } => self.count_with_thunks(*lhs),
-            Ir::ConcatStrings { parts, .. } => {
-                parts.iter().map(|p| self.count_with_thunks(*p)).sum()
-            }
-            _ => 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, .. } => {
-                self.collect_with_thunks_recursive(*func, out);
-            }
-            Ir::Assert {
-                assertion, expr, ..
-            } => {
-                self.collect_with_thunks_recursive(*assertion, out);
-                self.collect_with_thunks_recursive(*expr, out);
-            }
-            Ir::Select { expr, .. } => {
-                self.collect_with_thunks_recursive(*expr, 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);
-                }
-            }
-            _ => (),
-        }
-    }
-
     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()
@@ -409,19 +366,13 @@ 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);
@@ -455,11 +406,11 @@ 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);
@@ -479,6 +430,8 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             &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);
@@ -538,10 +491,10 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             &Ir::Call { func, arg, .. } => {
                 self.emit_expr(func);
                 self.emit_op(Op::Call);
-                self.inline_maybe_thunk(arg);
+                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);
@@ -554,10 +507,6 @@ 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);
             }
@@ -567,24 +516,23 @@ 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(),
                 );
             }
             &Ir::ConcatStrings {
-                parts: _,
+                ref parts,
-                force_string: _,
+                force_string,
             } => {
-                todo!("redesign ConcatStrings");
+                for &part in parts.iter() {
-                // self.emit_op(Op::ConcatStrings);
+                    self.emit_expr(part);
-                // self.emit_u16(parts.len() as u16);
+                    self.emit_op(Op::CoerceToString);
-                // self.emit_u8(if force_string { 1 } else { 0 });
+                }
-                // for &part in parts.iter() {
+                self.emit_op(Op::ConcatStrings);
-                //     let operand = self.inline_maybe_thunk(part);
+                self.emit_u16(parts.len() as u16);
-                //     self.emit_inline_operand(operand);
+                self.emit_bool(force_string);
-                // }
             }
             &Ir::HasAttr { lhs, ref rhs } => {
                 self.emit_has_attr(lhs, rhs);
@@ -598,15 +546,10 @@ 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);
@@ -614,19 +557,89 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             }
             &Ir::ScopedImportBinding(name) => {
                 self.emit_op(Op::LoadScopedBinding);
+                let slot = self
+                    .ctx
+                    .current_scope_slot()
+                    .expect("ScopedImportBinding outside scoped compilation");
+                self.emit_u32(slot);
                 self.emit_str_id(name);
             }
-            &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) => {
+            }
-                self.emit_op(Op::WithLookup);
+            &Ir::MaybeThunk(thunk) => {
+                use MaybeThunk::*;
+                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(name) => {
+                        self.emit_op(Op::LoadScopedBinding);
+                        let slot = self
+                            .ctx
+                            .current_scope_slot()
+                            .expect("ScopedImportBinding outside scoped compilation");
+                        self.emit_u32(slot);
+                        self.emit_str_id(name);
+                    }
+                }
+            }
         }
     }
 
@@ -690,16 +703,6 @@ 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::Call);
-            }
-            PipeR => {
-                self.emit_expr(lhs);
-                self.emit_expr(rhs);
-                self.emit_op(Op::Call);
-            }
             _ => {
                 self.emit_expr(lhs);
                 self.emit_expr(rhs);
@@ -722,17 +725,13 @@ 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;
@@ -751,10 +750,10 @@ 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);
@@ -770,39 +769,39 @@ 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: &fix_ir::HashMap<'_, StringId, (MaybeThunk, TextRange)>,
+        stcs: &fix_ir::HashMap<'_, StringId, (&MaybeThunk, TextRange)>,
-        dyns: &[(RawIrRef<'_>, MaybeThunk, 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(AttrKeyType::Static as u8);
             self.emit_str_id(sym);
             self.emit_maybe_thunk(val);
             let span_id = self.ctx.register_span(span);
             self.emit_u32(span_id);
         }
-        for &(_key, _val, _span) in dyns.iter() {
+
-            todo!("redesign dynamic attr key");
+        for &(_key, val, span) in dyns.iter() {
-            // self.emit_u8(AttrKeyType::Dynamic as u8);
+            self.emit_maybe_thunk(val);
-            // self.emit_maybe_thunk(key);
+            let span_id = self.ctx.register_span(span);
-            // let val_operand = self.inline_maybe_thunk(val);
+            self.emit_u32(span_id);
-            // self.emit_maybe_thunk(val);
-            // let span_id = self.ctx.register_span(span);
-            // self.emit_u32(span_id);
         }
     }
 
@@ -814,69 +813,87 @@ 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(AttrKeyType::Static as u8);
+                    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(AttrKeyType::Dynamic as u8);
+                    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(AttrKeyType::Static as u8);
+                    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(AttrKeyType::Dynamic as u8);
+                    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, _) => {
+                self.emit_op(Op::HasAttrStatic);
+                self.emit_str_id(sym);
             }
-
+            Attr::Dynamic(key_expr, _) => {
-    fn emit_with(
+                self.emit_op(Op::JumpIfSelectFailed);
-        &mut self,
+                dynamic_patches.push(self.emit_i32_placeholder());
-        namespace: MaybeThunk,
+                self.emit_expr(key_expr);
-        body: RawIrRef<'_>,
+                self.emit_op(Op::HasAttrDynamic);
-        thunks: &[(ThunkId, RawIrRef<'_>)],
+            }
-    ) {
+        }
-        self.emit_op(Op::PushWith);
+        for patch in dynamic_patches {
-        self.emit_maybe_thunk(namespace);
+            self.patch_jump_target(patch);
-        self.emit_scope_thunks(thunks);
+        }
-        self.emit_expr(body);
+        self.emit_op(Op::HasAttrResolve);
-        self.emit_op(Op::PopWith);
     }
 
     fn emit_toplevel_inner(&mut self, body: RawIrRef<'_>, thunks: &[(ThunkId, RawIrRef<'_>)]) {

fix-common/src/lib.rs

@@ -272,9 +272,9 @@ 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,

fix-ir/src/downgrade.rs

@@ -39,12 +39,12 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, T, E: std::fmt::Display>
 }
 
 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>) -> MaybeThunk;
+    fn maybe_thunk(&mut self, ir: GhostRoIrRef<'id, 'ir>) -> GhostRoMaybeThunkRef<'id, 'ir>;
 
     fn intern_string(&mut self, sym: impl AsRef<str>) -> StringId;
     fn resolve_sym(&self, id: StringId) -> Symbol<'_>;
-    fn lookup(&self, sym: StringId, span: TextRange) -> Result<MaybeThunk>;
+    fn lookup(&mut self, sym: StringId, span: TextRange) -> Result<GhostRoMaybeThunkRef<'id, 'ir>>;
 
     fn get_current_source(&self) -> Source;
 
@@ -53,11 +53,11 @@ 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;
 
@@ -65,11 +65,11 @@ 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),
@@ -98,7 +98,7 @@ 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
@@ -114,7 +114,7 @@ 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();
@@ -130,7 +130,7 @@ 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)?;
@@ -142,7 +142,7 @@ 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>> {
                 downgrade_path(self.parts(), ctx)
             }
         }
@@ -152,7 +152,7 @@ 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)?;
@@ -180,7 +180,7 @@ 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::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(_)));
@@ -210,7 +210,7 @@ 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::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();
         let expr = match self.kind() {
             ast::LiteralKind::Integer(int) => Ir::Int(int.value().require(ctx, span)?),
@@ -225,16 +225,73 @@ 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::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.intern_string(text);
-        ctx.lookup(sym, span).map(|thunk| thunk.to_ir(ctx))
+        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)?;
@@ -250,7 +307,7 @@ 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()
@@ -264,17 +321,52 @@ 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)?;
@@ -283,7 +375,7 @@ 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();
@@ -292,7 +384,7 @@ 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::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)?;
@@ -311,7 +403,7 @@ 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| {
@@ -340,7 +432,7 @@ 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)?;
@@ -350,33 +442,25 @@ 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| {
@@ -433,7 +517,7 @@ 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)?;
@@ -835,8 +919,15 @@ fn make_attrpath_value_entry<'ir>(path: Vec<'ir, ast::Attr>, value: ast::Expr) -
 }
 
 struct FinalizedAttrSet<'id, 'ir> {
-    stcs: HashMap<'ir, StringId, (MaybeThunk, TextRange)>,
+    stcs: HashMap<'ir, StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
-    dyns: Vec<'ir, (IrRef<'id, 'ir>, MaybeThunk, TextRange)>,
+    dyns: Vec<
+        'ir,
+        (
+            GhostRoIrRef<'id, 'ir>,
+            GhostRoMaybeThunkRef<'id, 'ir>,
+            TextRange,
+        ),
+    >,
 }
 
 fn downgrade_attrs<'id, 'ir>(
@@ -851,7 +942,7 @@ 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 {
@@ -912,7 +1003,7 @@ 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()
@@ -921,7 +1012,7 @@ 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)>,
 }
@@ -930,7 +1021,7 @@ 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>,
@@ -989,6 +1080,7 @@ 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()
@@ -1000,21 +1092,16 @@ where
                     span,
                 } = param;
                 let default = default.map(|default| default.downgrade(ctx)).transpose()?;
-                // let default = if let Some(default) = default {
-                //     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)?;
@@ -1034,10 +1121,10 @@ 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)
@@ -1047,7 +1134,7 @@ 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>,
 {
@@ -1068,14 +1155,18 @@ 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>, MaybeThunk, 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)?;
@@ -1090,7 +1181,7 @@ where
         let vals = {
             let mut temp = Vec::with_capacity_in(keys.len(), ctx.bump());
             for sym in &keys {
-                temp.push(finalized.stcs.get(sym).expect("WTF").0.to_ir(ctx));
+                temp.push(finalized.stcs.get(sym).expect("WTF").0);
             }
             temp
         };
@@ -1101,7 +1192,7 @@ where
 fn collect_inherit_lookups<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>>(
     entries: &[ast::Entry],
     ctx: &mut Ctx,
-) -> Result<HashMap<'ir, StringId, (MaybeThunk, 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
@@ -1141,7 +1232,7 @@ 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, (MaybeThunk, TextRange)>,
+    inherit_lookups: &HashMap<StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
     ctx: &mut Ctx,
 ) -> Result<FinalizedAttrSet<'id, 'ir>> {
     let mut stcs = HashMap::new_in(ctx.bump());
@@ -1169,9 +1260,9 @@ 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, (MaybeThunk, 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) => expr.downgrade(ctx),
         PendingValue::InheritFrom(from_expr, sym, span) => {
@@ -1185,9 +1276,10 @@ fn finalize_pending_value<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW
         }
         PendingValue::InheritScope(sym, span) => {
             if let Some(&(expr, _)) = inherit_lookups.get(&sym) {
-                Ok(expr.to_ir(ctx))
+                Ok(ctx.new_expr(Ir::MaybeThunk(expr)))
             } else {
-                ctx.lookup(sym, span).map(|val| val.to_ir(ctx))
+                ctx.lookup(sym, span)
+                    .map(|val| ctx.new_expr(Ir::MaybeThunk(val)))
             }
         }
         PendingValue::Set(set) => {
@@ -1210,7 +1302,7 @@ 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>>,
     ctx: &mut impl DowngradeContext<'id, 'ir>,
-) -> Result<IrRef<'id, 'ir>> {
+) -> Result<GhostRoIrRef<'id, 'ir>> {
     let bump = ctx.bump();
     let parts = parts
         .into_iter()

