STW

.gitignore

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

.lazy.lua

@@ -17,7 +17,7 @@ vim.lsp.config("rust_analyzer", {
     ["rust-analyzer"] = {
       cargo = {
         features = {
-          "inspector"
+          "tailcall"
         }
       }
     }

Cargo.toml

@@ -1,10 +1,42 @@
 [workspace]
 resolver = "3"
 members = [
-    "nix-js",
+    "fix",
-    "nix-js-macros"
+    "fix-abstract-vm",
+    "fix-builtins",
+    "fix-codegen",
+    "fix-common",
+    "fix-error",
+    "fix-ir",
+    "fix-primops",
+    "fix-vm",
 ]
 
 [profile.profiling]
 inherits = "release"
 debug = true
+
+[profile.lto]
+inherits = "release"
+lto = true
+
+[workspace.dependencies]
+bumpalo = { version = "3.20", features = [
+    "allocator-api2",
+    "boxed",
+    "collections",
+] }
+ghost-cell = "0.2"
+hashbrown = "0.16"
+num_enum = "0.7.5"
+smallvec = { version = "1.15", features = ["const_new", "const_generics"] }
+ere = "0.2"
+string-interner = "0.19"
+rnix = "0.14"
+rowan = "0.16"
+likely_stable = "0.1"
+
+[workspace.dependencies.gc-arena]
+git = "https://github.com/kyren/gc-arena"
+rev = "75671ae03f53718357b741ed4027560f14e90836"
+features = ["allocator-api2", "hashbrown", "smallvec"]

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

@@ -0,0 +1,502 @@
+#![allow(dead_code)]
+
+use std::fmt;
+use std::num::NonZeroU8;
+
+use sptr::Strict;
+
+const SIGN_MASK: u64 = 0x7FFF_FFFF_FFFF_FFFF;
+const QUIET_NAN: u64 = 0x7FF8_0000_0000_0000;
+const NEG_QUIET_NAN: u64 = 0xFFF8_0000_0000_0000;
+
+pub(crate) trait ArrayExt<const LEN: usize> {
+    type Elem;
+    fn truncate_to<const M: usize>(self) -> [Self::Elem; M];
+}
+
+impl<T: Default + Copy, const N: usize> ArrayExt<N> for [T; N] {
+    type Elem = T;
+    fn truncate_to<const M: usize>(self) -> [Self::Elem; M] {
+        let copy_len = usize::min(N, M);
+        let mut out = [T::default(); M];
+        out[0..copy_len].copy_from_slice(&self[0..copy_len]);
+        out
+    }
+}
+
+pub trait RawStore: Sized {
+    fn to_val(self, value: &mut Value);
+    fn from_val(value: &Value) -> Self;
+}
+
+impl RawStore for [u8; 6] {
+    #[inline]
+    fn to_val(self, value: &mut Value) {
+        value.set_data(self);
+    }
+
+    #[inline]
+    fn from_val(value: &Value) -> Self {
+        *value.data()
+    }
+}
+
+impl RawStore for bool {
+    #[inline]
+    fn to_val(self, value: &mut Value) {
+        value.set_data([u8::from(self)].truncate_to());
+    }
+
+    #[inline]
+    fn from_val(value: &Value) -> Self {
+        value.data()[0] == 1
+    }
+}
+
+macro_rules! int_store {
+    ($ty:ty) => {
+        impl RawStore for $ty {
+            #[inline]
+            fn to_val(self, value: &mut Value) {
+                let bytes = self.to_ne_bytes();
+                value.set_data(bytes.truncate_to());
+            }
+
+            #[inline]
+            fn from_val(value: &Value) -> Self {
+                <$ty>::from_ne_bytes(value.data().truncate_to())
+            }
+        }
+    };
+}
+
+int_store!(u8);
+int_store!(u16);
+int_store!(u32);
+
+int_store!(i8);
+int_store!(i16);
+int_store!(i32);
+
+fn store_ptr<P: Strict + Copy>(value: &mut Value, ptr: P) {
+    #[cfg(target_pointer_width = "64")]
+    {
+        assert!(
+            ptr.addr() <= 0x0000_FFFF_FFFF_FFFF,
+            "Pointer too large to store in NaN box"
+        );
+
+        let val = (unsafe { value.whole_mut() } as *mut [u8; 8]).cast::<P>();
+
+        let ptr = Strict::map_addr(ptr, |addr| {
+            addr | (usize::from(value.header().into_raw()) << 48)
+        });
+
+        unsafe { val.write(ptr) };
+    }
+
+    #[cfg(target_pointer_width = "32")]
+    {
+        let _ = (value, ptr);
+        unimplemented!("32-bit pointer storage not supported");
+    }
+}
+
+fn load_ptr<P: Strict>(value: &Value) -> P {
+    #[cfg(target_pointer_width = "64")]
+    {
+        let val = (unsafe { value.whole() } as *const [u8; 8]).cast::<P>();
+        let ptr = unsafe { val.read() };
+        Strict::map_addr(ptr, |addr| addr & 0x0000_FFFF_FFFF_FFFF)
+    }
+
+    #[cfg(target_pointer_width = "32")]
+    {
+        let _ = value;
+        unimplemented!("32-bit pointer storage not supported");
+    }
+}
+
+impl<T> RawStore for *const T {
+    fn to_val(self, value: &mut Value) {
+        store_ptr::<*const T>(value, self);
+    }
+
+    fn from_val(value: &Value) -> Self {
+        load_ptr::<*const T>(value)
+    }
+}
+
+impl<T> RawStore for *mut T {
+    fn to_val(self, value: &mut Value) {
+        store_ptr::<*mut T>(value, self);
+    }
+
+    fn from_val(value: &Value) -> Self {
+        load_ptr::<*mut T>(value)
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq)]
+enum TagVal {
+    _P1,
+    _P2,
+    _P3,
+    _P4,
+    _P5,
+    _P6,
+    _P7,
+
+    _N1,
+    _N2,
+    _N3,
+    _N4,
+    _N5,
+    _N6,
+    _N7,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq)]
+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 {
+        unsafe { Self::new_unchecked(neg, val.get() & 0x07) }
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) fn new_checked(neg: bool, val: u8) -> Option<RawTag> {
+        Some(RawTag(match (neg, val) {
+            (false, 1) => TagVal::_P1,
+            (false, 2) => TagVal::_P2,
+            (false, 3) => TagVal::_P3,
+            (false, 4) => TagVal::_P4,
+            (false, 5) => TagVal::_P5,
+            (false, 6) => TagVal::_P6,
+            (false, 7) => TagVal::_P7,
+
+            (true, 1) => TagVal::_N1,
+            (true, 2) => TagVal::_N2,
+            (true, 3) => TagVal::_N3,
+            (true, 4) => TagVal::_N4,
+            (true, 5) => TagVal::_N5,
+            (true, 6) => TagVal::_N6,
+            (true, 7) => TagVal::_N7,
+
+            _ => return None,
+        }))
+    }
+
+    /// # Safety
+    ///
+    /// `val` must be in the range `1..8`
+    #[inline]
+    #[must_use]
+    pub(crate) const unsafe fn new_unchecked(neg: bool, val: u8) -> RawTag {
+        RawTag(match (neg, val) {
+            (false, 1) => TagVal::_P1,
+            (false, 2) => TagVal::_P2,
+            (false, 3) => TagVal::_P3,
+            (false, 4) => TagVal::_P4,
+            (false, 5) => TagVal::_P5,
+            (false, 6) => TagVal::_P6,
+            (false, 7) => TagVal::_P7,
+
+            (true, 1) => TagVal::_N1,
+            (true, 2) => TagVal::_N2,
+            (true, 3) => TagVal::_N3,
+            (true, 4) => TagVal::_N4,
+            (true, 5) => TagVal::_N5,
+            (true, 6) => TagVal::_N6,
+            (true, 7) => TagVal::_N7,
+
+            _ => unsafe { core::hint::unreachable_unchecked() },
+        })
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) fn is_neg(self) -> bool {
+        matches!(self.0, |TagVal::_N1| TagVal::_N2
+            | TagVal::_N3
+            | TagVal::_N4
+            | TagVal::_N5
+            | TagVal::_N6
+            | TagVal::_N7)
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) fn val(self) -> NonZeroU8 {
+        match self.0 {
+            TagVal::_P1 | TagVal::_N1 => NonZeroU8::MIN,
+            TagVal::_P2 | TagVal::_N2 => NonZeroU8::MIN.saturating_add(1),
+            TagVal::_P3 | TagVal::_N3 => NonZeroU8::MIN.saturating_add(2),
+            TagVal::_P4 | TagVal::_N4 => NonZeroU8::MIN.saturating_add(3),
+            TagVal::_P5 | TagVal::_N5 => NonZeroU8::MIN.saturating_add(4),
+            TagVal::_P6 | TagVal::_N6 => NonZeroU8::MIN.saturating_add(5),
+            TagVal::_P7 | TagVal::_N7 => NonZeroU8::MIN.saturating_add(6),
+        }
+    }
+
+    #[inline]
+    #[must_use]
+    pub const fn neg_val(self) -> (bool, u8) {
+        match self.0 {
+            TagVal::_P1 => (false, 1),
+            TagVal::_P2 => (false, 2),
+            TagVal::_P3 => (false, 3),
+            TagVal::_P4 => (false, 4),
+            TagVal::_P5 => (false, 5),
+            TagVal::_P6 => (false, 6),
+            TagVal::_P7 => (false, 7),
+            TagVal::_N1 => (true, 1),
+            TagVal::_N2 => (true, 2),
+            TagVal::_N3 => (true, 3),
+            TagVal::_N4 => (true, 4),
+            TagVal::_N5 => (true, 5),
+            TagVal::_N6 => (true, 6),
+            TagVal::_N7 => (true, 7),
+        }
+    }
+}
+
+impl fmt::Debug for RawTag {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RawTag")
+            .field("neg", &self.is_neg())
+            .field("val", &self.val())
+            .finish()
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+#[repr(transparent)]
+struct Header(u16);
+
+impl Header {
+    #[inline]
+    fn new(tag: RawTag) -> Header {
+        let (neg, val) = tag.neg_val();
+        Header(0x7FF8 | (u16::from(neg) << 15) | u16::from(val))
+    }
+
+    #[inline]
+    const fn tag(self) -> RawTag {
+        unsafe { RawTag::new_unchecked(self.get_sign(), self.get_tag()) }
+    }
+
+    #[inline]
+    const fn get_sign(self) -> bool {
+        self.0 & 0x8000 != 0
+    }
+
+    #[inline]
+    const fn get_tag(self) -> u8 {
+        (self.0 & 0x0007) as u8
+    }
+
+    #[inline]
+    fn into_raw(self) -> u16 {
+        self.0
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+#[repr(C, align(8))]
+pub struct Value {
+    #[cfg(target_endian = "big")]
+    header: Header,
+    data: [u8; 6],
+    #[cfg(target_endian = "little")]
+    header: Header,
+}
+
+impl Value {
+    #[inline]
+    pub(crate) fn new(tag: RawTag, data: [u8; 6]) -> Value {
+        Value {
+            header: Header::new(tag),
+            data,
+        }
+    }
+
+    #[inline]
+    pub(crate) fn empty(tag: RawTag) -> Value {
+        Value::new(tag, [0; 6])
+    }
+
+    pub(crate) fn store<T: RawStore>(tag: RawTag, val: T) -> Value {
+        let mut v = Value::new(tag, [0; 6]);
+        T::to_val(val, &mut v);
+        v
+    }
+
+    pub(crate) fn load<T: RawStore>(self) -> T {
+        T::from_val(&self)
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) const fn tag(&self) -> RawTag {
+        self.header.tag()
+    }
+
+    #[inline]
+    fn header(&self) -> &Header {
+        &self.header
+    }
+
+    #[inline]
+    pub(crate) fn set_data(&mut self, val: [u8; 6]) {
+        self.data = val;
+    }
+
+    #[inline]
+    #[must_use]
+    pub fn data(&self) -> &[u8; 6] {
+        &self.data
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) fn data_mut(&mut self) -> &mut [u8; 6] {
+        &mut self.data
+    }
+
+    #[inline]
+    #[must_use]
+    unsafe fn whole(&self) -> &[u8; 8] {
+        let ptr = (self as *const Value).cast::<[u8; 8]>();
+        unsafe { &*ptr }
+    }
+
+    #[inline]
+    #[must_use]
+    unsafe fn whole_mut(&mut self) -> &mut [u8; 8] {
+        let ptr = (self as *mut Value).cast::<[u8; 8]>();
+        unsafe { &mut *ptr }
+    }
+}
+
+#[repr(C)]
+#[derive(Copy, Clone)]
+pub(crate) union RawBox {
+    float: f64,
+    value: Value,
+    bits: u64,
+    #[cfg(target_pointer_width = "64")]
+    ptr: *const (),
+    #[cfg(target_pointer_width = "32")]
+    ptr: (u32, *const ()),
+}
+
+impl RawBox {
+    #[inline]
+    #[must_use]
+    pub(crate) fn from_float(val: f64) -> RawBox {
+        match (val.is_nan(), val.is_sign_positive()) {
+            (true, true) => RawBox {
+                float: f64::from_bits(QUIET_NAN),
+            },
+            (true, false) => RawBox {
+                float: f64::from_bits(NEG_QUIET_NAN),
+            },
+            (false, _) => RawBox { float: val },
+        }
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) fn from_value(value: Value) -> RawBox {
+        RawBox { value }
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) const fn tag(&self) -> Option<RawTag> {
+        if self.is_value() {
+            Some(unsafe { self.value.tag() })
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) fn is_float(&self) -> bool {
+        (unsafe { !self.float.is_nan() } || unsafe { self.bits & SIGN_MASK == QUIET_NAN })
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) const fn is_value(&self) -> bool {
+        (unsafe { self.float.is_nan() } && unsafe { self.bits & SIGN_MASK != QUIET_NAN })
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) fn float(&self) -> Option<&f64> {
+        if self.is_float() {
+            Some(unsafe { &self.float })
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) fn value(&self) -> Option<&Value> {
+        if self.is_value() {
+            Some(unsafe { &self.value })
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    pub(crate) fn into_float_unchecked(self) -> f64 {
+        unsafe { self.float }
+    }
+
+    #[inline]
+    #[must_use]
+    pub(crate) fn to_bits(self) -> u64 {
+        unsafe { self.bits }
+    }
+}
+
+impl fmt::Debug for RawBox {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.float() {
+            Some(val) => f.debug_tuple("RawBox::Float").field(val).finish(),
+            None => {
+                let val = self.value().expect("RawBox is neither float nor value");
+
+                f.debug_struct("RawBox::Data")
+                    .field("tag", &val.tag())
+                    .field("data", val.data())
+                    .finish()
+            }
+        }
+    }
+}