fix-ir/src/lib.rs

@@ -1,5 +1,5 @@
 use std::hash::Hash;
-use std::ops::Deref;
+use std::marker::PhantomData;
 
 use bumpalo::Bump;
 use bumpalo::collections::Vec;
@@ -10,56 +10,70 @@ use num_enum::TryFromPrimitive as _;
 use rnix::{TextRange, ast};
 use string_interner::DefaultStringInterner;
 
-use crate::downgrade::DowngradeContext;
-
 pub mod downgrade;
 
 pub type HashMap<'ir, K, V> = hashbrown::HashMap<K, V, hashbrown::DefaultHashBuilder, &'ir Bump>;
 
-#[repr(transparent)]
+pub type GhostIrRef<'id, 'ir> = <GhostRef<'id, 'ir> as RefExt<'ir>>::IrRef;
-#[derive(Clone, Copy)]
+pub type GhostRoIrRef<'id, 'ir> = <GhostRoRef<'id, 'ir> as RefExt<'ir>>::IrRef;
-pub struct IrRef<'id, 'ir>(&'ir GhostCell<'id, Ir<'ir, Self>>);
+pub type RawIrRef<'ir> = <RawRef<'ir> as RefExt<'ir>>::IrRef;
-
+pub type GhostMaybeThunkRef<'id, 'ir> = <GhostRef<'id, 'ir> as RefExt<'ir>>::MaybeThunkRef;
-impl<'id, 'ir> IrRef<'id, 'ir> {
+pub type GhostRoMaybeThunkRef<'id, 'ir> = <GhostRoRef<'id, 'ir> as RefExt<'ir>>::MaybeThunkRef;
-    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)
-    }
 
+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
+        // SAFETY: The transmute is sound because:
-    /// The transmute is sound because:
+        // - `GhostCell<'id, T>` is `#[repr(transparent)]` over `T`, so
-    /// - `GhostCell<'id, T>` is `#[repr(transparent)]` over `T`
+        //   `&'ir GhostCell<'id, T>` and `&'ir T` have identical layout.
-    /// - `IrRef<'id, 'ir>` is `#[repr(transparent)]` over
+        // - `Ir<'ir, R>` is `#[repr(C)]`, and for every field that depends on
-    ///   `&'ir GhostCell<'id, Ir<'ir, Self>>`
+        //   `R`, instantiating `R = GhostRef<'id, 'ir>` vs `R = RawRef<'ir>`
-    /// - `RawIrRef<'ir>` is `#[repr(transparent)]` over `&'ir Ir<'ir, Self>`
+        //   produces types of identical layout:
-    /// - `Ir<'ir, Ref>` is `#[repr(C)]` and both ref types are pointer-sized
+        //     - `R::IrRef` becomes `&'ir GhostCell<'id, Ir<...>>` vs `&'ir Ir<...>`
-    ///
+        //     - `R::MaybeThunkRef` becomes `&'ir GhostCell<'id, MaybeThunk>`
-    /// Consuming the `GhostToken` guarantees no `borrow_mut` calls can occur
+        //       vs `&'ir MaybeThunk`
-    /// afterwards, so the shared `&Ir` references from `RawIrRef::Deref` can
+        //     - `R::Ref<Ir<'ir, R>>` (used in `ConcatStrings::parts`) reduces
-    /// never alias with mutable references.
+        //       to the same case as `R::IrRef`
-    pub fn freeze(self, _token: GhostToken<'id>) -> RawIrRef<'ir> {
+        // - Therefore `IrRef<'id, 'ir>` and `RawIrRef<'ir>` are both
-        unsafe { std::mem::transmute(self) }
+        //   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)]
-#[derive(Clone, Copy, Debug)]
+pub struct GhostRoCell<'id, T: ?Sized>(GhostCell<'id, T>);
-pub struct RawIrRef<'ir>(pub &'ir Ir<'ir, Self>);
 
-impl<'ir> Deref for RawIrRef<'ir> {
+impl<'id, T> From<GhostCell<'id, T>> for GhostRoCell<'id, T> {
-    type Target = Ir<'ir, RawIrRef<'ir>>;
+    fn from(value: GhostCell<'id, T>) -> Self {
-    fn deref(&self) -> &Self::Target {
+        Self(value)
-        self.0
+    }
+}
+
+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)
     }
 }
 
@@ -73,110 +87,117 @@ pub enum MaybeThunk {
     Str(StringId),
     Path(StringId),
     Thunk(ThunkId),
-    Arg { layer: usize },
+    Arg { layer: u8 },
     Builtin(BuiltinId),
+    BuiltinConst(StringId),
     Builtins,
     ReplBinding(StringId),
     ScopedImportBinding(StringId),
-    WithLookup(StringId),
 }
 
-impl MaybeThunk {
+pub trait Ref<'ir> {
-    fn to_ir<'id, 'ir>(self, ctx: &mut impl DowngradeContext<'id, 'ir>) -> IrRef<'id, 'ir> {
+    type Ref<T>
-        use MaybeThunk::*;
+    where
-        let ir = match self {
+        T: 'ir;
-            Int(x) => Ir::Int(x),
-            Float(x) => Ir::Float(x),
-            Bool(x) => Ir::Bool(x),
-            Null => Ir::Null,
-            Str(x) => Ir::Str(x),
-            Path(x) => Ir::Path(ctx.new_expr(Ir::Str(x))),
-            Thunk(x) => Ir::Thunk(x),
-            Arg { layer } => Ir::Arg { layer },
-            Builtin(x) => Ir::Builtin(x),
-            Builtins => Ir::Builtins,
-            ReplBinding(x) => Ir::ReplBinding(x),
-            ScopedImportBinding(x) => Ir::ScopedImportBinding(x),
-            WithLookup(x) => Ir::WithLookup(x),
-        };
-        ctx.new_expr(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, Ref> {
+pub enum Ir<'ir, R: RefExt<'ir> + ?Sized + 'ir> {
     Int(i64),
     Float(f64),
     Bool(bool),
     Null,
     Str(StringId),
-    Path(Ref),
+    Path(R::IrRef),
     AttrSet {
-        stcs: HashMap<'ir, StringId, (MaybeThunk, TextRange)>,
+        stcs: HashMap<'ir, StringId, (R::MaybeThunkRef, TextRange)>,
-        dyns: Vec<'ir, (Ref, MaybeThunk, TextRange)>,
+        dyns: Vec<'ir, (R::IrRef, R::MaybeThunkRef, TextRange)>,
     },
     List {
-        items: Vec<'ir, MaybeThunk>,
+        items: Vec<'ir, R::MaybeThunkRef>,
     },
     ConcatStrings {
-        parts: Vec<'ir, Ref>,
+        parts: Vec<'ir, R::Ref<Ir<'ir, R>>>,
         force_string: bool,
     },
 
     // OPs
     UnOp {
-        rhs: Ref,
+        rhs: R::IrRef,
         kind: UnOpKind,
     },
     BinOp {
-        lhs: Ref,
+        lhs: R::IrRef,
-        rhs: Ref,
+        rhs: R::IrRef,
         kind: BinOpKind,
     },
     HasAttr {
-        lhs: Ref,
+        lhs: R::IrRef,
-        rhs: Vec<'ir, Attr<Ref>>,
+        rhs: Vec<'ir, Attr<R::IrRef>>,
     },
     Select {
-        expr: Ref,
+        expr: R::IrRef,
-        attrpath: Vec<'ir, Attr<Ref>>,
+        attrpath: Vec<'ir, Attr<R::IrRef>>,
-        default: Option<Ref>,
+        default: Option<R::IrRef>,
         span: TextRange,
     },
 
     // Conditionals
     If {
-        cond: Ref,
+        cond: R::IrRef,
-        consq: Ref,
+        consq: R::IrRef,
-        alter: Ref,
+        alter: R::IrRef,
     },
     Assert {
-        assertion: Ref,
+        assertion: R::IrRef,
-        expr: Ref,
+        expr: R::IrRef,
         assertion_raw: String,
         span: TextRange,
     },
 
-    With {
+    WithLookup {
-        namespace: MaybeThunk,
+        sym: StringId,
-        body: Ref,
+        namespaces: Vec<'ir, R::MaybeThunkRef>,
-        thunks: Vec<'ir, (ThunkId, Ref)>,
     },
-    WithLookup(StringId),
 
     // Function related
     Func {
-        body: Ref,
+        body: R::IrRef,
         param: Option<Param<'ir>>,
-        thunks: Vec<'ir, (ThunkId, Ref)>,
+        thunks: Vec<'ir, (ThunkId, R::IrRef)>,
     },
     Arg {
-        layer: usize,
+        layer: u8,
     },
     Call {
-        func: Ref,
+        func: R::IrRef,
-        arg: MaybeThunk,
+        arg: R::MaybeThunkRef,
         span: TextRange,
     },
 