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

@@ -0,0 +1,728 @@
+#![allow(dead_code)]
+
+use std::cell::RefCell;
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem::size_of;
+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;
+use smallvec::SmallVec;
+use string_interner::Symbol;
+use string_interner::symbol::SymbolU32;
+
+use crate::boxing::{RawBox, RawStore, RawTag, Value as RawValue};
+use crate::string_context::StringContext;
+
+mod private {
+    pub trait Cealed {}
+}
+
+/// # Safety
+///
+/// TAG must be unique among all implementors.
+#[allow(private_interfaces)]
+pub unsafe trait Storable: private::Cealed {
+    const TAG: RawTag;
+}
+#[allow(private_bounds)]
+pub trait InlineStorable: Storable + RawStore {}
+pub trait GcStorable: Storable {}
+
+macro_rules! define_value_types {
+    (
+        inline { $($itype:ty => $itag:expr, $iname:literal;)* }
+        gc { $($gtype:ty => $gtag:expr, $gname:literal;)* }
+    ) => {
+        $(
+        #[allow(private_interfaces)]
+        unsafe impl Storable for $itype {
+            const TAG: RawTag = $itag;
+        }
+        impl InlineStorable for $itype {}
+        impl private::Cealed for $itype {}
+        )*
+        $(
+        #[allow(private_interfaces)]
+        unsafe impl Storable for $gtype {
+            const TAG: RawTag = $gtag;
+        }
+        impl GcStorable for $gtype {}
+        impl private::Cealed for $gtype {}
+        )*
+
+        const _: () = assert!(size_of::<Value<'static>>() == 8);
+        $(const _: () = assert!(size_of::<$itype>() <= 6);)*
+
+        const _: () = {
+            let tags: &[(bool, u8)] = &[$(RawTag::neg_val($itag)),*, $(RawTag::neg_val($gtag)),*];
+            let mut mask_false: u8 = 0;
+            let mut mask_true: u8 = 0;
+            let mut i = 0;
+            while i < tags.len() {
+                let (neg, val) = tags[i];
+                let bit = 1 << val;
+                if neg {
+                    assert!(mask_true & bit == 0, "duplicate true tag id");
+                    mask_true |= bit;
+                } else {
+                    assert!(mask_false & bit == 0, "duplicate false tag id");
+                    mask_false |= bit;
+                }
+                i += 1;
+            }
+        };
+
+        unsafe impl<'gc> Collect<'gc> for Value<'gc> {
+            const NEEDS_TRACE: bool = true;
+            fn trace<T: Trace<'gc>>(&self, cc: &mut T) {
+                let Some(tag) = self.raw.tag() else { return };
+                match tag {
+                    $(<$gtype as Storable>::TAG => unsafe {
+                        self.load_gc::<$gtype>().trace(cc)
+                    },)*
+                    $(<$itype as Storable>::TAG => (),)*
+                    _ => unreachable!("invalid value tag"),
+                }
+            }
+        }
+
+        impl fmt::Debug for Value<'_> {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                match self.tag() {
+                    None => write!(f, "Float({:?})", unsafe {
+                        self.raw.float().unwrap_unchecked()
+                    }),
+                    $(Some(<$itype as Storable>::TAG) => write!(f, "{}({:?})", $iname, unsafe {
+                        self.as_inline::<$itype>().unwrap_unchecked()
+                    }),)*
+                    $(Some(<$gtype as Storable>::TAG) =>
+                        write!(f, "{}(..)", $gname),)*
+                    _ => unreachable!("invalid value tag"),
+                }
+            }
+        }
+    };
+}
+
+define_value_types! {
+    inline {
+        i32 => RawTag::P1, "SmallInt";
+        bool => RawTag::P2, "Bool";
+        Null => RawTag::P3, "Null";
+        StringId => RawTag::P4, "SmallString";
+        PrimOp => RawTag::P5, "PrimOp";
+        Path => RawTag::N6, "Path";
+    }
+    gc {
+        i64 => RawTag::P6, "BigInt";
+        NixString => RawTag::P7, "String";
+        AttrSet<'_> => RawTag::N1, "AttrSet";
+        List<'_> => RawTag::N2, "List";
+        Thunk<'_> => RawTag::N3, "Thunk";
+        Closure<'_> => RawTag::N4, "Closure";
+        PrimOpApp<'_> => RawTag::N5, "PrimOpApp";
+    }
+}
+
+/// # Nix runtime value representation
+///
+/// NaN-boxed value fitting in 8 bytes.
+#[derive(Copy, Clone)]
+#[repr(transparent)]
+pub struct Value<'gc> {
+    raw: RawBox,
+    _marker: PhantomData<Gc<'gc, ()>>,
+}
+
+impl Default for Value<'_> {
+    #[inline(always)]
+    fn default() -> Self {
+        Self::new_inline(Null)
+    }
+}
+
+impl<'gc> Value<'gc> {
+    #[inline(always)]
+    fn from_raw_value(rv: RawValue) -> Self {
+        Self {
+            raw: RawBox::from_value(rv),
+            _marker: PhantomData,
+        }
+    }
+
+    /// Load a GC pointer from a value with a negative tag.
+    ///
+    /// # Safety
+    ///
+    /// The value must actually store a `Gc<'gc, T>` with the matching type.
+    #[inline(always)]
+    unsafe fn load_gc<T: GcStorable>(self) -> Gc<'gc, T> {
+        unsafe {
+            let rv = self.raw.value().unwrap_unchecked();
+            let ptr: *const T = <*const T as RawStore>::from_val(rv);
+            Gc::from_ptr(ptr)
+        }
+    }
+
+    #[inline(always)]
+    const fn tag(self) -> Option<RawTag> {
+        self.raw.tag()
+    }
+}
+
+impl<'gc> Value<'gc> {
+    #[inline]
+    pub fn new_float(val: f64) -> Self {
+        Self {
+            raw: RawBox::from_float(val),
+            _marker: PhantomData,
+        }
+    }
+
+    #[inline]
+    pub fn new_inline<T: InlineStorable>(val: T) -> Self {
+        Self::from_raw_value(RawValue::store(T::TAG, val))
+    }
+
+    #[inline]
+    pub fn new_gc<T: GcStorable>(gc: Gc<'gc, T>) -> Self {
+        let ptr = Gc::as_ptr(gc);
+        Self::from_raw_value(RawValue::store(T::TAG, ptr))
+    }
+
+    #[inline]
+    pub fn make_int(val: i64, mc: &Mutation<'gc>) -> Self {
+        if val >= i32::MIN as i64 && val <= i32::MAX as i64 {
+            Value::new_inline(val as i32)
+        } else {
+            Value::new_gc(Gc::new(mc, val))
+        }
+    }
+}
+
+impl<'gc> Value<'gc> {
+    #[inline]
+    pub fn is_float(self) -> bool {
+        self.raw.is_float()
+    }
+
+    #[inline]
+    pub fn is<T: Storable>(self) -> bool {
+        self.tag() == Some(T::TAG)
+    }
+}
+
+impl<'gc> Value<'gc> {
+    #[inline]
+    pub fn as_float(self) -> Option<f64> {
+        self.raw.float().copied()
+    }
+
+    #[inline]
+    pub fn as_inline<T: InlineStorable>(self) -> Option<T> {
+        if self.is::<T>() {
+            Some(unsafe {
+                let rv = self.raw.value().unwrap_unchecked();
+                T::from_val(rv)
+            })
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    pub fn as_gc<T: GcStorable>(self) -> Option<Gc<'gc, T>> {
+        if self.is::<T>() {
+            Some(unsafe {
+                let rv = self.raw.value().unwrap_unchecked();
+                let ptr: *const T = <*const T as RawStore>::from_val(rv);
+                Gc::from_ptr(ptr)
+            })
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    pub fn to_bits(self) -> u64 {
+        self.raw.to_bits()
+    }
+
+    #[inline]
+    pub fn as_num(self) -> Option<NixNum> {
+        if let Some(i) = self.as_inline::<i32>() {
+            Some(NixNum::Int(i as i64))
+        } else if let Some(gc_i) = self.as_gc::<i64>() {
+            Some(NixNum::Int(*gc_i))
+        } else {
+            self.as_float().map(NixNum::Float)
+        }
+    }
+
+    #[inline]
+    pub fn restrict(self) -> Result<StrictValue<'gc>, Gc<'gc, Thunk<'gc>>> {
+        if let Some(thunk) = self.as_gc::<Thunk<'gc>>() {
+            Err(thunk)
+        } else {
+            Ok(StrictValue(self))
+        }
+    }
+
+    #[inline]
+    pub fn ty(self) -> NixType {
+        if self.is_float() {
+            NixType::Float
+        } else if self.is::<i32>() || self.is::<i64>() {
+            NixType::Int
+        } else if self.is::<bool>() {
+            NixType::Bool
+        } else if self.is::<Null>() {
+            NixType::Null
+        } else if self.is::<StringId>() {
+            NixType::String
+        } else if self.is::<PrimOp>() {
+            NixType::PrimOp
+        } else if self.is::<NixString>() {
+            NixType::String
+        } else if self.is::<Path>() {
+            NixType::Path
+        } else if self.is::<AttrSet>() {
+            NixType::AttrSet
+        } else if self.is::<List>() {
+            NixType::List
+        } else if self.is::<Thunk>() {
+            NixType::Thunk
+        } else if self.is::<Closure>() {
+            NixType::Closure
+        } else if self.is::<PrimOpApp>() {
+            NixType::PrimOpApp
+        } else {
+            unreachable!("value has no recognized type tag")
+        }
+    }
+
+    #[inline]
+    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)]
+#[repr(transparent)]
+pub struct StaticValue(Value<'static>);
+
+impl<'gc> From<StaticValue> for Value<'gc> {
+    #[inline]
+    fn from(value: StaticValue) -> Self {
+        // SAFETY: StaticValue is guaranteed to not contain any `Gc`.
+        unsafe { std::mem::transmute::<Value<'static>, Value<'gc>>(value.0) }
+    }
+}
+
+impl StaticValue {
+    #[inline]
+    pub fn new_float(val: f64) -> Self {
+        Self(Value::new_float(val))
+    }
+    #[inline]
+    pub fn new_inline<T: InlineStorable>(val: T) -> Self {
+        Self(Value::new_inline(val))
+    }
+    #[inline]
+    pub fn new_primop(id: BuiltinId, arity: u8, dispatch_ip: u32) -> Self {
+        Self(Value::new_inline(PrimOp {
+            id,
+            arity,
+            dispatch_ip,
+        }))
+    }
+    #[inline]
+    pub fn is_float(self) -> bool {
+        self.0.is_float()
+    }
+    #[inline]
+    pub fn is<T: InlineStorable>(self) -> bool {
+        self.0.is::<T>()
+    }
+    #[inline]
+    pub fn as_float(self) -> Option<f64> {
+        self.0.as_float()
+    }
+    #[inline]
+    pub fn as_inline<T: InlineStorable>(self) -> Option<T> {
+        self.0.as_inline::<T>()
+    }
+    #[inline]
+    pub fn to_bits(self) -> u64 {
+        self.0.raw.to_bits()
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub struct Null;
+impl RawStore for Null {
+    fn to_val(self, value: &mut RawValue) {
+        value.set_data([0; 6]);
+    }
+    fn from_val(_: &RawValue) -> Self {
+        Self
+    }
+}
+
+impl RawStore for StringId {
+    fn to_val(self, value: &mut RawValue) {
+        (self.0.to_usize() as u32).to_val(value);
+    }
+    fn from_val(value: &RawValue) -> Self {
+        Self(
+            SymbolU32::try_from_usize(u32::from_val(value) as usize)
+                .expect("failed to read StringId from Value"),
+        )
+    }
+}
+
+/// A canonicalized absolute path. Inline value carrying an interned
+/// `StringId` whose contents are the path's absolute, dot-resolved form.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct Path(pub StringId);
+
+impl RawStore for Path {
+    fn to_val(self, value: &mut RawValue) {
+        self.0.to_val(value);
+    }
+    fn from_val(value: &RawValue) -> Self {
+        Self(StringId::from_val(value))
+    }
+}
+
+#[derive(Collect)]
+#[collect(require_static)]
+pub struct NixString {
+    data: Box<str>,
+    context: StringContext,
+}
+
+impl NixString {
+    pub fn new(s: impl Into<Box<str>>) -> Self {
+        Self {
+            data: s.into(),
+            context: StringContext::new(),
+        }
+    }
+
+    /// Construct a `NixString` whose `context` is already sorted+deduped.
+    /// The caller is responsible for invariant maintenance.
+    pub fn with_context(s: impl Into<Box<str>>, context: StringContext) -> Self {
+        Self {
+            data: s.into(),
+            context,
+        }
+    }
+
+    pub fn as_str(&self) -> &str {
+        &self.data
+    }
+
+    pub fn context(&self) -> &StringContext {
+        &self.context
+    }
+
+    pub fn has_context(&self) -> bool {
+        !self.context.is_empty()
+    }
+}
+
+impl fmt::Debug for NixString {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.data, f)
+    }
+}
+
+#[derive(Collect, Debug, Default)]
+#[collect(no_drop)]
+pub struct AttrSet<'gc> {
+    pub entries: SmallVec<[(StringId, Value<'gc>); 4]>,
+}
+
+impl<'gc> AttrSet<'gc> {
+    pub fn from_sorted_unchecked(entries: SmallVec<[(StringId, Value<'gc>); 4]>) -> Self {
+        debug_assert!(entries.is_sorted_by_key(|(key, _)| *key));
+        Self { entries }
+    }
+
+    pub fn lookup(&self, key: StringId) -> Option<Value<'gc>> {
+        self.entries
+            .binary_search_by_key(&key, |(k, _)| *k)
+            .ok()
+            .map(|i| self.entries[i].1)
+    }
+
+    pub fn has(&self, key: StringId) -> bool {
+        self.entries.binary_search_by_key(&key, |(k, _)| *k).is_ok()
+    }
+
+    pub fn merge(&self, other: &Self, mc: &Mutation<'gc>) -> Gc<'gc, Self> {
+        use std::cmp::Ordering::*;
+
+        debug_assert!(self.entries.is_sorted_by_key(|(key, _)| *key));
+        debug_assert!(other.entries.is_sorted_by_key(|(key, _)| *key));
+
+        let mut entries = SmallVec::new();
+        let mut i = 0;
+        let mut j = 0;
+        while i < self.entries.len() && j < other.entries.len() {
+            match self.entries[i].0.cmp(&other.entries[j].0) {
+                Less => {
+                    entries.push(self.entries[i]);
+                    i += 1;
+                }
+                Greater => {
+                    entries.push(other.entries[j]);
+                    j += 1;
+                }
+                Equal => {
+                    entries.push(other.entries[j]);
+                    i += 1;
+                    j += 1;
+                }
+            }
+        }
+        entries.extend(other.entries[j..].iter().cloned());
+        entries.extend(self.entries[i..].iter().cloned());
+
+        debug_assert!(entries.is_sorted_by_key(|(key, _)| *key));
+
+        Gc::new(mc, AttrSet { entries })
+    }
+}
+
+#[derive(Collect, Debug, Default)]
+#[repr(transparent)]
+#[collect(no_drop)]
+pub struct List<'gc> {
+    pub inner: RefLock<SmallVec<[Value<'gc>; 4]>>,
+}
+
+impl<'gc> List<'gc> {
+    pub fn new(mc: &Mutation<'gc>, data: SmallVec<[Value<'gc>; 4]>) -> Gc<'gc, Self> {
+        Gc::new(
+            mc,
+            Self {
+                inner: RefLock::new(data),
+            },
+        )
+    }
+
+    pub fn new_gc(mc: &Mutation<'gc>) -> Gc<'gc, Self> {
+        Gc::new(mc, Self::default())
+    }
+}
+
+impl<'gc> Unlock for List<'gc> {
+    type Unlocked = RefCell<SmallVec<[Value<'gc>; 4]>>;
+    unsafe fn unlock_unchecked(&self) -> &Self::Unlocked {
+        unsafe { self.inner.unlock_unchecked() }
+    }
+}
+
+pub type Thunk<'gc> = RefLock<ThunkState<'gc>>;
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub enum ThunkState<'gc> {
+    Pending { ip: usize, env: GcEnv<'gc> },
+    Apply { func: Value<'gc>, arg: Value<'gc> },
+    Blackhole,
+    Evaluated(StrictValue<'gc>),
+}
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub struct Env<'gc> {
+    pub locals: SmallVec<[Value<'gc>; 4]>,
+    pub prev: Option<GcEnv<'gc>>,
+}
+pub type GcEnv<'gc> = GcRefLock<'gc, Env<'gc>>;
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub struct WithEnv<'gc> {
+    pub env: Value<'gc>,
+    pub prev: Option<GcWithEnv<'gc>>,
+}
+pub type GcWithEnv<'gc> = Gc<'gc, WithEnv<'gc>>;
+
+impl<'gc> Env<'gc> {
+    pub fn empty() -> Self {
+        Env {
+            locals: SmallVec::new(),
+            prev: None,
+        }
+    }
+
+    pub fn with_arg(arg: Value<'gc>, n_locals: u32, prev: Gc<'gc, RefLock<Env<'gc>>>) -> Self {
+        let mut locals = smallvec::smallvec![Value::default(); 1 + n_locals as usize];
+        locals[0] = arg;
+        Env {
+            locals,
+            prev: Some(prev),
+        }
+    }
+}
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub struct Closure<'gc> {
+    pub ip: u32,
+    pub n_locals: u32,
+    pub env: Gc<'gc, RefLock<Env<'gc>>>,
+    pub pattern: Option<Gc<'gc, PatternInfo>>,
+}
+
+#[derive(Collect, Debug)]
+#[collect(require_static)]
+pub struct PatternInfo {
+    pub required: SmallVec<[StringId; 4]>,
+    pub optional: SmallVec<[StringId; 4]>,
+    pub ellipsis: bool,
+    pub param_spans: Box<[(StringId, u32)]>,
+}
+
+#[repr(packed, Rust)]
+#[derive(Clone, Copy, Debug, Collect)]
+#[collect(require_static)]
+pub struct PrimOp {
+    pub id: BuiltinId,
+    pub arity: u8,
+    pub dispatch_ip: u32,
+}
+
+impl RawStore for PrimOp {
+    fn to_val(self, value: &mut RawValue) {
+        let bytes = self.dispatch_ip.to_le_bytes();
+        value.set_data([
+            self.id as u8,
+            self.arity,
+            bytes[0],
+            bytes[1],
+            bytes[2],
+            bytes[3],
+        ]);
+    }
+    fn from_val(value: &RawValue) -> Self {
+        let [id, arity, bytes @ ..] = *value.data();
+        Self {
+            id: BuiltinId::try_from_primitive(id).expect("invalid BuiltinId"),
+            arity,
+            dispatch_ip: u32::from_le_bytes(bytes),
+        }
+    }
+}
+
+#[derive(Collect, Debug)]
+#[collect(no_drop)]
+pub struct PrimOpApp<'gc> {
+    pub primop: PrimOp,
+    pub arity: u8,
+    pub args: [Value<'gc>; 3],
+}
+
+#[derive(Copy, Clone, Default, Collect)]
+#[repr(transparent)]
+#[collect(no_drop)]
+pub struct StrictValue<'gc>(Value<'gc>);
+
+impl<'gc> StrictValue<'gc> {
+    #[inline]
+    pub fn relax(self) -> Value<'gc> {
+        self.0
+    }
+}
+
+impl<'gc> Deref for StrictValue<'gc> {
+    type Target = Value<'gc>;
+    #[inline]
+    fn deref(&self) -> &Value<'gc> {
+        &self.0
+    }
+}
+
+impl fmt::Debug for StrictValue<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.0, f)
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Collect)]
+#[collect(require_static)]
+pub enum NixType {
+    Int,
+    Float,
+    Bool,
+    Null,
+    String,
+    Path,
+    AttrSet,
+    List,
+    Thunk,
+    Closure,
+    PrimOp,
+    PrimOpApp,
+}
+
+impl NixType {
+    pub fn display(self) -> &'static str {
+        use NixType::*;
+        match self {
+            Int => "an integer",
+            Float => "a float",
+            Bool => "a boolean",
+            Null => "null",
+            String => "a string",
+            Path => "a path",
+            AttrSet => "a set",
+            List => "a list",
+            Thunk => "a thunk",
+            Closure => "a function",
+            PrimOp => "a built-in function",
+            PrimOpApp => "a partially applied built-in function",
+        }
+    }
+}
+
+impl std::fmt::Display for NixType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.display())
+    }
+}
+
+pub enum NixNum {
+    Int(i64),
+    Float(f64),
+}