@@ -187,11 +208,10 @@ pub enum Ir<'ir, Ref> {
 
     // Misc
     TopLevel {
-        body: Ref,
+        body: R::IrRef,
-        thunks: Vec<'ir, (ThunkId, Ref)>,
+        thunks: Vec<'ir, (ThunkId, R::IrRef)>,
     },
-    Thunk(ThunkId),
+    MaybeThunk(R::MaybeThunkRef),
-    CurPos(TextRange),
     ReplBinding(StringId),
     ScopedImportBinding(StringId),
 }
@@ -241,36 +261,6 @@ pub enum BinOpKind {
     // 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.
@@ -299,38 +289,38 @@ pub struct Param<'ir> {
 
 pub fn new_global_env(
     strings: &mut DefaultStringInterner,
-) -> hashbrown::HashMap<StringId, Ir<'static, RawIrRef<'static>>> {
+) -> 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, Ir::Builtins);
+    global_env.insert(builtins_sym, MaybeThunk::Builtins);
 
     for (idx, &(name, _)) in BUILTINS.iter().enumerate() {
         let id = BuiltinId::try_from_primitive(idx as u8).expect("infallible");
         let name = StringId(strings.get_or_intern(name));
-        global_env.insert(name, Ir::Builtin(id));
+        global_env.insert(name, MaybeThunk::Builtin(id));
     }
 
     let consts = [
         (
             "__currentSystem",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("currentSystem"))),
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("currentSystem"))),
         ),
-        ("__langVersion", Ir::Int(6)),
+        ("__langVersion", MaybeThunk::Int(6)),
         (
             "__nixVersion",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("nixVersion"))),
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("nixVersion"))),
         ),
         (
             "__storeDir",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("storeDir"))),
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("storeDir"))),
         ),
         (
             "__nixPath",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("nixPath"))),
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("nixPath"))),
         ),
-        ("null", Ir::Null),
+        ("null", MaybeThunk::Null),
-        ("true", Ir::Bool(true)),
+        ("true", MaybeThunk::Bool(true)),
-        ("false", Ir::Bool(false)),
+        ("false", MaybeThunk::Bool(false)),
     ];
 
     for (name, ir) in consts {

fix-primops/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "fix-primops"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+gc-arena = { workspace = true }
+hashbrown = { workspace = true }
+num_enum = { workspace = true }
+smallvec = { workspace = true }
+string-interner = { workspace = true }
+
+fix-abstract-vm = { path = "../fix-abstract-vm" }
+fix-builtins = { path = "../fix-builtins" }
+fix-codegen = { path = "../fix-codegen" }
+fix-common = { path = "../fix-common" }
+fix-error = { path = "../fix-error" }

fix-primops/src/context.rs

@@ -0,0 +1,447 @@
+//! `builtins.hasContext`, `builtins.getContext`, `builtins.appendContext`,
+//! `builtins.unsafeDiscardStringContext`,
+//! `builtins.unsafeDiscardOutputDependency`.
+//!
+//! See `fix-abstract-vm/src/string_context.rs` for the
+//! `StringContextElem` type.
+
+use fix_abstract_vm::{
+    AttrSet, BytecodeReader, List as VmList, Machine, MachineExt, NixString, NixType, Step,
+    StrictValue, StringContext, StringContextElem, Value, VmRuntimeCtx, VmRuntimeCtxExt,
+};
+use fix_builtins::PrimOpPhase;
+use fix_common::StringId;
+use fix_error::Error;
+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-primops/src/control.rs

@@ -0,0 +1,362 @@
+use fix_abstract_vm::{
+    AttrSet, BytecodeReader, Closure, Env, List, Machine, MachineExt, Step, StrictValue, Value,
+    VmRuntimeCtx, VmRuntimeCtxExt,
+};
+use fix_builtins::PrimOpPhase;
+use fix_error::Error;
+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-primops/src/conv.rs

@@ -0,0 +1,51 @@
+use fix_abstract_vm::{
+    BytecodeReader, Machine, MachineExt, NixString, NixType, Path, Step, StrictValue, Value,
+    VmRuntimeCtx,
+};
+use fix_common::StringId;
+use fix_error::Error;
+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-primops/src/eq.rs

@@ -0,0 +1,238 @@
+use fix_abstract_vm::{
+    AttrSet, BytecodeReader, CallFrame, List, Machine, MachineExt, NixNum, Null, Path, Step,
+    StrictValue, Value, VmRuntimeCtx, VmRuntimeCtxExt,
+};
+use fix_builtins::PrimOpPhase;
+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-primops/src/io.rs

@@ -0,0 +1,190 @@
+use std::path::PathBuf;
+
+use fix_abstract_vm::{
+    AttrSet, Break, BytecodeReader, CallFrame, Machine, MachineExt, Path, PendingLoad,
+    PendingScope, Step, StrictValue, Value, VmRuntimeCtx, VmRuntimeCtxExt, canon_path_str,
+};
+use fix_builtins::PrimOpPhase;
+use fix_common::StringId;
+use fix_error::Error;
+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-primops/src/lib.rs

@@ -0,0 +1,87 @@
+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_abstract_vm::{BytecodeReader, Machine, Step, VmRuntimeCtx};
+use fix_builtins::PrimOpPhase;
+use fix_error::Error;
+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),
+
+        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-primops/src/list.rs

@@ -0,0 +1,166 @@
+use fix_abstract_vm::{
+    BytecodeReader, List, Machine, MachineExt, NixType, Step, StrictValue, Value,
+};
+use fix_builtins::PrimOpPhase;
+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();
+        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(())
+}

fix-primops/src/path.rs

@@ -0,0 +1,43 @@
+use fix_abstract_vm::{
+    BytecodeReader, Machine, MachineExt, Path, Step, StrictValue, Value, VmRuntimeCtx,
+    VmRuntimeCtxExt, canon_path_str,
+};
+use fix_error::Error;
+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-vm/Cargo.toml

@@ -3,6 +3,9 @@ name = "fix-vm"
 version = "0.1.0"
 edition = "2024"
 
+[features]
+tailcall = []
+
 [dependencies]
 gc-arena = { workspace = true }
 hashbrown = { workspace = true }
@@ -11,8 +14,11 @@ smallvec = { workspace = true }
 string-interner = { workspace = true }
 likely_stable = { workspace = true }
 sptr = "0.3"
+sysinfo = { version = "0.38", default-features = false, features = ["system"] }
 
 fix-builtins = { path = "../fix-builtins" }
 fix-codegen = { path = "../fix-codegen" }
 fix-common = { path = "../fix-common" }
 fix-error = { path = "../fix-error" }
+fix-abstract-vm = { path = "../fix-abstract-vm" }
+fix-primops = { path = "../fix-primops" }

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 $name<'gc, C: VmRuntimeCtx>(
+            vm: &mut Vm<'gc>,
+            mc: &Mutation<'gc>,
+            ctx: &mut C,
+            bc: &[u8],
+            table: &DispatchTable<'gc, C>,
+            pc: u32,
+            fuel: u32,
+        ) -> TailResult {
+            let result = vm.$name();
+            tail_dispatch_after!(result, pc + 1, vm, mc, ctx, bc, table, fuel)
+        }
+    };
+    ($name:ident, (reader)) => {
+        extern "rust-preserve-none" fn $name<'gc, C: VmRuntimeCtx>(
+            vm: &mut Vm<'gc>,
+            mc: &Mutation<'gc>,
+            ctx: &mut C,
+            bc: &[u8],
+            table: &DispatchTable<'gc, C>,
+            pc: u32,
+            fuel: u32,
+        ) -> TailResult {
+            let mut reader = BytecodeReader::from_after_op(bc, pc as usize);
+            let result = vm.$name(&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 $name<'gc, C: VmRuntimeCtx>(
+            vm: &mut Vm<'gc>,
+            mc: &Mutation<'gc>,
+            ctx: &mut C,
+            bc: &[u8],
+            table: &DispatchTable<'gc, C>,
+            pc: u32,
+            fuel: u32,
+        ) -> TailResult {
+            let mut reader = BytecodeReader::from_after_op(bc, pc as usize);
+            let result = vm.$name(&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 $name<'gc, C: VmRuntimeCtx>(
+            vm: &mut Vm<'gc>,
+            mc: &Mutation<'gc>,
+            ctx: &mut C,
+            bc: &[u8],
+            table: &DispatchTable<'gc, C>,
+            pc: u32,
+            fuel: u32,
+        ) -> TailResult {
+            let mut reader = BytecodeReader::from_after_op(bc, pc as usize);
+            let result = vm.$name(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 $name<'gc, C: VmRuntimeCtx>(
+            vm: &mut Vm<'gc>,
+            mc: &Mutation<'gc>,
+            ctx: &mut C,
+            bc: &[u8],
+            table: &DispatchTable<'gc, C>,
+            pc: u32,
+            fuel: u32,
+        ) -> TailResult {
+            let result = vm.$name(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];
+                $( arr[fix_codegen::Op::$variant as usize] = $fn; )*
+                DispatchTable(arr)
+            };
+        }
+
+        // Exhaustiveness check: fails to compile if `fix_codegen::Op` gains,
+        // loses, or renames a variant that isn't wired up above.
+        #[allow(dead_code)]
+        const _: fn(fix_codegen::Op) = |op| match op {
+            $( fix_codegen::Op::$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/helpers.rs