fix-builtins/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "fix-builtins"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+num_enum = { workspace = true }
+gc-arena = { workspace = true }

fix-builtins/src/lib.rs

@@ -0,0 +1,399 @@
+use gc_arena::Collect;
+use num_enum::TryFromPrimitive;
+
+macro_rules! define_builtins {
+    ($(($name:literal, $variant:ident, $arity:expr)),* $(,)?) => {
+        /// Builtin function registry.
+        /// Array index IS the PrimOp id. (name, arity) pairs.
+        pub const BUILTINS: &[(&str, u8)] = &[
+            $(($name, $arity),)*
+        ];
+
+        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, TryFromPrimitive, Collect)]
+        #[repr(u8)]
+        #[collect(require_static)]
+        pub enum BuiltinId {
+            $($variant,)*
+        }
+    };
+}
+
+define_builtins! {
+    ("abort",                    Abort,                    1),
+    ("__add",                      Add,                      2),
+    ("__addErrorContext",          AddErrorContext,           2),
+    ("__all",                      All,                      2),
+    ("__any",                      Any,                      2),
+    ("__appendContext",            AppendContext,             2),
+    ("__attrNames",                AttrNames,                1),
+    ("__attrValues",               AttrValues,               1),
+    ("baseNameOf",               BaseNameOf,               1),
+    ("__bitAnd",                   BitAnd,                   2),
+    ("__bitOr",                    BitOr,                    2),
+    ("__bitXor",                   BitXor,                   2),
+    ("break",                    Break,                    1),
+    ("__catAttrs",                 CatAttrs,                 2),
+    ("__ceil",                     Ceil,                     1),
+    ("__compareVersions",          CompareVersions,          2),
+    ("__concatLists",              ConcatLists,              1),
+    ("__concatMap",                ConcatMap,                2),
+    ("__concatStringsSep",         ConcatStringsSep,         2),
+    ("__convertHash",              ConvertHash,              1),
+    ("__deepSeq",                  DeepSeq,                  2),
+    ("derivation",               Derivation,               1),
+    ("derivationStrict",         DerivationStrict,         1),
+    ("dirOf",                    DirOf,                    1),
+    ("__div",                      Div,                      2),
+    ("__elem",                     Elem,                     2),
+    ("__elemAt",                   ElemAt,                   2),
+    ("fetchGit",                 FetchGit,                 1),
+    ("fetchMercurial",           FetchMercurial,           1),
+    ("fetchTarball",             FetchTarball,             1),
+    ("fetchTree",                FetchTree,                1),
+    ("__fetchurl",                 FetchUrl,                 1),
+    ("__filter",                   Filter,                   2),
+    ("__filterSource",             FilterSource,             2),
+    ("__findFile",                 FindFile,                 2),
+    ("__floor",                    Floor,                    1),
+    ("__foldl'",                   FoldlStrict,              3),
+    ("__fromJSON",                 FromJSON,                 1),
+    ("fromTOML",                 FromTOML,                 1),
+    ("__functionArgs",             FunctionArgs,             1),
+    ("__genList",                  GenList,                  2),
+    ("__genericClosure",           GenericClosure,           1),
+    ("__getAttr",                  GetAttr,                  2),
+    ("__getContext",               GetContext,               1),
+    ("__getEnv",                   GetEnv,                   1),
+    ("__groupBy",                  GroupBy,                  2),
+    ("__hasAttr",                  HasAttr,                  2),
+    ("__hasContext",               HasContext,               1),
+    ("__hashFile",                 HashFile,                 2),
+    ("__hashString",               HashString,               2),
+    ("__head",                     Head,                     1),
+    ("import",                   Import,                   1),
+    ("__intersectAttrs",           IntersectAttrs,           2),
+    ("__isAttrs",                  IsAttrs,                  1),
+    ("__isBool",                   IsBool,                   1),
+    ("__isFloat",                  IsFloat,                  1),
+    ("__isFunction",               IsFunction,               1),
+    ("__isInt",                    IsInt,                    1),
+    ("__isList",                   IsList,                   1),
+    ("isNull",                   IsNull,                   1),
+    ("__isPath",                   IsPath,                   1),
+    ("__isString",                 IsString,                 1),
+    ("__length",                   Length,                   1),
+    ("__lessThan",                 LessThan,                 2),
+    ("__listToAttrs",              ListToAttrs,              1),
+    ("map",                      Map,                      2),
+    ("__mapAttrs",                 MapAttrs,                 2),
+    ("__match",                    Match,                    2),
+    ("__mul",                      Mul,                      2),
+    ("__parseDrvName",             ParseDrvName,             1),
+    ("__partition",                Partition,                2),
+    ("__path",                     Path,                     1),
+    ("__pathExists",               PathExists,               1),
+    ("placeholder",              Placeholder,              1),
+    ("__readDir",                  ReadDir,                  1),
+    ("__readFile",                 ReadFile,                 1),
+    ("__readFileType",             ReadFileType,             1),
+    ("removeAttrs",              RemoveAttrs,              2),
+    ("__replaceStrings",           ReplaceStrings,           3),
+    ("scopedImport",             ScopedImport,             2),
+    ("__seq",                      Seq,                      2),
+    ("__sort",                     Sort,                     2),
+    ("__split",                    Split,                    2),
+    ("__splitVersion",             SplitVersion,             1),
+    ("__storePath",                StorePath,                1),
+    ("__stringLength",             StringLength,             1),
+    ("__sub",                      Sub,                      2),
+    ("__substring",                Substring,                3),
+    ("__tail",                     Tail,                     1),
+    ("throw",                    Throw,                    1),
+    ("__toFile",                   ToFile,                   2),
+    ("__toJSON",                   ToJSON,                   1),
+    ("__toPath",                   ToPath,                   1),
+    ("toString",                 ToString,                 1),
+    ("__toXML",                    ToXML,                    1),
+    ("__trace",                    Trace,                    2),
+    ("__tryEval",                  TryEval,                  1),
+    ("__typeOf",                   TypeOf,                   1),
+    ("__unsafeDiscardStringContext", UnsafeDiscardStringContext, 1),
+    ("__unsafeDiscardOutputDependency", UnsafeDiscardOutputDependency, 1),
+    ("__unsafeGetAttrPos",         UnsafeGetAttrPos,         2),
+    ("__warn",                     Warn,                     2),
+    ("__zipAttrsWith",             ZipAttrsWith,             2),
+}
+
+#[repr(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/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "fix-codegen"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+hashbrown = { workspace = true }
+num_enum = { workspace = true }
+rnix = { workspace = true }
+string-interner = { workspace = true }
+colored = "3.1.1"
+
+fix-builtins = { path = "../fix-builtins" }
+fix-common = { path = "../fix-common" }
+fix-ir = { path = "../fix-ir" }

fix-codegen/src/disassembler.rs

@@ -0,0 +1,467 @@
+use std::fmt::Write;
+
+use colored::Colorize;
+use fix_builtins::BuiltinId;
+use num_enum::TryFromPrimitive;
+
+use crate::{InstructionPtr, Op, OperandType};
+
+pub trait DisassemblerContext {
+    fn resolve_string(&self, id: u32) -> &str;
+    fn get_code(&self) -> &[u8];
+}
+
+pub struct Disassembler<'a, Ctx> {
+    code: &'a [u8],
+    ctx: &'a Ctx,
+    pc: usize,
+}
+
+impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
+    pub fn new(ip: InstructionPtr, ctx: &'a Ctx) -> Self {
+        Self {
+            code: ctx.get_code(),
+            ctx,
+            pc: ip.0,
+        }
+    }
+
+    #[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()
+            .expect("no enough bytes");
+        self.pc += 2;
+        u16::from_le_bytes(bytes)
+    }
+
+    #[inline(always)]
+    fn read_u32(&mut self) -> u32 {
+        let bytes = self.code[self.pc..self.pc + 4]
+            .try_into()
+            .expect("no enough bytes");
+        self.pc += 4;
+        u32::from_le_bytes(bytes)
+    }
+
+    #[inline(always)]
+    fn read_i32(&mut self) -> i32 {
+        let bytes = self.code[self.pc..self.pc + 4]
+            .try_into()
+            .expect("no enough bytes");
+        self.pc += 4;
+        i32::from_le_bytes(bytes)
+    }
+
+    #[inline(always)]
+    fn read_i64(&mut self) -> i64 {
+        let bytes = self.code[self.pc..self.pc + 8]
+            .try_into()
+            .expect("no enough bytes");
+        self.pc += 8;
+        i64::from_le_bytes(bytes)
+    }
+
+    #[inline(always)]
+    fn read_f64(&mut self) -> f64 {
+        let bytes = self.code[self.pc..self.pc + 8]
+            .try_into()
+            .expect("no enough bytes");
+        self.pc += 8;
+        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)
+    }
+
+    pub fn disassemble_colored(&mut self) -> String {
+        self.disassemble_impl(true)
+    }
+
+    fn disassemble_impl(&mut self, color: bool) -> String {
+        let mut out = String::new();
+        if color {
+            let _ = writeln!(out, "{}", "=== Bytecode Disassembly ===".bold().white());
+            let _ = writeln!(
+                out,
+                "{} {}",
+                "Length:".white(),
+                format!("{} bytes", self.code.len()).cyan()
+            );
+        } else {
+            let _ = writeln!(out, "=== Bytecode Disassembly ===");
+            let _ = writeln!(out, "Length: {} bytes", self.code.len());
+        }
+
+        while self.pc < self.code.len() {
+            let start_pos = self.pc;
+            let op_byte = self.read_u8();
+            let (mnemonic, args) = self.decode_instruction(op_byte, start_pos);
+
+            let bytes_slice = &self.code[start_pos + 1..self.pc];
+            let mut chunks = bytes_slice.chunks(4);
+
+            let first_chunk = chunks.next().unwrap_or(&[]);
+            let bytes_str = {
+                let mut temp = format!("{:02x}", self.code[start_pos]);
+                for b in first_chunk {
+                    let _ = write!(&mut temp, " {:02x}", b);
+                }
+                temp
+            };
+
+            if color {
+                let sep = if args.is_empty() { "" } else { " " };
+                let _ = writeln!(
+                    out,
+                    "{}  {:<14} | {}{}{}",
+                    format!("{:04x}", start_pos).dimmed(),
+                    bytes_str.green(),
+                    mnemonic.yellow().bold(),
+                    sep,
+                    args.cyan()
+                );
+            } else {
+                let op_str = if args.is_empty() {
+                    mnemonic.to_string()
+                } else {
+                    format!("{} {}", mnemonic, args)
+                };
+                let _ = writeln!(out, "{:04x}  {:<14} | {}", start_pos, bytes_str, op_str);
+            }
+
+            for chunk in chunks {
+                let bytes_str = {
+                    let mut temp = String::from("  ");
+                    for b in chunk {
+                        let _ = write!(&mut temp, " {:02x}", b);
+                    }
+                    temp
+                };
+
+                let extra_width = if start_pos > 0 {
+                    start_pos.ilog2() >> 4
+                } else {
+                    0
+                };
+
+                if color {
+                    let _ = write!(out, "    ");
+                    for _ in 0..extra_width {
+                        let _ = write!(out, " ");
+                    }
+                    let _ = writeln!(out, "  {:<14} |", bytes_str.green());
+                } else {
+                    let _ = write!(out, "    ");
+                    for _ in 0..extra_width {
+                        let _ = write!(out, " ");
+                    }
+                    let _ = writeln!(out, "  {:<14} |", bytes_str);
+                }
+            }
+        }
+        out
+    }
+
+    fn decode_instruction(&mut self, op_byte: u8, current_pc: usize) -> (&'static str, String) {
+        let op = Op::try_from_primitive(op_byte).expect("invalid op code");
+
+        match op {
+            Op::PushSmi => {
+                let val = self.read_i32();
+                ("PushSmi", format!("{}", val))
+            }
+            Op::PushBigInt => {
+                let val = self.read_i64();
+                ("PushBigInt", format!("{}", val))
+            }
+            Op::PushFloat => {
+                let val = self.read_f64();
+                ("PushFloat", format!("{}", val))
+            }
+            Op::PushString => {
+                let idx = self.read_u32();
+                let s = self.ctx.resolve_string(idx);
+                let len = s.len();
+                let mut s_fmt = format!("{:?}", s);
+                if s_fmt.len() > 60 {
+                    s_fmt.truncate(57);
+                    #[allow(clippy::unwrap_used)]
+                    write!(s_fmt, "...\" (total {len} bytes)").unwrap();
+                }
+                ("PushString", format!("@{} {}", idx, s_fmt))
+            }
+            Op::PushNull => ("PushNull", String::new()),
+            Op::PushTrue => ("PushTrue", String::new()),
+            Op::PushFalse => ("PushFalse", String::new()),
+
+            Op::LoadLocal => {
+                let idx = self.read_u32();
+                ("LoadLocal", format!("[{}]", idx))
+            }
+            Op::LoadOuter => {
+                let depth = self.read_u8();
+                let idx = self.read_u32();
+                ("LoadOuter", format!("depth={} [{}]", depth, idx))
+            }
+            Op::StoreLocal => {
+                let idx = self.read_u32();
+                ("StoreLocal", format!("[{}]", idx))
+            }
+            Op::AllocLocals => {
+                let count = self.read_u32();
+                ("AllocLocals", format!("count={}", count))
+            }
+
+            Op::MakeThunk => {
+                let offset = self.read_u32();
+                ("MakeThunk", format!("-> {:04x}", offset))
+            }
+            Op::MakeClosure => {
+                let offset = self.read_u32();
+                let slots = self.read_u32();
+                ("MakeClosure", format!("-> {:04x} slots={}", offset, slots))
+            }
+            Op::MakePatternClosure => {
+                let offset = self.read_u32();
+                let slots = self.read_u32();
+                let req_count = self.read_u16();
+                let opt_count = self.read_u16();
+                let ellipsis = self.read_u8() != 0;
+
+                let mut arg_str = format!(
+                    "-> {:04x} slots={} req={} opt={} ...={})",
+                    offset, slots, req_count, opt_count, ellipsis
+                );
+
+                arg_str.push_str(" Args=[");
+                for _ in 0..req_count {
+                    let idx = self.read_u32();
+                    arg_str.push_str(&format!("Req({}) ", self.ctx.resolve_string(idx)));
+                }
+                for _ in 0..opt_count {
+                    let idx = self.read_u32();
+                    arg_str.push_str(&format!("Opt({}) ", self.ctx.resolve_string(idx)));
+                }
+
+                let total_args = req_count + opt_count;
+                for _ in 0..total_args {
+                    let _name_idx = self.read_u32();
+                    let _span_id = self.read_u32();
+                }
+                arg_str.push(']');
+
+                ("MakePatternClosure", arg_str)
+            }
+
+            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 static_count = self.read_u32();
+                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::SelectStatic => {
+                let span_id = self.read_u32();
+                let key_id = self.read_u32();
+                (
+                    "SelectStatic",
+                    format!("key={} span={}", self.ctx.resolve_string(key_id), span_id),
+                )
+            }
+            Op::SelectDynamic => {
+                let span_id = self.read_u32();
+                ("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()),
+
+            Op::OpAdd => ("OpAdd", String::new()),
+            Op::OpSub => ("OpSub", String::new()),
+            Op::OpMul => ("OpMul", String::new()),
+            Op::OpDiv => ("OpDiv", String::new()),
+            Op::OpEq => ("OpEq", String::new()),
+            Op::OpNeq => ("OpNeq", String::new()),
+            Op::OpLt => ("OpLt", String::new()),
+            Op::OpGt => ("OpGt", String::new()),
+            Op::OpLeq => ("OpLeq", String::new()),
+            Op::OpGeq => ("OpGeq", String::new()),
+            Op::OpConcat => ("OpConcat", String::new()),
+            Op::OpUpdate => ("OpUpdate", String::new()),
+            Op::OpNeg => ("OpNeg", String::new()),
+            Op::OpNot => ("OpNot", String::new()),
+
+            Op::JumpIfFalse => {
+                let offset = self.read_i32();
+                let target = (current_pc as isize + 1 + 4 + offset as isize) as usize;
+                (
+                    "JumpIfFalse",
+                    format!("-> {:04x} offset={}", target, offset),
+                )
+            }
+            Op::JumpIfTrue => {
+                let offset = self.read_i32();
+                let target = (current_pc as isize + 1 + 4 + offset as isize) as usize;
+                ("JumpIfTrue", format!("-> {:04x} offset={}", target, offset))
+            }
+            Op::Jump => {
+                let offset = self.read_i32();
+                let target = (current_pc as isize + 1 + 4 + offset as isize) as usize;
+                ("Jump", format!("-> {:04x} offset={}", target, offset))
+            }
+
+            Op::ConcatStrings => {
+                let count = self.read_u16();
+                let force = self.read_u8();
+                ("ConcatStrings", format!("count={} force={}", count, force))
+            }
+            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::LookupWith => {
+                let idx = self.read_u32();
+                let name = self.ctx.resolve_string(idx);
+                let n = self.read_u8();
+                for _ in 0..n {
+                    self.read_operand_data();
+                }
+                ("LookupWith", format!("sym={:?} n={}", name, n))
+            }
+
+            Op::LoadBuiltins => ("LoadBuiltins", String::new()),
+            Op::LoadBuiltin => {
+                let id = self.read_u8();
+                ("LoadBuiltin", format!("id={}", 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!("slot={} {:?}", slot, name))
+            }
+            Op::Return => ("Return", String::new()),
+            Op::Illegal => ("Illegal", String::new()),
+        }
+    }
+}