@@ -1,18 +0,0 @@
-use fix_error::Error;
-
-use crate::value::StrictValue;
-use crate::{NixNum, VmError};
-
-pub(super) fn vm_err(msg: impl Into<String>) -> VmError {
-    VmError::Uncatchable(Error::eval_error(msg.into()))
-}
-
-pub(super) fn get_num(val: StrictValue<'_>) -> Option<NixNum> {
-    if let Some(i) = val.as_inline::<i32>() {
-        Some(NixNum::Int(i as i64))
-    } else if let Some(gc_i) = val.as_gc::<i64>() {
-        Some(NixNum::Int(*gc_i))
-    } else {
-        val.as_float().map(NixNum::Float)
-    }
-}

fix-vm/src/instructions/arithmetic.rs

@@ -0,0 +1,297 @@
+use std::cmp::Ordering;
+
+use fix_abstract_vm::*;
+use gc_arena::{Gc, Mutation, RefLock};
+
+use crate::{BytecodeReader, NixNum, Step, VmError, VmRuntimeCtx};
+
+impl<'gc> crate::Vm<'gc> {
+    #[inline(always)]
+    pub(crate) fn op_add(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let (lhs, rhs) = self.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 self.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);
+            self.push(Value::new_inline(fix_abstract_vm::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),
+            );
+            self.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) => {
+                self.push(val);
+                Step::Continue(())
+            }
+            Err(e) => self.finish_vm_err(e),
+        }
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_sub(&mut self, reader: &mut BytecodeReader<'_>, mc: &Mutation<'gc>) -> Step {
+        self.op_arith(reader, mc, i64::wrapping_sub, |a, b| a - b)
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_mul(&mut self, reader: &mut BytecodeReader<'_>, mc: &Mutation<'gc>) -> Step {
+        self.op_arith(reader, mc, i64::wrapping_mul, |a, b| a * b)
+    }
+
+    #[inline(always)]
+    fn op_arith(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        int_op: fn(i64, i64) -> i64,
+        float_op: fn(f64, f64) -> f64,
+    ) -> Step {
+        let (lhs, rhs) = self.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+        let res = numeric_binop(lhs, rhs, mc, int_op, float_op);
+        match res {
+            Ok(val) => {
+                self.push(val);
+                Step::Continue(())
+            }
+            Err(e) => self.finish_vm_err(e),
+        }
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_div(&mut self, reader: &mut BytecodeReader<'_>, mc: &Mutation<'gc>) -> Step {
+        let (lhs, rhs) = self.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+        match (get_num(lhs), get_num(rhs)) {
+            (_, Some(NixNum::Int(0))) | (_, Some(NixNum::Float(0.))) => {
+                return self.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) => {
+                self.push(val);
+                Step::Continue(())
+            }
+            Err(e) => self.finish_vm_err(e),
+        }
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_eq(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let (lhs, rhs) = self.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+        fix_primops::start_eq(self, ctx, reader, mc, lhs, rhs, false)
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_neq(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let (lhs, rhs) = self.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+        fix_primops::start_eq(self, ctx, reader, mc, lhs, rhs, true)
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_lt(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        self.compare_values(ctx, reader, mc, Ordering::is_lt)
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_gt(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        self.compare_values(ctx, reader, mc, Ordering::is_gt)
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_leq(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        self.compare_values(ctx, reader, mc, Ordering::is_le)
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_geq(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        self.compare_values(ctx, reader, mc, Ordering::is_ge)
+    }
+
+    fn compare_values(
+        &mut self,
+        ctx: &impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        pred: fn(Ordering) -> bool,
+    ) -> Step {
+        let (lhs, rhs) = self.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+        match self.compare_values_inner(ctx, pred, lhs, rhs) {
+            Ok(()) => Step::Continue(()),
+            Err(e) => self.finish_vm_err(e),
+        }
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_concat(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let (l, r) = self.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());
+        self.push(Value::new_gc(Gc::new(
+            mc,
+            crate::List {
+                inner: RefLock::new(items),
+            },
+        )));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_update(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let (l, r) = self.force_and_retry::<(Gc<AttrSet>, Gc<AttrSet>)>(reader, mc)?;
+        self.push(Value::new_gc(l.merge(&r, mc)));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_neg(&mut self, reader: &mut BytecodeReader<'_>, mc: &Mutation<'gc>) -> Step {
+        let rhs = self.force_and_retry::<NixNum>(reader, mc)?;
+        match rhs {
+            NixNum::Int(int) => self.push(Value::make_int(-int, mc)),
+            NixNum::Float(float) => self.push(Value::new_float(-float)),
+        }
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_not(&mut self, reader: &mut BytecodeReader<'_>, mc: &Mutation<'gc>) -> Step {
+        let rhs = self.force_and_retry::<bool>(reader, mc)?;
+        self.push(Value::new_inline(!rhs));
+        Step::Continue(())
+    }
+
+    fn compare_values_inner(
+        &mut self,
+        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)
+                }
+            };
+            self.push(Value::new_inline(pred(ord)));
+            return Ok(());
+        }
+        if let (Some(a), Some(b)) = (ctx.get_string(lhs), ctx.get_string(rhs)) {
+            self.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);
+            self.push(Value::new_inline(pred(a.cmp(b))));
+            return Ok(());
+        }
+        // TODO: compare other types
+        Err(crate::vm_err("cannot compare these types"))
+    }
+}
+
+pub(crate) fn get_num(val: StrictValue<'_>) -> Option<NixNum> {
+    if let Some(i) = val.as_inline::<i32>() {
+        Some(NixNum::Int(i as i64))
+    } 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 +1,183 @@
+use fix_abstract_vm::{resolve_operand, *};
+use fix_builtins::PrimOpPhase;
+use fix_error::Error;
+use gc_arena::{Gc, Mutation, RefLock};
+
+use crate::{
+    BytecodeReader, CallFrame, Closure, Env, ForceMode, Step, ThunkState, VmRuntimeCtx,
+    VmRuntimeCtxExt,
+};
+
+impl<'gc> crate::Vm<'gc> {
+    #[inline(always)]
+    pub(crate) fn call(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        arg: Value<'gc>,
+        resume_pc: usize,
+    ) -> Step {
+        let func = self.force_and_retry::<StrictValue>(reader, mc)?;
+        if self.call_depth > 10000 {
+            return self.finish_err(Error::eval_error("stack overflow; max-call-depth exceeded"));
+        }
+        self.call_depth += 1;
+        if let Some(closure) = func.as_gc::<Closure>() {
+            if closure.pattern.is_some() {
+                // FIXME: better DX...
+                self.push(func.relax());
+                self.push(arg);
+                self.call_stack.push(CallFrame {
+                    pc: resume_pc,
+                    thunk: None,
+                    env: self.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)));
+            self.call_stack.push(CallFrame {
+                pc: resume_pc,
+                thunk: None,
+                env: self.env,
+            });
+            reader.set_pc(ip as usize);
+            self.env = new_env;
+        } else if let Some(primop) = func.as_inline::<PrimOp>() {
+            if primop.arity == 1 {
+                self.push(arg);
+                self.call_stack.push(CallFrame {
+                    pc: resume_pc,
+                    thunk: None,
+                    env: self.env,
+                });
+                reader.set_pc(primop.dispatch_ip as usize)
+            } else {
+                let app = PrimOpApp {
+                    primop,
+                    arity: primop.arity - 1,
+                    args: [arg, Value::default(), Value::default()],
+                };
+                self.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 {
+                    self.push(app.args[i as usize]);
+                }
+                self.push(arg);
+                self.call_stack.push(CallFrame {
+                    pc: resume_pc,
+                    thunk: None,
+                    env: self.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;
+                self.push(Value::new_gc(Gc::new(mc, new_app)))
+            }
+        } else if let Some(attrs) = func.as_gc::<AttrSet>()
+            && let Some(functor) = attrs.lookup(self.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.
+            self.call_depth -= 1;
+            self.call_stack.push(CallFrame {
+                pc: resume_pc,
+                thunk: None,
+                env: self.env,
+            });
+            self.push(arg);
+            self.push(func.relax());
+            self.push(functor);
+            reader.set_pc(PrimOpPhase::CallFunctor1.ip() as usize);
+            return Step::Continue(());
+        } else {
+            return self.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(
+        &mut self,
+        ctx: &impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let arg = resolve_operand(&reader.read_operand_data(ctx), mc, self);
+        let pc = reader.pc();
+        self.call(reader, mc, arg, pc)
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_return(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let val = self.force_and_retry::<StrictValue>(reader, mc)?;
+        let Some(CallFrame {
+            pc: ret_pc,
+            thunk,
+            env,
+        }) = self.call_stack.pop()
+        else {
+            match self.force_mode {
+                ForceMode::AsIs => return self.finish_ok(ctx.convert_value(val.relax())),
+                ForceMode::Shallow => {
+                    self.push(val.relax());
+                    reader.set_pc(PrimOpPhase::ForceResultShallow.ip() as usize);
+                    return Step::Continue(());
+                }
+                ForceMode::Deep => {
+                    self.push(val.relax());
+                    self.push(val.relax());
+                    self.call_stack.push(CallFrame {
+                        pc: PrimOpPhase::ForceResultDeepFinish.ip() as usize,
+                        thunk: None,
+                        env: self.env,
+                    });
+                    self.call_depth += 1;
+                    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 {
+            self.call_depth -= 1;
+            self.push(val.relax())
+        }
+        self.env = env;
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_dispatch_primop(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        fix_primops::dispatch_primop(self, ctx, reader, mc)
+    }
+}

fix-vm/src/instructions/closures.rs

@@ -0,0 +1,94 @@
+use gc_arena::{Gc, Mutation, RefLock};
+
+use crate::{BytecodeReader, Step, ThunkState, Value};
+
+impl<'gc> crate::Vm<'gc> {
+    #[inline(always)]
+    pub(crate) fn op_make_thunk(
+        &mut self,
+        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: self.env,
+            }),
+        );
+        self.push(Value::new_gc(thunk));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_make_closure(
+        &mut self,
+        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: self.env,
+                pattern: None,
+            },
+        );
+        self.push(Value::new_gc(closure));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_make_pattern_closure(
+        &mut self,
+        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: self.env,
+                pattern: Some(pattern),
+            },
+        );
+        self.push(Value::new_gc(closure));
+        Step::Continue(())
+    }
+}

fix-vm/src/instructions/collections.rs

@@ -0,0 +1,334 @@
+use fix_abstract_vm::{NixType, resolve_operand};
+use fix_common::StringId;
+use fix_error::Error;
+use gc_arena::{Gc, RefLock};
+use smallvec::SmallVec;
+
+use crate::{
+    AttrSet, BytecodeReader, List, Step, StrictValue, Value, VmRuntimeCtx, VmRuntimeCtxExt,
+};
+
+impl<'gc> crate::Vm<'gc> {
+    #[inline(always)]
+    pub(crate) fn op_make_attrs(
+        &mut self,
+        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;
+            self.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 = self.peek_forced(depth);
+            let key_sid = match ctx.get_string_id(key_val) {
+                Ok(id) => Some(id),
+                Err(NixType::Null) => None,
+                Err(got) => return self.finish_type_err(NixType::String, got),
+            };
+            dyn_keys.push(key_sid);
+        }
+
+        self.stack.truncate(self.stack.len() - 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(ctx), mc, self);
+            let _span_id = reader.read_u32();
+            kv.push((key, val));
+        }
+
+        for key in dyn_keys {
+            let val = resolve_operand(&reader.read_operand_data(ctx), mc, self);
+            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));
+        self.push(Value::new_gc(attrs));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_make_empty_attrs(&mut self) -> Step {
+        self.push(self.empty_attrs);
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_select_static(
+        &mut self,
+        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 = self.force_and_retry::<Gc<AttrSet>>(reader, mc)?;
+
+        match attrset.lookup(key) {
+            Some(v) => {
+                self.push(v);
+            }
+            None => return self.select_skip(key, ctx, reader),
+        }
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_select_dynamic(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &gc_arena::Mutation<'gc>,
+    ) -> Step {
+        let _span_id = reader.read_u32();
+
+        let (attrset, key_val) = self.force_and_retry::<(Gc<AttrSet>, StrictValue)>(reader, mc)?;
+
+        let key_sid = match ctx.get_string_id(key_val) {
+            Ok(id) => id,
+            Err(got) => return self.finish_type_err(NixType::String, got),
+        };
+
+        match attrset.lookup(key_sid) {
+            Some(v) => {
+                self.push(v);
+            }
+            None => return self.select_skip(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(
+        &mut self,
+        key: StringId,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+    ) -> Step {
+        use fix_codegen::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 self
+                        .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(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
+        use fix_codegen::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(
+        &mut self,
+        _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 = self.force_and_retry::<StrictValue>(reader, mc)?;
+
+        match current
+            .as_gc::<AttrSet>()
+            .and_then(|attrs| attrs.lookup(key))
+        {
+            Some(v) => {
+                self.push(v);
+            }
+            None => return self.has_attr_skip(reader),
+        }
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_has_attr_path_dynamic(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &gc_arena::Mutation<'gc>,
+    ) -> Step {
+        let _span_id = reader.read_u32();
+
+        let (current, key_val) = self.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+
+        let key_sid = match ctx.get_string_id(key_val) {
+            Ok(id) => id,
+            Err(got) => return self.finish_type_err(NixType::String, got),
+        };
+
+        match current
+            .as_gc::<AttrSet>()
+            .and_then(|attrs| attrs.lookup(key_sid))
+        {
+            Some(v) => {
+                self.push(v);
+            }
+            None => return self.has_attr_skip(reader),
+        }
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_jump_if_select_failed(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
+        // No-op
+        let _offset = reader.read_i32();
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_jump_if_select_succeeded(&mut self, 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(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &gc_arena::Mutation<'gc>,
+    ) -> Step {
+        let key = reader.read_string_id();
+        let current = self.force_and_retry::<StrictValue>(reader, mc)?;
+
+        self.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(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &gc_arena::Mutation<'gc>,
+    ) -> Step {
+        let (current, dyn_key) = self.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
+
+        let key_sid = match ctx.get_string_id(dyn_key) {
+            Ok(id) => id,
+            Err(got) => return self.finish_type_err(NixType::String, got),
+        };
+
+        self.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(&mut self) -> Step {
+        // If we reach here, has_attr check has failed, push false (AttrSet is already popped)
+        self.push(Value::new_inline(false));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_make_list(
+        &mut self,
+        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(ctx), mc, self));
+        }
+        let list = Gc::new(
+            mc,
+            List {
+                inner: RefLock::new(items),
+            },
+        );
+        self.push(Value::new_gc(list));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_make_empty_list(&mut self) -> Step {
+        self.push(self.empty_list);
+        Step::Continue(())
+    }
+}

fix-vm/src/instructions/control.rs

@@ -0,0 +1,60 @@
+use fix_abstract_vm::*;
+use fix_error::Error;
+use gc_arena::Mutation;
+
+use crate::{BytecodeReader, Step, VmRuntimeCtx};
+
+impl<'gc> crate::Vm<'gc> {
+    #[inline(always)]
+    pub(crate) fn op_jump_if_false(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &gc_arena::Mutation<'gc>,
+    ) -> Step {
+        let offset = reader.read_i32();
+        let cond = self.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(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let offset = reader.read_i32();
+        let cond = self.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(&mut self, 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(
+        &mut self,
+        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 = self.force_and_retry::<bool>(reader, mc)?;
+        if !assertion {
+            // FIXME: use catchable error
+            return self.finish_err(Error::eval_error(format!("assertion '{raw}' failed")));
+        }
+        Step::Continue(())
+    }
+}

fix-vm/src/instructions/literals.rs

@@ -0,0 +1,55 @@
+use gc_arena::{Gc, Mutation};
+
+use crate::{BytecodeReader, Step, Value};
+
+impl<'gc> crate::Vm<'gc> {
+    #[inline(always)]
+    pub(crate) fn op_push_smi(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
+        let val = reader.read_i32();
+        self.push(Value::new_inline(val));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_push_bigint(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let val = reader.read_i64();
+        self.push(Value::new_gc(Gc::new(mc, val)));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_push_float(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
+        let val = reader.read_f64();
+        self.push(Value::new_float(val));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_push_string(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
+        let sid = reader.read_string_id();
+        self.push(Value::new_inline(sid));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_push_null(&mut self) -> Step {
+        self.push(Value::new_inline(crate::Null));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_push_true(&mut self) -> Step {
+        self.push(Value::new_inline(true));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_push_false(&mut self) -> Step {
+        self.push(Value::new_inline(false));
+        Step::Continue(())
+    }
+}

fix-vm/src/instructions/misc.rs

@@ -0,0 +1,183 @@
+use std::path::PathBuf;
+
+use fix_abstract_vm::{
+    AttrSet, NixString, Path, StrictValue, StringContext, canon_path_str
+};
+use fix_builtins::BuiltinId;
+use fix_common::StringId;
+use fix_error::Error;
+use num_enum::TryFromPrimitive;
+
+use crate::{BytecodeReader, PrimOp, Step, Value, VmRuntimeCtx, VmRuntimeCtxExt};
+
+impl<'gc> crate::Vm<'gc> {
+    #[inline(always)]
+    pub(crate) fn op_load_builtins(&mut self) -> Step {
+        self.push(self.builtins);
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_load_builtin(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
+        let Ok(id) = BuiltinId::try_from_primitive(reader.read_u8())
+            .map_err(|err| panic!("unknown builtin id: {}", err.number));
+        self.push(Value::new_inline(PrimOp {
+            id,
+            arity: fix_builtins::BUILTINS[id as usize].1,
+            dispatch_ip: id.entry_phase().ip(),
+        }));
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_load_repl_binding(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
+        let _name = reader.read_string_id();
+        todo!("LoadReplBinding");
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_load_scoped_binding(
+        &mut self,
+        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 = match self.scope_slots.get(slot_id as usize).copied() {
+            Some(s) => s,
+            None => {
+                return self.finish_err(Error::eval_error(format!(
+                    "internal: invalid scope slot {slot_id}"
+                )));
+            }
+        };
+        let Some(attrs) = scope.as_gc::<AttrSet>() else {
+            return self.finish_err(Error::eval_error("internal: scope slot is not an attrset"));
+        };
+        match attrs.lookup(name) {
+            Some(val) => {
+                self.push(val);
+                Step::Continue(())
+            }
+            None => self.finish_err(Error::eval_error(format!(
+                "scoped binding '{}' not found",
+                ctx.resolve_string(name)
+            ))),
+        }
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_coerce_to_string(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &gc_arena::Mutation<'gc>,
+    ) -> Step {
+        let val = self.force_and_retry::<StrictValue>(reader, mc)?;
+        if val.is::<StringId>() || val.is::<NixString>() {
+            self.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
+            self.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(
+        &mut self,
+        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 = self.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 = self.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);
+                }
+            }
+        }
+
+        self.stack.truncate(self.stack.len() - count);
+
+        if merged.is_empty() {
+            let sid = ctx.intern_string(result);
+            self.push(Value::new_inline(sid));
+        } else {
+            let ns = gc_arena::Gc::new(mc, NixString::with_context(result, merged));
+            self.push(Value::new_gc(ns));
+        }
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_resolve_path(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &gc_arena::Mutation<'gc>,
+    ) -> Step {
+        let path_val = self.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>() {
+            self.push(Value::new_inline(p));
+            return Step::Continue(());
+        }
+        let path = match ctx.get_string(path_val) {
+            Some(s) => s.to_owned(),
+            None => {
+                return self.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 self.finish_err(e),
+        };
+        let sid = ctx.intern_string(resolved);
+        self.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 +1,9 @@
+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;

fix-vm/src/instructions/variables.rs

@@ -0,0 +1,50 @@
+use crate::{BytecodeReader, Mutation, Step, Value};
+
+impl<'gc> crate::Vm<'gc> {
+    #[inline(always)]
+    pub(crate) fn op_load_local(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
+        let idx = reader.read_u32() as usize;
+        self.push(self.env.borrow().locals[idx]);
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_load_outer(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
+        let layer = reader.read_u8();
+        let idx = reader.read_u32() as usize;
+        let mut cur = self.env;
+        for _ in 0..layer {
+            let prev = cur.borrow().prev.expect("LoadOuter: env chain too short");
+            cur = prev;
+        }
+        let val = cur.borrow().locals[idx];
+        self.push(val);
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_store_local(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let idx = reader.read_u32() as usize;
+        let val = self.pop();
+        self.env.borrow_mut(mc).locals[idx] = val;
+        Step::Continue(())
+    }
+
+    #[inline(always)]
+    pub(crate) fn op_alloc_locals(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let count = reader.read_u32() as usize;
+        self.env
+            .borrow_mut(mc)
+            .locals
+            .extend(std::iter::repeat_n(Value::default(), count));
+        Step::Continue(())
+    }
+}