fix-codegen/src/lib.rs

@@ -0,0 +1,903 @@
+use fix_builtins::{BUILTINS, BuiltinId};
+use fix_common::StringId;
+use fix_ir::{Attr, BinOpKind, Ir, MaybeThunk, Param, RawIrRef, ThunkId, UnOpKind};
+use hashbrown::HashMap;
+use num_enum::TryFromPrimitive;
+use rnix::TextRange;
+use string_interner::Symbol as _;
+
+pub mod disassembler;
+
+pub struct InstructionPtr(pub usize);
+
+pub trait BytecodeContext {
+    fn intern_string(&mut self, s: &str) -> StringId;
+    fn register_span(&mut self, range: TextRange) -> u32;
+    fn get_code(&self) -> &[u8];
+    fn get_code_mut(&mut self) -> &mut Vec<u8>;
+    fn add_constant(&mut self, val: Const) -> u32;
+    fn current_source_dir(&mut self) -> StringId;
+    fn current_scope_slot(&self) -> Option<u32>;
+}
+
+#[repr(u8)]
+#[derive(Debug, Clone, Copy, TryFromPrimitive)]
+#[allow(clippy::enum_variant_names)]
+pub enum Op {
+    PushSmi,
+    PushBigInt,
+    PushFloat,
+    PushString,
+    PushNull,
+    PushTrue,
+    PushFalse,
+
+    LoadLocal,
+    LoadOuter,
+    StoreLocal,
+    AllocLocals,
+
+    MakeThunk,
+    MakeClosure,
+    MakePatternClosure,
+
+    Call,
+    DispatchPrimOp,
+
+    MakeAttrs,
+    MakeEmptyAttrs,
+    SelectStatic,
+    SelectDynamic,
+    HasAttrPathStatic,
+    HasAttrPathDynamic,
+    HasAttrStatic,
+    HasAttrDynamic,
+    HasAttrResolve,
+    JumpIfSelectSucceeded,
+    JumpIfSelectFailed,
+
+    MakeList,
+    MakeEmptyList,
+
+    OpAdd,
+    OpSub,
+    OpMul,
+    OpDiv,
+    OpEq,
+    OpNeq,
+    OpLt,
+    OpGt,
+    OpLeq,
+    OpGeq,
+    OpConcat,
+    OpUpdate,
+
+    OpNeg,
+    OpNot,
+
+    JumpIfFalse,
+    JumpIfTrue,
+    Jump,
+
+    CoerceToString,
+
+    ConcatStrings,
+    ResolvePath,
+
+    Assert,
+
+    LookupWith,
+
+    LoadBuiltins,
+    LoadBuiltin,
+
+    LoadReplBinding,
+    LoadScopedBinding,
+
+    Return,
+
+    Illegal,
+}
+
+struct ScopeInfo {
+    depth: u8,
+    thunk_map: HashMap<ThunkId, u32>,
+}
+
+struct BytecodeEmitter<'a, Ctx: BytecodeContext> {
+    ctx: &'a mut Ctx,
+    scope_stack: Vec<ScopeInfo>,
+}
+
+#[repr(u8)]
+#[derive(Debug, Clone, Copy, TryFromPrimitive)]
+pub enum OperandType {
+    Const,
+    BigInt,
+    Local,
+    BuiltinConst,
+    Builtins,
+    ReplBinding,
+    ScopedImportBinding,
+}
+
+pub enum Const {
+    Smi(i32),
+    Float(f64),
+    Bool(bool),
+    String(StringId),
+    Path(StringId),
+    PrimOp {
+        id: BuiltinId,
+        arity: u8,
+        dispatch_ip: u32,
+    },
+    Null,
+}
+
+#[repr(u8)]
+#[derive(Debug, Clone, Copy, TryFromPrimitive)]
+pub enum AttrKeyType {
+    Static,
+    Dynamic,
+}
+
+pub enum InlineOperand {
+    Const(Const),
+    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 {
+    let ip = ctx.get_code().len();
+    let mut emitter = BytecodeEmitter::new(ctx);
+    emitter.emit_toplevel(ir);
+    InstructionPtr(ip)
+}
+
+impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
+    fn new(ctx: &'a mut Ctx) -> Self {
+        Self {
+            ctx,
+            scope_stack: Vec::with_capacity(32),
+        }
+    }
+
+    #[must_use]
+    fn inline_maybe_thunk(&self, val: &MaybeThunk) -> InlineOperand {
+        use MaybeThunk::*;
+        match *val {
+            Int(x) => {
+                if let Ok(x) = x.try_into() {
+                    InlineOperand::Const(Const::Smi(x))
+                } else {
+                    InlineOperand::BigInt(x)
+                }
+            }
+            Float(x) => InlineOperand::Const(Const::Float(x)),
+            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 { layer, local: 0 },
+            Builtin(id) => {
+                let (_, arity) = BUILTINS[id as usize];
+                InlineOperand::Const(Const::PrimOp {
+                    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) {
+        use InlineOperand::*;
+        let operand = self.inline_maybe_thunk(val);
+        match operand {
+            Const(val) => {
+                let idx = self.ctx.add_constant(val);
+                self.emit_u8(OperandType::Const as u8);
+                self.emit_u32(idx);
+            }
+            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);
+            }
+        }
+    }
+
+    #[inline]
+    fn emit_op(&mut self, op: Op) {
+        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);
+    }
+
+    #[inline]
+    fn emit_u16(&mut self, val: u16) {
+        self.ctx
+            .get_code_mut()
+            .extend_from_slice(&val.to_le_bytes());
+    }
+
+    #[inline]
+    fn emit_u32(&mut self, val: u32) {
+        self.ctx
+            .get_code_mut()
+            .extend_from_slice(&val.to_le_bytes());
+    }
+
+    #[inline]
+    fn emit_i32(&mut self, val: i32) {
+        self.ctx
+            .get_code_mut()
+            .extend_from_slice(&val.to_le_bytes());
+    }
+
+    #[inline]
+    fn emit_i64(&mut self, val: i64) {
+        self.ctx
+            .get_code_mut()
+            .extend_from_slice(&val.to_le_bytes());
+    }
+
+    #[inline]
+    fn emit_f64(&mut self, val: f64) {
+        self.ctx
+            .get_code_mut()
+            .extend_from_slice(&val.to_le_bytes());
+    }
+
+    #[inline]
+    fn emit_i32_placeholder(&mut self) -> usize {
+        let offset = self.ctx.get_code_mut().len();
+        self.ctx.get_code_mut().extend_from_slice(&[0u8; 4]);
+        offset
+    }
+    #[inline]
+    fn patch_i32(&mut self, offset: usize, val: i32) {
+        self.ctx.get_code_mut()[offset..offset + 4].copy_from_slice(&val.to_le_bytes());
+    }
+
+    #[inline]
+    fn emit_jump_placeholder(&mut self) -> usize {
+        self.emit_op(Op::Jump);
+        self.emit_i32_placeholder()
+    }
+
+    #[inline]
+    fn patch_jump_target(&mut self, placeholder_offset: usize) {
+        let current_pos = self.ctx.get_code_mut().len();
+        let relative_offset = (current_pos as i32) - (placeholder_offset as i32) - 4;
+        self.patch_i32(placeholder_offset, relative_offset);
+    }
+
+    #[inline]
+    fn emit_str_id(&mut self, id: StringId) {
+        self.ctx
+            .get_code_mut()
+            .extend_from_slice(&(id.0.to_usize() as u32).to_le_bytes());
+    }
+
+    fn current_depth(&self) -> u8 {
+        self.scope_stack.last().map_or(0, |s| s.depth)
+    }
+
+    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;
+                return (layer, local_idx);
+            }
+        }
+        panic!("ThunkId {:?} not found in any scope", id);
+    }
+
+    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);
+            self.emit_u32(local);
+        }
+    }
+
+    fn push_scope(&mut self, has_arg: bool, thunk_ids: &[ThunkId]) {
+        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()
+            .enumerate()
+            .map(|(i, &id)| (id, thunk_base + i as u32))
+            .collect();
+        self.scope_stack.push(ScopeInfo { depth, thunk_map });
+    }
+
+    fn pop_scope(&mut self) {
+        self.scope_stack.pop();
+    }
+
+    fn emit_toplevel(&mut self, ir: RawIrRef<'_>) {
+        match ir {
+            &Ir::TopLevel { body, ref thunks } => {
+                let thunk_ids: Vec<ThunkId> = thunks.iter().map(|&(id, _)| id).collect();
+                self.push_scope(false, &thunk_ids);
+                if !thunks.is_empty() {
+                    self.emit_op(Op::AllocLocals);
+                    self.emit_u32(thunks.len().try_into().expect("too many thunks"));
+                }
+
+                self.emit_scope_thunks(thunks);
+                self.emit_expr(body);
+                self.emit_op(Op::Return);
+
+                self.pop_scope();
+            }
+            _ => {
+                self.push_scope(false, &[]);
+                self.emit_expr(ir);
+                self.emit_op(Op::Return);
+                self.pop_scope();
+            }
+        }
+    }
+
+    fn emit_scope_thunks(&mut self, thunks: &[(ThunkId, RawIrRef<'_>)]) {
+        for &(id, inner) in thunks {
+            let skip_patch = self.emit_jump_placeholder();
+            let entry_point = self.ctx.get_code_mut().len() as u32;
+            self.emit_expr(inner);
+            self.emit_op(Op::Return);
+            self.patch_jump_target(skip_patch);
+            self.emit_op(Op::MakeThunk);
+            self.emit_u32(entry_point);
+            let (_, local_idx) = self.resolve_thunk(id);
+            self.emit_op(Op::StoreLocal);
+            self.emit_u32(local_idx);
+        }
+    }
+
+    fn emit_expr(&mut self, ir: RawIrRef<'_>) {
+        match ir {
+            &Ir::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);
+                }
+            }
+            &Ir::Float(x) => {
+                self.emit_op(Op::PushFloat);
+                self.emit_f64(x);
+            }
+            &Ir::Bool(true) => self.emit_op(Op::PushTrue),
+            &Ir::Bool(false) => self.emit_op(Op::PushFalse),
+            Ir::Null => self.emit_op(Op::PushNull),
+            &Ir::Str(id) => {
+                self.emit_op(Op::PushString);
+                self.emit_str_id(id);
+            }
+            &Ir::Path(p) => {
+                self.emit_expr(p);
+                self.emit_op(Op::ResolvePath);
+                let dir_id = self.ctx.current_source_dir();
+                self.emit_str_id(dir_id);
+            }
+            &Ir::If { cond, consq, alter } => {
+                self.emit_expr(cond);
+
+                self.emit_op(Op::JumpIfFalse);
+                let else_placeholder = self.emit_i32_placeholder();
+                let after_jif = self.ctx.get_code_mut().len();
+
+                self.emit_expr(consq);
+
+                self.emit_op(Op::Jump);
+                let end_placeholder = self.emit_i32_placeholder();
+                let after_jump = self.ctx.get_code_mut().len();
+
+                let else_offset = (after_jump as i32) - (after_jif as i32);
+                self.patch_i32(else_placeholder, else_offset);
+
+                self.emit_expr(alter);
+
+                let end_offset = (self.ctx.get_code_mut().len() as i32) - (after_jump as i32);
+                self.patch_i32(end_placeholder, end_offset);
+            }
+            &Ir::BinOp { lhs, rhs, kind } => {
+                self.emit_binop(lhs, rhs, kind);
+            }
+            &Ir::UnOp { rhs, kind } => match kind {
+                UnOpKind::Neg => {
+                    self.emit_expr(rhs);
+                    self.emit_op(Op::OpNeg);
+                }
+                UnOpKind::Not => {
+                    self.emit_expr(rhs);
+                    self.emit_op(Op::OpNot);
+                }
+            },
+            &Ir::Func {
+                body,
+                ref param,
+                ref thunks,
+            } => {
+                self.emit_func(thunks, param, body);
+            }