fix-vm/src/instructions/with_scope.rs

@@ -0,0 +1,78 @@
+use fix_abstract_vm::{resolve_operand, *};
+use fix_common::Symbol;
+use fix_error::Error;
+use smallvec::SmallVec;
+
+use crate::{Break, BytecodeReader, CallFrame, Step, VmRuntimeCtx};
+
+impl<'gc> crate::Vm<'gc> {
+    #[inline(always)]
+    pub(crate) fn op_lookup_with(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &gc_arena::Mutation<'gc>,
+    ) -> Step {
+        #[allow(clippy::unwrap_used)]
+        let counter = self.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(ctx), mc, self));
+        }
+
+        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;
+                        self.call_stack.push(CallFrame {
+                            thunk: Some(thunk),
+                            pc: resume_pc,
+                            env: self.env,
+                        });
+                        self.env = env;
+                        reader.set_pc(ip);
+                        return Step::Break(Break::Force);
+                    }
+                    ThunkState::Evaluated(v) => v,
+                    ThunkState::Apply { func, arg } => {
+                        self.call_stack.push(CallFrame {
+                            thunk: Some(thunk),
+                            pc: resume_pc,
+                            env: self.env,
+                        });
+                        self.push(func);
+                        return self.call(reader, mc, arg, resume_pc);
+                    }
+                    ThunkState::Blackhole => {
+                        return self
+                            .finish_err(Error::eval_error("infinite recursion encountered"));
+                    }
+                }
+            }
+        };
+
+        if let Some(val) = namespace
+            .as_gc::<AttrSet>()
+            .and_then(|attrs| attrs.lookup(name))
+        {
+            self.replace(0, val);
+        } else if counter + 1 == n as i32 {
+            return self.finish_err(Error::eval_error(format!(
+                "undefined variable '{}'",
+                Symbol::from(ctx.resolve_string(name))
+            )));
+        } else {
+            self.replace(0, Value::new_inline(counter + 1));
+            reader.set_pc(resume_pc);
+        }
+
+        Step::Continue(())
+    }
+}

fix/Cargo.toml

@@ -33,6 +33,8 @@ rnix = { workspace = true }
 ere = { workspace = true }
 ghost-cell = { workspace = true }
 
+fix-abstract-vm = { path = "../fix-abstract-vm" }
+fix-builtins = { path = "../fix-builtins" }
 fix-common = { path = "../fix-common" }
 fix-codegen = { path = "../fix-codegen" }
 fix-error = { path = "../fix-error" }

fix/src/lib.rs

@@ -2,39 +2,45 @@
 #![allow(dead_code)]
 
 use bumpalo::Bump;
+use fix_abstract_vm::{ForceMode, StaticValue, VmCode, VmContext, VmRuntimeCtx};
+use fix_builtins::PrimOpPhase;
 use fix_codegen::disassembler::{Disassembler, DisassemblerContext};
-use fix_codegen::{BytecodeContext, InstructionPtr};
+use fix_codegen::{BytecodeContext, InstructionPtr, Op};
 use fix_common::{StringId, Symbol};
 use fix_error::{Error, Result, Source};
 use fix_ir::downgrade::{Downgrade as _, DowngradeContext};
-use fix_ir::{Ir, IrRef, MaybeThunk, RawIrRef, ThunkId};
+use fix_ir::{
-use fix_vm::{ForceMode, StaticValue, Vm, VmContext};
+    GhostMaybeThunkRef, GhostRoIrRef, GhostRoMaybeThunkRef, GhostRoRef, Ir, MaybeThunk, RawIrRef,
+    ThunkId,
+};
+use fix_vm::Vm;
 use ghost_cell::{GhostCell, GhostToken};
 use hashbrown::{HashMap, HashSet};
 use string_interner::{DefaultStringInterner, Symbol as _};
 
-// mod fetcher;
-// mod nar;
-// mod nix_utils;
-// mod store;
-// mod string_context;
 mod derivation;
 pub mod logging;
 
 #[global_allocator]
 static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc;
 
+pub struct RuntimeState {
+    pub strings: DefaultStringInterner,
+    pub constants: Constants,
+}
+
+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>,
+    pub current_scope_slot: Option<u32>,
+}
+
 pub struct Evaluator {
-    bytecode: Vec<u8>,
+    pub runtime: RuntimeState,
-    constants: Constants,
+    pub code: CodeState,
-    strings: DefaultStringInterner,
-
-    sources: Vec<Source>,
-    spans: Vec<(usize, rnix::TextRange)>,
-    // FIXME: remove?
-    thunk_count: usize,
-
-    global_env: HashMap<StringId, Ir<'static, RawIrRef<'static>>>,
 }
 
 impl Default for Evaluator {
@@ -47,15 +53,24 @@ impl Evaluator {
     pub fn new() -> Self {
         let mut strings = DefaultStringInterner::new();
         let global_env = fix_ir::new_global_env(&mut 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 {
+            runtime: RuntimeState {
+                strings,
+                constants: Constants::default(),
+            },
+            code: CodeState {
                 sources: Vec::new(),
                 spans: Vec::new(),
-            strings,
                 thunk_count: 0,
-            bytecode: Vec::new(),
+                bytecode,
-            constants: Constants::default(),
-
                 global_env,
+                current_scope_slot: None,
+            },
         }
     }
 
@@ -76,19 +91,23 @@ impl Evaluator {
         source: Source,
         scope: &HashSet<StringId>,
     ) -> Result<fix_common::Value> {
-        self.do_eval(source, Some(Scope::Repl(scope)), ForceMode::Shallow)
+        self.do_eval(source, Some(ExtraScope::Repl(scope)), ForceMode::Shallow)
     }
 
     fn do_eval<'ctx>(
         &'ctx mut self,
         source: Source,
-        extra_scope: Option<Scope<'ctx>>,
+        extra_scope: Option<ExtraScope<'ctx>>,
         force_mode: ForceMode,
     ) -> Result<fix_common::Value> {
-        let root = self.downgrade(source, extra_scope)?;
+        let ip = {
-        let ip = fix_codegen::compile_bytecode(root.as_ref(), self);
+            let mut compiler = CompilerCtx {
-        let vm = Vm::new(self, ip, force_mode);
+                code: &mut self.code,
-        vm.run()
+                runtime: &mut self.runtime,
+            };
+            compiler.compile_bytecode(source, extra_scope)?
+        };
+        Vm::run(self, ip, force_mode)
     }
 
     pub fn add_binding(
@@ -97,59 +116,100 @@ impl Evaluator {
         _expr: &str,
         _scope: &mut HashSet<StringId>,
     ) -> Result<fix_common::Value> {
-        todo!()
+        todo!("add_binding")
     }
 
     pub fn compile_bytecode(&mut self, source: Source) -> Result<InstructionPtr> {
-        let root = self.downgrade(source, None)?;
+        let mut compiler = CompilerCtx {
-        let ip = fix_codegen::compile_bytecode(root.as_ref(), self);
+            code: &mut self.code,
-        Ok(ip)
+            runtime: &mut self.runtime,
+        };
+        compiler.compile_bytecode(source, None)
     }
 
     pub fn disassemble_colored(&self, ip: InstructionPtr) -> String {
         Disassembler::new(ip, self).disassemble_colored()
     }
+}
 
-    fn downgrade_ctx<'a, 'bump, 'id>(
+impl VmRuntimeCtx for RuntimeState {
-        &'a mut self,
+    fn intern_string(&mut self, s: impl AsRef<str>) -> StringId {
-        bump: &'bump Bump,
+        StringId(self.strings.get_or_intern(s))
-        token: GhostToken<'id>,
+    }
-        extra_scope: Option<Scope<'a>>,
+    fn resolve_string(&self, id: StringId) -> &str {
-    ) -> DowngradeCtx<'a, 'id, 'bump> {
+        #[allow(clippy::unwrap_used)]
-        let Self {
+        self.strings.resolve(id.0).unwrap()
-            global_env,
+    }
-            sources,
+    fn get_const(&self, id: u32) -> StaticValue {
-            thunk_count,
+        #[allow(clippy::unwrap_used)]
-            strings,
+        self.constants.get(id).unwrap()
-            ..
+    }
-        } = self;
+    fn add_const(&mut self, val: StaticValue) -> u32 {
-        DowngradeCtx {
+        self.constants.insert(val)
-            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>(
+impl VmCode for CodeState {
-        &'a mut self,
+    fn bytecode(&self) -> &[u8] {
+        &self.bytecode
+    }
+    fn compile_with_scope(
+        &mut self,
         source: Source,
-        extra_scope: Option<Scope<'a>>,
+        extra_scope: Option<fix_abstract_vm::ExtraScope>,
-    ) -> Result<OwnedIr> {
+        runtime: &mut impl VmRuntimeCtx,
+    ) -> Result<InstructionPtr> {
+        let mut compiler = CompilerCtx {
+            code: self,
+            runtime,
+        };
+        let extra = extra_scope.map(|s| match s {
+            fix_abstract_vm::ExtraScope::ScopedImport { keys, slot_id } => {
+                ExtraScope::ScopedImport { keys, slot_id }
+            }
+        });
+        compiler.compile_bytecode(source, extra)
+    }
+}
+
+impl VmContext for Evaluator {
+    fn split(&mut self) -> (&mut impl VmCode, &mut impl VmRuntimeCtx) {
+        (&mut self.code, &mut self.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 prev_scope_slot = self.code.current_scope_slot;
+        self.code.current_scope_slot = match &extra_scope {
+            Some(ExtraScope::ScopedImport { slot_id, .. }) => Some(*slot_id),
+            _ => None,
+        };
+        let result = (|| -> Result<InstructionPtr> {
+            let root = self.downgrade(source, extra_scope)?;
+            let ip = fix_codegen::compile_bytecode(root.as_ref(), self);
+            Ok(ip)
+        })();
+        self.code.current_scope_slot = prev_scope_slot;
+        result
+    }
+
+    fn downgrade(&mut self, source: Source, extra_scope: Option<ExtraScope>) -> Result<OwnedIr> {
         tracing::debug!("Parsing Nix expression");
 
-        self.sources.push(source.clone());
+        self.code.sources.push(source.clone());
 
         let root = rnix::Root::parse(&source.src);
-        handle_parse_error(root.errors(), source).map_or(Ok(()), Err)?;
+        handle_parse_error(root.errors(), source.clone()).map_or(Ok(()), Err)?;
 
         tracing::debug!("Downgrading Nix expression");
         let expr = root
@@ -158,38 +218,84 @@ impl Evaluator {
             .ok_or_else(|| Error::parse_error("unexpected EOF".into()))?;
         let bump = Bump::new();
         GhostToken::new(|token| {
-            let ir = self
+            let downgrade_ctx = DowngradeCtx::new(
-                .downgrade_ctx(&bump, token, extra_scope)
+                &bump,
-                .downgrade_toplevel(expr)?;
+                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 VmContext for &mut Evaluator {
+impl<'a, R: VmRuntimeCtx> BytecodeContext for CompilerCtx<'a, R> {
-    fn intern_string(&mut self, s: impl AsRef<str>) -> StringId {
+    fn intern_string(&mut self, s: &str) -> StringId {
-        StringId(self.strings.get_or_intern(s))
+        self.runtime.intern_string(s)
-    }
-    fn resolve_string(&self, id: StringId) -> &str {
-        #[allow(clippy::unwrap_used)]
-        self.strings.resolve(id.0).unwrap()
-    }
-    fn bytecode(&self) -> &[u8] {
-        &self.bytecode
-    }
-    fn get_const(&self, id: u32) -> StaticValue {
-        #[allow(clippy::unwrap_used)]
-        self.constants.get(id).unwrap()
     }
 
-    fn compile(&mut self, _source: Source) {
+    fn register_span(&mut self, range: rnix::TextRange) -> u32 {
-        todo!();
+        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: fix_codegen::Const) -> u32 {
+        use fix_codegen::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(_) => todo!("path value type"),
+            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 current_scope_slot(&self) -> Option<u32> {
+        self.code.current_scope_slot
     }
 }
 
 #[derive(Default)]
-struct Constants {
+pub struct Constants {
     data: Vec<StaticValue>,
     dedup: HashMap<u64, u32>,
 }
@@ -237,123 +343,117 @@ fn handle_parse_error<'a>(
     None
 }
 
-struct DowngradeCtx<'ctx, 'id, 'ir> {
+struct DowngradeCtx<'ctx, 'id, 'ir, R: VmRuntimeCtx> {
     bump: &'ir Bump,
     token: GhostToken<'id>,
-    strings: &'ctx mut DefaultStringInterner,
+    runtime: &'ctx mut R,
     source: Source,
-    scopes: Vec<Scope<'ctx>>,
+    scopes: Vec<Scope<'ctx, 'id, 'ir>>,
-    with_scope_count: u32,
+    with_stack: Vec<GhostRoMaybeThunkRef<'id, 'ir>>,
     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 {
+impl<'ctx, 'id, 'ir, R: VmRuntimeCtx> DowngradeCtx<'ctx, 'id, 'ir, R> {
-    !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,
+        runtime: &'ctx mut R,
-        global: &'ctx HashMap<StringId, Ir<'static, RawIrRef<'static>>>,
+        global: &'ctx HashMap<StringId, MaybeThunk>,
-        extra_scope: Option<Scope<'ctx>>,
+        extra_scope: Option<Scope<'ctx, 'id, 'ir>>,
         thunk_count: &'ctx mut usize,
         source: Source,
     ) -> Self {
         Self {
             bump,
             token,
-            strings: symbols,
+            runtime,
             source,
             scopes: std::iter::once(Scope::Global(global))
                 .chain(extra_scope)
                 .collect(),
             thunk_count,
             arg_count: 0,
-            with_scope_count: 0,
+            with_stack: Vec::new(),
             thunk_scopes: vec![ThunkScope::new_in(bump)],
         }
     }
 }
 
-impl<'ctx: 'ir, 'id, 'ir> DowngradeContext<'id, 'ir> for DowngradeCtx<'ctx, 'id, 'ir> {
+impl<'ctx: 'ir, 'id, 'ir, R: VmRuntimeCtx> DowngradeContext<'id, 'ir>
-    fn new_expr(&self, expr: Ir<'ir, IrRef<'id, 'ir>>) -> IrRef<'id, 'ir> {
+    for DowngradeCtx<'ctx, 'id, 'ir, R>
-        IrRef::new(self.bump.alloc(GhostCell::new(expr)))
+{
+    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: IrRef<'id, 'ir>) -> MaybeThunk {
+    fn maybe_thunk(&mut self, ir: GhostRoIrRef<'id, 'ir>) -> GhostRoMaybeThunkRef<'id, 'ir> {
         use MaybeThunk::*;
-        match *ir.borrow(&self.token) {
+        let expr = (|| {
-            Ir::Builtin(x) => return Builtin(x),
+            let expr = match *ir.borrow(&self.token) {
-            Ir::Int(x) => return Int(x),
+                Ir::Builtin(x) => Builtin(x),
-            Ir::Float(x) => return Float(x),
+                Ir::Int(x) => Int(x),
-            Ir::Bool(x) => return Bool(x),
+                Ir::Float(x) => Float(x),
-            Ir::Str(x) => return Str(x),
+                Ir::Bool(x) => Bool(x),
-            Ir::Thunk(x) => return Thunk(x),
+                Ir::Str(x) => Str(x),
-            Ir::Arg { layer } => return Arg { layer },
+                Ir::Arg { layer } => Arg { layer },
-            Ir::Builtins => return Builtins,
+                Ir::Builtins => Builtins,
-            Ir::Null => return Null,
+                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.token);
+            .add_binding(id, ir);
-        Thunk(id)
+        self.bump.alloc(GhostCell::new(Thunk(id)).into())
     }
 
     fn intern_string(&mut self, sym: impl AsRef<str>) -> StringId {
-        StringId(self.strings.get_or_intern(sym))
+        self.runtime.intern_string(sym)
     }
 
     fn resolve_sym(&self, id: StringId) -> Symbol<'_> {
-        self.strings.resolve(id.0).expect("no symbol found").into()
+        self.runtime.resolve_string(id).into()
     }
 
-    fn lookup(&self, sym: StringId, span: rnix::TextRange) -> Result<MaybeThunk> {
+    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) => {
-                    use MaybeThunk::*;
                     if let Some(expr) = global_scope.get(&sym) {
-                        let val = match expr {
+                        return Ok(expr.into());
-                            Ir::Builtins => Builtins,
-                            Ir::Builtin(s) => Builtin(*s),
-                            Ir::Bool(b) => Bool(*b),
-                            Ir::Null => Null,
-                            _ => unreachable!("globals should only contain leaf IR nodes"),
-                        };
-                        return Ok(val);
                     }
                 }
                 &Scope::Repl(repl_bindings) => {
                     if repl_bindings.contains(&sym) {
-                        return Ok(MaybeThunk::ReplBinding(sym));
+                        return Ok(self
+                            .bump
+                            .alloc(GhostCell::new(MaybeThunk::ReplBinding(sym)).into()));
                     }
                 }
-                Scope::ScopedImport(scoped_bindings) => {
+                Scope::ScopedImport { keys, .. } => {
-                    if scoped_bindings.contains(&sym) {
+                    if keys.contains(&sym) {
-                        return Ok(MaybeThunk::ScopedImportBinding(sym));
+                        return Ok(self
+                            .bump
+                            .alloc(GhostCell::new(MaybeThunk::ScopedImportBinding(sym)).into()));
                     }
                 }
                 Scope::Let(let_scope) => {
                     if let Some(&expr) = let_scope.get(&sym) {
-                        return Ok(MaybeThunk::Thunk(expr));
+                        return Ok(expr.into());
                     }
                 }
                 &Scope::Param {
@@ -361,16 +461,33 @@ impl<'ctx: 'ir, 'id, 'ir> DowngradeContext<'id, 'ir> for DowngradeCtx<'ctx, 'id,
                     abs_layer,
                 } => {
                     if param_sym == sym {
-                        return Ok(MaybeThunk::Arg {
+                        let layers: u8 =
-                            layer: self.thunk_scopes.len() - abs_layer,
+                            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_scope_count > 0 {
+        if !self.with_stack.is_empty() {
-            Ok(MaybeThunk::WithLookup(sym))
+            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)),
@@ -384,62 +501,80 @@ impl<'ctx: 'ir, 'id, 'ir> DowngradeContext<'id, 'ir> for DowngradeCtx<'ctx, 'id,
         self.source.clone()
     }
 
-    fn with_let_scope<F, R>(&mut self, keys: &[StringId], f: F) -> Result<R>
+    fn with_let_scope<F, Ret>(&mut self, keys: &[StringId], f: F) -> Result<Ret>
     where
-        F: FnOnce(&mut Self) -> Result<(bumpalo::collections::Vec<'ir, IrRef<'id, 'ir>>, R)>,
+        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 iter = keys
+        let handles = (base..base + keys.len())
-            .iter()
+            .map(|id| {
-            .enumerate()
+                &*self
-            .map(|(offset, &key)| (key, ThunkId(base + offset)));
+                    .bump
-        self.scopes.push(Scope::Let(iter.collect()));
+                    .alloc(GhostCell::new(MaybeThunk::Thunk(ThunkId(id))))
-        let (vals, ret) = {
+            })
-            let mut guard = ScopeGuard { ctx: self };
+            .collect::<Vec<_>>();
-            f(guard.as_ctx())?
+        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");
-        scope.extend_bindings((base..base + keys.len()).map(ThunkId).zip(vals));
+        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, R>(&mut self, sym: StringId, f: F) -> R
+    fn with_param_scope<F, Ret>(&mut self, sym: StringId, f: F) -> Ret
     where
-        F: FnOnce(&mut Self) -> R,
+        F: FnOnce(&mut Self) -> Ret,
     {
         self.scopes.push(Scope::Param {
             sym,
-            abs_layer: self.thunk_scopes.len(),
+            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, R>(&mut self, f: F) -> R
+    fn with_with_scope<F, Ret>(&mut self, namespace: GhostRoMaybeThunkRef<'id, 'ir>, f: F) -> Ret
     where
-        F: FnOnce(&mut Self) -> R,
+        F: FnOnce(&mut Self) -> Ret,
     {
-        self.with_scope_count += 1;
+        self.with_stack.push(namespace);
         let ret = f(self);
-        self.with_scope_count -= 1;
+        self.with_stack.pop();
         ret
     }
 
-    fn with_thunk_scope<F, R>(
+    fn with_thunk_scope<F, Ret>(
         &mut self,
         f: F,
     ) -> (
-        R,
+        Ret,
-        bumpalo::collections::Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>,
+        bumpalo::collections::Vec<'ir, (ThunkId, GhostRoIrRef<'id, 'ir>)>,
     )
     where
-        F: FnOnce(&mut Self) -> R,
+        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);
         (
@@ -456,7 +591,7 @@ impl<'ctx: 'ir, 'id, 'ir> DowngradeContext<'id, 'ir> for DowngradeCtx<'ctx, 'id,
     }
 }
 