+            Ir::AttrSet { stcs, dyns } => {
+                self.emit_attrset(stcs, dyns);
+            }
+            Ir::List { items } => {
+                if items.is_empty() {
+                    self.emit_op(Op::MakeEmptyList);
+                } else {
+                    self.emit_op(Op::MakeList);
+                    self.emit_u32(items.len() as u32);
+                    for &item in items.iter() {
+                        self.emit_maybe_thunk(item);
+                    }
+                }
+            }
+            &Ir::Call { func, arg, .. } => {
+                self.emit_expr(func);
+                self.emit_op(Op::Call);
+                self.emit_maybe_thunk(arg);
+            }
+            &Ir::Arg { layer } => {
+                self.emit_load(layer, 0);
+            }
+            &Ir::TopLevel { body, ref thunks } => {
+                self.emit_toplevel_inner(body, thunks);
+            }
+            &Ir::Select {
+                expr,
+                ref attrpath,
+                default,
+                span,
+            } => {
+                self.emit_select(expr, attrpath, default, span);
+            }
+            Ir::Builtins => {
+                self.emit_op(Op::LoadBuiltins);
+            }
+            &Ir::Builtin(id) => {
+                self.emit_op(Op::LoadBuiltin);
+                self.emit_u8(id as u8);
+            }
+            &Ir::BuiltinConst(id) => {
+                self.emit_select(
+                    &Ir::Builtins,
+                    &[Attr::Str(id, TextRange::default())],
+                    None,
+                    TextRange::default(),
+                );
+            }
+            &Ir::ConcatStrings {
+                ref parts,
+                force_string,
+            } => {
+                for &part in parts.iter() {
+                    self.emit_expr(part);
+                    self.emit_op(Op::CoerceToString);
+                }
+                self.emit_op(Op::ConcatStrings);
+                self.emit_u16(parts.len() as u16);
+                self.emit_bool(force_string);
+            }
+            &Ir::HasAttr { lhs, ref rhs } => {
+                self.emit_has_attr(lhs, rhs);
+            }
+            Ir::Assert {
+                assertion,
+                expr,
+                assertion_raw,
+                span,
+            } => {
+                let raw_idx = self.ctx.intern_string(assertion_raw);
+                let span_id = self.ctx.register_span(*span);
+                self.emit_expr(*assertion);
+                self.emit_op(Op::Assert);
+                self.emit_str_id(raw_idx);
+                self.emit_u32(span_id);
+                self.emit_expr(*expr);
+            }
+            &Ir::ReplBinding(name) => {
+                self.emit_op(Op::LoadReplBinding);
+                self.emit_str_id(name);
+            }
+            &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::WithLookup { sym, namespaces } => {
+                // counter
+                self.emit_expr(&Ir::Int(0));
+                self.emit_op(Op::LookupWith);
+                self.emit_str_id(*sym);
+                self.emit_u8(
+                    namespaces
+                        .len()
+                        .try_into()
+                        .expect("too many `with` namespaces"),
+                );
+                for namespace in namespaces {
+                    self.emit_maybe_thunk(namespace);
+                }
+            }
+            &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);
+                    }
+                }
+            }
+        }
+    }
+
+    fn emit_binop(&mut self, lhs: RawIrRef<'_>, rhs: RawIrRef<'_>, kind: BinOpKind) {
+        use BinOpKind::*;
+        match kind {
+            And => {
+                self.emit_expr(lhs);
+                self.emit_op(Op::JumpIfFalse);
+                let skip_placeholder = self.emit_i32_placeholder();
+                let after_jif = self.ctx.get_code_mut().len();
+
+                self.emit_expr(rhs);
+                self.emit_op(Op::Jump);
+                let end_placeholder = self.emit_i32_placeholder();
+                let after_jump = self.ctx.get_code_mut().len();
+
+                let false_offset = (after_jump as i32) - (after_jif as i32);
+                self.patch_i32(skip_placeholder, false_offset);
+
+                self.emit_op(Op::PushFalse);
+
+                let end_offset = (self.ctx.get_code_mut().len() as i32) - (after_jump as i32);
+                self.patch_i32(end_placeholder, end_offset);
+            }
+            Or => {
+                self.emit_expr(lhs);
+                self.emit_op(Op::JumpIfTrue);
+                let skip_placeholder = self.emit_i32_placeholder();
+                let after_jit = self.ctx.get_code_mut().len();
+
+                self.emit_expr(rhs);
+                self.emit_op(Op::Jump);
+                let end_placeholder = self.emit_i32_placeholder();
+                let after_jump = self.ctx.get_code_mut().len();
+
+                let true_offset = (after_jump as i32) - (after_jit as i32);
+                self.patch_i32(skip_placeholder, true_offset);
+
+                self.emit_op(Op::PushTrue);
+
+                let end_offset = (self.ctx.get_code_mut().len() as i32) - (after_jump as i32);
+                self.patch_i32(end_placeholder, end_offset);
+            }
+            Impl => {
+                self.emit_expr(lhs);
+                self.emit_op(Op::JumpIfFalse);
+                let skip_placeholder = self.emit_i32_placeholder();
+                let after_jif = self.ctx.get_code_mut().len();
+
+                self.emit_expr(rhs);
+                self.emit_op(Op::Jump);
+                let end_placeholder = self.emit_i32_placeholder();
+                let after_jump = self.ctx.get_code_mut().len();
+
+                let true_offset = (after_jump as i32) - (after_jif as i32);
+                self.patch_i32(skip_placeholder, true_offset);
+
+                self.emit_op(Op::PushTrue);
+
+                let end_offset = (self.ctx.get_code_mut().len() as i32) - (after_jump as i32);
+                self.patch_i32(end_placeholder, end_offset);
+            }
+            _ => {
+                self.emit_expr(lhs);
+                self.emit_expr(rhs);
+                self.emit_op(match kind {
+                    Add => Op::OpAdd,
+                    Sub => Op::OpSub,
+                    Mul => Op::OpMul,
+                    Div => Op::OpDiv,
+                    Eq => Op::OpEq,
+                    Neq => Op::OpNeq,
+                    Lt => Op::OpLt,
+                    Gt => Op::OpGt,
+                    Leq => Op::OpLeq,
+                    Geq => Op::OpGeq,
+                    Con => Op::OpConcat,
+                    Upd => Op::OpUpdate,
+                    _ => unreachable!(),
+                });
+            }
+        }
+    }
+
+    fn emit_func<'ir>(
+        &mut self,
+        thunks: &[(ThunkId, RawIrRef<'ir>)],
+        param: &Option<Param<'ir>>,
+        body: RawIrRef<'ir>,
+    ) {
+        let thunk_ids: Vec<ThunkId> = thunks.iter().map(|&(id, _)| id).collect();
+
+        let skip_patch = self.emit_jump_placeholder();
+        let entry_point = self.ctx.get_code().len() as u32;
+        self.push_scope(true, &thunk_ids);
+        self.emit_scope_thunks(thunks);
+        self.emit_expr(body);
+        self.emit_op(Op::Return);
+        self.pop_scope();
+        self.patch_jump_target(skip_patch);
+
+        if let Some(Param {
+            required,
+            optional,
+            ellipsis,
+        }) = param
+        {
+            self.emit_op(Op::MakePatternClosure);
+            self.emit_u32(entry_point);
+            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_bool(*ellipsis);
+
+            for &(sym, _) in required.iter() {
+                self.emit_str_id(sym);
+            }
+            for &(sym, _) in optional.iter() {
+                self.emit_str_id(sym);
+            }
+            for &(sym, span) in required.iter().chain(optional.iter()) {
+                let span_id = self.ctx.register_span(span);
+                self.emit_str_id(sym);
+                self.emit_u32(span_id);
+            }
+        } else {
+            self.emit_op(Op::MakeClosure);
+            self.emit_u32(entry_point);
+            self.emit_u32(thunks.len().try_into().expect("too many thunks"));
+        }
+    }
+
+    fn emit_attrset(
+        &mut self,
+        stcs: &fix_ir::HashMap<'_, StringId, (&MaybeThunk, TextRange)>,
+        dyns: &[(RawIrRef<'_>, &MaybeThunk, TextRange)],
+    ) {
+        if stcs.is_empty() && dyns.is_empty() {
+            self.emit_op(Op::MakeEmptyAttrs);
+            return;
+        }
+
+        for &(key_expr, _val, _span) in dyns.iter() {
+            self.emit_expr(key_expr);
+        }
+
+        self.emit_op(Op::MakeAttrs);
+        self.emit_u32(stcs.len() as u32);
+        self.emit_u32(dyns.len() as u32);
+
+        for (&sym, &(val, span)) in stcs.iter() {
+            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() {
+            self.emit_maybe_thunk(val);
+            let span_id = self.ctx.register_span(span);
+            self.emit_u32(span_id);
+        }
+    }
+
+    fn emit_select(
+        &mut self,
+        expr: RawIrRef<'_>,
+        attrpath: &[Attr<RawIrRef<'_>>],
+        default: Option<RawIrRef<'_>>,
+        span: TextRange,
+    ) {
+        self.emit_expr(expr);
+
+        let mut dynamic_patches = Vec::new();
+        for attr in attrpath.iter() {
+            match *attr {
+                Attr::Str(sym, _) => {
+                    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(key_expr, _) => {
+                    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);
+
+        let mut dynamic_patches = Vec::new();
+        let [attrs @ .., last] = rhs else {
+            panic!("attrpath is empty");
+        };
+        for attr in attrs {
+            match *attr {
+                Attr::Str(sym, span) => {
+                    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(key_expr, span) => {
+                    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, _) => {
+                self.emit_op(Op::JumpIfSelectFailed);
+                dynamic_patches.push(self.emit_i32_placeholder());
+                self.emit_expr(key_expr);
+                self.emit_op(Op::HasAttrDynamic);
+            }
+        }
+        for patch in dynamic_patches {
+            self.patch_jump_target(patch);
+        }
+        self.emit_op(Op::HasAttrResolve);
+    }
+
+    fn emit_toplevel_inner(&mut self, body: RawIrRef<'_>, thunks: &[(ThunkId, RawIrRef<'_>)]) {
+        self.emit_scope_thunks(thunks);
+        self.emit_expr(body);
+    }
+}

fix-common/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "fix-common"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+gc-arena = { workspace = true }
+string-interner = { workspace = true }
+ere = { workspace = true }

fix-common/src/lib.rs

@@ -1,14 +1,17 @@
-use core::fmt::{Debug, Display, Formatter, Result as FmtResult};
-use core::hash::Hash;
-use core::ops::Deref;
 use std::borrow::Cow;
 use std::collections::BTreeMap;
-use std::ops::DerefMut;
+use std::fmt::{Debug, Display, Formatter, Result as FmtResult};
+use std::ops::{Deref, DerefMut};
 
-use derive_more::{Constructor, IsVariant, Unwrap};
+use gc_arena::Collect;
+
+#[repr(transparent)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Collect)]
+#[collect(require_static)]
+pub struct StringId(pub string_interner::symbol::SymbolU32);
 
 /// Represents a Nix symbol, which is used as a key in attribute sets.
-#[derive(Debug, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Constructor)]
+#[derive(Debug, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Symbol<'a>(Cow<'a, str>);
 
 pub type StaticSymbol = Symbol<'static>;
@@ -60,13 +63,36 @@ impl Deref for Symbol<'_> {
     }
 }
 
+fn escape_quote_string(s: &str) -> String {
+    let mut ret = String::with_capacity(s.len() + 2);
+    ret.push('"');
+    let mut iter = s.chars().peekable();
+    while let Some(c) = iter.next() {
+        match c {
+            '\\' => ret.push_str("\\\\"),
+            '"' => ret.push_str("\\\""),
+            '\n' => ret.push_str("\\n"),
+            '\r' => ret.push_str("\\r"),
+            '\t' => ret.push_str("\\t"),
+            '$' if iter.peek() == Some(&'{') => ret.push_str("\\$"),
+            c => ret.push(c),
+        }
+    }
+    ret.push('"');
+    ret
+}
+
 /// Represents a Nix attribute set, which is a map from symbols to values.
-#[derive(Constructor, Default, Clone, PartialEq)]
+#[derive(Default, Clone, PartialEq)]
 pub struct AttrSet {
     data: BTreeMap<StaticSymbol, Value>,
 }
 
 impl AttrSet {
+    pub fn new(data: BTreeMap<StaticSymbol, Value>) -> Self {
+        Self { data }
+    }
+
     /// Gets a value by key (string or Symbol).
     pub fn get<'a, 'sym: 'a>(&'a self, key: impl Into<Symbol<'sym>>) -> Option<&'a Value> {
         self.data.get(&key.into())
@@ -154,11 +180,17 @@ impl Display for AttrSetCompatDisplay<'_> {
 }
 