-impl<'id, 'ir, 'ctx: 'ir> DowngradeCtx<'ctx, 'id, 'ir> {
+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
@@ -464,13 +599,15 @@ impl<'id, 'ir, 'ctx: 'ir> DowngradeCtx<'ctx, 'id, 'ir> {
             .pop()
             .expect("no thunk scope left???")
             .bindings;
-        let ir = IrRef::alloc(self.bump, Ir::TopLevel { body, thunks });
+        Ok(Ir::freeze(
-        Ok(ir.freeze(self.token))
+            self.new_expr(Ir::TopLevel { body, thunks }),
+            self.token,
+        ))
     }
 }
 
 struct ThunkScope<'id, 'ir> {
-    bindings: bumpalo::collections::Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>,
+    bindings: bumpalo::collections::Vec<'ir, (ThunkId, GhostRoIrRef<'id, 'ir>)>,
 }
 
 impl<'id, 'ir> ThunkScope<'id, 'ir> {
@@ -480,35 +617,62 @@ impl<'id, 'ir> ThunkScope<'id, 'ir> {
         }
     }
 
-    fn add_binding(&mut self, id: ThunkId, ir: IrRef<'id, 'ir>, _token: &GhostToken<'id>) {
+    fn add_binding(&mut self, id: ThunkId, ir: GhostRoIrRef<'id, 'ir>) {
         self.bindings.push((id, ir));
     }
 
-    fn extend_bindings(&mut self, iter: impl IntoIterator<Item = (ThunkId, IrRef<'id, 'ir>)>) {
+    fn extend_bindings(
+        &mut self,
+        iter: impl IntoIterator<Item = (ThunkId, GhostRoIrRef<'id, 'ir>)>,
+    ) {
         self.bindings.extend(iter);
     }
 }
 
-enum Scope<'ctx> {
+enum Scope<'ctx, 'id, 'ir> {
-    Global(&'ctx HashMap<StringId, Ir<'static, RawIrRef<'static>>>),
+    Global(&'ctx HashMap<StringId, MaybeThunk>),
     Repl(&'ctx HashSet<StringId>),
-    ScopedImport(HashSet<StringId>),
+    ScopedImport {
-    Let(HashMap<StringId, ThunkId>),
+        keys: HashSet<StringId>,
-    Param { sym: StringId, abs_layer: usize },
+        slot_id: u32,
+    },
+    Let(HashMap<StringId, GhostMaybeThunkRef<'id, 'ir>>),
+    Param {
+        sym: StringId,
+        abs_layer: u8,
+    },
 }
 
-struct ScopeGuard<'a, 'ctx, 'id, 'ir> {
+pub enum ExtraScope<'ctx> {
-    ctx: &'a mut DowngradeCtx<'ctx, 'id, 'ir>,
+    Repl(&'ctx HashSet<StringId>),
+    ScopedImport {
+        keys: HashSet<StringId>,
+        slot_id: u32,
+    },
 }
 
-impl Drop for ScopeGuard<'_, '_, '_, '_> {
+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<'id, 'ir, 'ctx> ScopeGuard<'_, 'ctx, 'id, 'ir> {
+impl<'a, 'ctx, 'id, 'ir, R: VmRuntimeCtx> ScopeGuard<'a, 'ctx, 'id, 'ir, R> {
-    fn as_ctx(&mut self) -> &mut DowngradeCtx<'ctx, 'id, 'ir> {
+    fn as_ctx(&mut self) -> &mut DowngradeCtx<'ctx, 'id, 'ir, R> {
         self.ctx
     }
 }
@@ -520,66 +684,41 @@ struct OwnedIr {
 
 impl OwnedIr {
     /// # Safety
-    ///
+    /// `ir` must be an allocation backed by `bump`. The reference's
-    /// `ir` must be allocated from `bump`.
+    /// lifetime is extended to `'static` as a placeholder; the stored IR
+    /// must only be re-borrowed via [`OwnedIr::as_ref`], which narrows
+    /// the lifetime back to that of the `&self` borrow. Moving `bump`
+    /// into the struct keeps the underlying allocation live for the
+    /// lifetime of the `OwnedIr`.
     unsafe fn new(ir: RawIrRef<'_>, bump: Bump) -> Self {
         Self {
             _bump: bump,
+            // SAFETY: see function docs - caller guarantees `ir` is in `bump`,
+            // and the `'static` lifetime is a placeholder narrowed by `as_ref`.
             ir: unsafe { std::mem::transmute::<RawIrRef<'_>, RawIrRef<'static>>(ir) },
         }
     }
 
-    fn as_ref(&self) -> RawIrRef<'_> {
+    fn as_ref<'ir>(&'ir self) -> RawIrRef<'ir> {
-        self.ir
+        // SAFETY: narrows the placeholder `'static` lifetime stored in
-    }
+        // `self.ir` down to `'ir = &'ir self`. Lifetime shortening is
-}
+        // logically sound for covariant positions; the transmute is only
-
+        // needed because `RawRef<'ir>` carries `'ir` through a GAT
-impl BytecodeContext for Evaluator {
+        // (`Ref::Ref<T>`), which prevents the compiler from inferring
-    fn intern_string(&mut self, s: &str) -> StringId {
+        // covariance automatically. The bump arena that backs the IR is
-        StringId(self.strings.get_or_intern(s))
+        // owned by `self._bump`, so the data is live for at least `'ir`.
-    }
+        unsafe { std::mem::transmute::<RawIrRef<'static>, RawIrRef<'ir>>(self.ir) }
-
-    fn register_span(&mut self, range: rnix::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: fix_codegen::Const) -> u32 {
-        use fix_codegen::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),
-            PrimOp { id, arity } => StaticValue::new_primop(id, arity),
-            Null => StaticValue::default(),
-        };
-        self.constants.insert(val)
     }
 }
 
 impl DisassemblerContext for Evaluator {
     fn get_code(&self) -> &[u8] {
-        &self.bytecode
+        &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.strings.resolve(id).unwrap()
+        self.runtime.strings.resolve(id).unwrap()
     }
 }

fix/src/main.rs

@@ -87,7 +87,7 @@ fn run_repl(eval: &mut Evaluator) -> Result<()> {
     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() {

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))
-}

flake.lock

@@ -1,5 +1,64 @@
 {
   "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": 1778445566,
+        "narHash": "sha256-oQvcadh2BCkrog+SGrG6YffKJrveYpjj3TdQJWaKhaM=",
+        "owner": "nix-community",
+        "repo": "bun2nix",
+        "rev": "2499dedd70744dba1815875b854818a3019e9e4c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "ref": "staging-2.1.0",
+        "repo": "bun2nix",
+        "type": "github"
+      }
+    },
     "fenix": {
       "inputs": {
         "nixpkgs": [
@@ -8,11 +67,11 @@
         "rust-analyzer-src": "rust-analyzer-src"
       },
       "locked": {
-        "lastModified": 1775807984,
+        "lastModified": 1778919578,
-        "narHash": "sha256-Redoe3D9zGN5I9QPHWL9vfMVQBehY1fKsMiRXQ83X3w=",
+        "narHash": "sha256-+z+jgTly48gsAiX8rOe/vs8C/2G4vdCpcEtqMJUpFqw=",
         "owner": "nix-community",
         "repo": "fenix",
-        "rev": "fcf90c0c4d368b2ca917a7afa6d08e98a397e5fd",
+        "rev": "ecd6d4ff22cfdb1339b2915455a2ff4dc85bf52e",
         "type": "github"
       },
       "original": {
@@ -24,24 +83,70 @@
     "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": 1778929997,
+        "narHash": "sha256-iAfbBUHBbR0N4DFqFWr4Jtmpc1YcOK7kpVM4f0MK1V8=",
+        "owner": "numtide",
+        "repo": "llm-agents.nix",
+        "rev": "0da8f0313c9f68c155e0932f880fc1913e7be846",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "llm-agents.nix",
+        "type": "github"
+      }
+    },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1775710090,
+        "lastModified": 1778443072,
-        "narHash": "sha256-ar3rofg+awPB8QXDaFJhJ2jJhu+KqN/PRCXeyuXR76E=",
+        "narHash": "sha256-zi7/fsqM/kFdNuED//4WOCUtezGtKKqRNORjMvfwjnA=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "4c1018dae018162ec878d42fec712642d214fdfa",
+        "rev": "da5ad661ba4e5ef59ba743f0d112cbc30e474f32",
         "type": "github"
       },
       "original": {
@@ -55,17 +160,18 @@
       "inputs": {
         "fenix": "fenix",
         "flake-compat": "flake-compat",
+        "llm-agents": "llm-agents",
         "nixpkgs": "nixpkgs"
       }
     },
     "rust-analyzer-src": {
       "flake": false,
       "locked": {
-        "lastModified": 1775745684,
+        "lastModified": 1778854817,
-        "narHash": "sha256-8MbfLwd60FNa8dRFkjE+G3TT/x21G3Rsplm1bMBQUtU=",
+        "narHash": "sha256-iG+VuMy8W585geVVCUd7pR025WsY3ZkgSv5Yt5bxDmQ=",
         "owner": "rust-lang",
         "repo": "rust-analyzer",
-        "rev": "64ddb549bc9a70d011328746fa46a8883f937b6b",
+        "rev": "1a68212c5683555ad80f0eab71db9715c6d52145",
         "type": "github"
       },
       "original": {
@@ -74,6 +180,42 @@
         "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": 1775636079,
+        "narHash": "sha256-pc20NRoMdiar8oPQceQT47UUZMBTiMdUuWrYu2obUP0=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "790751ff7fd3801feeaf96d7dc416a8d581265ba",
+        "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; [
@@ -30,12 +42,16 @@
               cargo-bloat
               lldb
               valgrind
+              kdePackages.kcachegrind
               hyperfine
               just
               samply
               tokei
 
-              claude-code
+              llm-agents.codex
+              llm-agents.claude-code
+              llm-agents.opencode
+              llm-agents.forge
             ];
           };
         }