 /// Represents a Nix list, which is a vector of values.
-#[derive(Constructor, Default, Clone, Debug, PartialEq)]
+#[derive(Default, Clone, Debug, PartialEq)]
 pub struct List {
     data: Vec<Value>,
 }
 
+impl List {
+    pub fn new(data: Vec<Value>) -> Self {
+        Self { data }
+    }
+}
+
 impl Deref for List {
     type Target = Vec<Value>;
     fn deref(&self) -> &Self::Target {
@@ -217,7 +249,7 @@ impl Display for ListCompatDisplay<'_> {
 }
 
 /// Represents any possible Nix value that can be returned from an evaluation.
-#[derive(IsVariant, Unwrap, Clone, Debug, PartialEq)]
+#[derive(Clone, Debug, PartialEq)]
 pub enum Value {
     /// An integer value.
     Int(i64),
@@ -240,31 +272,21 @@ pub enum Value {
     /// A function (lambda).
     Func,
     /// A primitive (built-in) operation.
-    PrimOp(String),
+    PrimOp(&'static str),
     /// A partially applied primitive operation.
-    PrimOpApp(String),
+    PrimOpApp(&'static str),
     /// A marker for a value that has been seen before during serialization, to break cycles.
     /// This is used to prevent infinite recursion when printing or serializing cyclic data structures.
     Repeated,
 }
 
-fn escape_quote_string(s: &str) -> String {
+/// Wrapper to format a float in Nix style (C printf `%g` with precision 6).
-    let mut ret = String::with_capacity(s.len() + 2);
+pub struct NixFloat(pub f64);
-    ret.push('"');
+
-    let mut iter = s.chars().peekable();
+impl Display for NixFloat {
-    while let Some(c) = iter.next() {
+    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
-        match c {
+        fmt_nix_float(f, self.0)
-            '\\' => ret.push_str("\\\\"),
-            '"' => ret.push_str("\\\""),
-            '\n' => ret.push_str("\\n"),
-            '\r' => ret.push_str("\\r"),
-            '\t' => ret.push_str("\\t"),
-            '$' if iter.peek() == Some(&'{') => ret.push_str("\\$"),
-            c => ret.push(c),
     }
-    }
-    ret.push('"');
-    ret
 }
 
 /// Format a float matching C's `printf("%g", x)` with default precision 6.

fix-error/Cargo.toml

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

fix-error/src/lib.rs

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

fix-ir/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "fix-ir"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+bumpalo = { workspace = true }
+ghost-cell = { workspace = true }
+rnix = { workspace = true }
+rowan = { workspace = true }
+string-interner = { workspace = true }
+hashbrown = { workspace = true }
+num_enum = { workspace = true }
+
+fix-builtins = { path = "../fix-builtins" }
+fix-common = { path = "../fix-common" }
+fix-error = { path = "../fix-error" }

fix-ir/src/downgrade.rs

@@ -1,14 +1,14 @@
-use bumpalo::boxed::Box;
 use bumpalo::collections::{CollectIn, Vec};
+use fix_builtins::BuiltinId;
+use fix_common::Symbol;
+use fix_error::{Error, Result, Source};
 use hashbrown::HashSet;
 use hashbrown::hash_map::Entry;
 use rnix::TextRange;
-use rnix::ast::{self, Expr, HasEntry};
+use rnix::ast::{self, AstToken, Expr, HasEntry};
 use rowan::ast::AstNode;
 
-use crate::error::{Error, Result, Source};
+use super::*;
-use crate::ir::*;
-use crate::value::Symbol;
 
 trait Require<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, T> {
     fn require(self, ctx: &Ctx, span: TextRange) -> Result<T>;
@@ -38,34 +38,26 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, T, E: std::fmt::Display>
     }
 }
 
-trait BoxIn: Sized {
-    fn box_in(self, bump: &bumpalo::Bump) -> Box<'_, Self> {
-        Box::new_in(self, bump)
-    }
-}
-impl<T: Sized> BoxIn for T {}
-
 pub trait DowngradeContext<'id: 'ir, 'ir> {
-    fn new_expr(&self, expr: Ir<'ir, IrRef<'id, 'ir>>) -> IrRef<'id, 'ir>;
+    fn new_expr(&self, expr: Ir<'ir, GhostRoRef<'id, 'ir>>) -> GhostRoIrRef<'id, 'ir>;
-    fn new_arg(&mut self) -> ArgId;
+    fn maybe_thunk(&mut self, ir: GhostRoIrRef<'id, 'ir>) -> GhostRoMaybeThunkRef<'id, 'ir>;
-    fn maybe_thunk(&mut self, ir: IrRef<'id, 'ir>) -> IrRef<'id, 'ir>;
 
-    fn new_sym(&mut self, sym: String) -> SymId;
+    fn intern_string(&mut self, sym: impl AsRef<str>) -> StringId;
-    fn get_sym(&self, id: SymId) -> Symbol<'_>;
+    fn resolve_sym(&self, id: StringId) -> Symbol<'_>;
-    fn lookup(&self, sym: SymId, span: TextRange) -> Result<IrRef<'id, 'ir>>;
+    fn lookup(&mut self, sym: StringId, span: TextRange) -> Result<GhostRoMaybeThunkRef<'id, 'ir>>;
 
     fn get_current_source(&self) -> Source;
 
-    fn with_param_scope<F, R>(&mut self, param: SymId, arg: ArgId, f: F) -> R
+    fn with_param_scope<F, R>(&mut self, param: StringId, f: F) -> R
     where
         F: FnOnce(&mut Self) -> R;
-    fn with_let_scope<F, R>(&mut self, bindings: &[SymId], f: F) -> Result<R>
+    fn with_let_scope<F, R>(&mut self, bindings: &[StringId], f: F) -> Result<R>
     where
-        F: FnOnce(&mut Self) -> Result<(Vec<'ir, IrRef<'id, 'ir>>, R)>;
+        F: FnOnce(&mut Self) -> Result<(Vec<'ir, GhostRoMaybeThunkRef<'id, 'ir>>, R)>;
-    fn with_with_scope<F, R>(&mut self, f: F) -> R
+    fn with_with_scope<F, R>(&mut self, namespace: GhostRoMaybeThunkRef<'id, 'ir>, f: F) -> R
     where
         F: FnOnce(&mut Self) -> R;
-    fn with_thunk_scope<F, R>(&mut self, f: F) -> (R, Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>)
+    fn with_thunk_scope<F, R>(&mut self, f: F) -> (R, Vec<'ir, (ThunkId, GhostRoIrRef<'id, 'ir>)>)
     where
         F: FnOnce(&mut Self) -> R;
 
@@ -73,11 +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),
@@ -106,7 +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
@@ -122,7 +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();
@@ -138,7 +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)?;
@@ -150,9 +142,8 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 macro_rules! path {
     ($ty:ident) => {
         impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::$ty {
-            fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+            fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
-                let span = self.syntax().text_range();
+                downgrade_path(self.parts(), ctx)
-                downgrade_path(self.parts(), span, ctx)
             }
         }
     };
@@ -161,19 +152,20 @@ path!(PathAbs);
 path!(PathRel);
 path!(PathHome);
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::PathSearch {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let path = {
             let temp = self.content().require(ctx, span)?;
             let text = temp.text();
-            ctx.new_expr(Ir::Str(
+            let id = ctx.intern_string(&text[1..text.len() - 1]);
-                text[1..text.len() - 1].to_string().box_in(ctx.bump()),
+            let expr = ctx.new_expr(Ir::Str(id));
-            ))
+            ctx.maybe_thunk(expr)
         };
-        let sym = ctx.new_sym("findFile".into());
+        // HACK: disgusting eww
-        let find_file = ctx.new_expr(Ir::Builtin(sym));
+        let find_file = ctx.new_expr(Ir::Builtin(BuiltinId::FindFile));
-        let sym = ctx.new_sym("nixPath".into());
+        let sym = ctx.intern_string("nixPath");
-        let nix_path = ctx.new_expr(Ir::Builtin(sym));
+        let nix_path = ctx.new_expr(Ir::BuiltinConst(sym));
+        let nix_path = ctx.maybe_thunk(nix_path);
         let call = ctx.new_expr(Ir::Call {
             func: find_file,
             arg: nix_path,
@@ -188,29 +180,27 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Str {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let normalized = self.normalized_parts();
         let is_single_literal = normalized.len() == 1
             && matches!(normalized.first(), Some(ast::InterpolPart::Literal(_)));
 
         let bump = ctx.bump();
-        let parts = normalized
+        let mut parts = normalized.into_iter().map(|part| match part {
-            .into_iter()
+            ast::InterpolPart::Literal(lit) => {
-            .map(|part| match part {
+                let id = ctx.intern_string(lit);
-                ast::InterpolPart::Literal(lit) => Ok(ctx.new_expr(Ir::Str(lit.box_in(bump)))),
+                Ok(ctx.new_expr(Ir::Str(id)))
-                ast::InterpolPart::Interpolation(interpol) => {
+            }
-                    let inner = interpol
+            ast::InterpolPart::Interpolation(interpol) => interpol
                 .expr()
                 .require(ctx, interpol.syntax().text_range())?
-                        .downgrade(ctx)?;
+                .downgrade(ctx),
-                    Ok(ctx.maybe_thunk(inner))
+        });
-                }
-            })
-            .collect_in::<Result<Vec<'ir, _>>>(bump)?;
 
         Ok(if is_single_literal {
-            parts.into_iter().next().expect("is_single_literal checked")
+            parts.next().expect("is_single_literal checked")?
         } else {
+            let parts = parts.collect_in::<Result<_>>(bump)?;
             ctx.new_expr(Ir::ConcatStrings {
                 parts,
                 force_string: true,
@@ -220,27 +210,88 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Literal {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
-        Ok(ctx.new_expr(match self.kind() {
+        let expr = match self.kind() {
             ast::LiteralKind::Integer(int) => Ir::Int(int.value().require(ctx, span)?),
             ast::LiteralKind::Float(float) => Ir::Float(float.value().require(ctx, span)?),
-            ast::LiteralKind::Uri(uri) => Ir::Str(uri.to_string().box_in(ctx.bump())),
+            ast::LiteralKind::Uri(uri) => {
-        }))
+                let id = ctx.intern_string(uri.syntax().text());
+                Ir::Str(id)
+            }
+        };
+        Ok(ctx.new_expr(expr))
     }
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Ident {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let text = self.ident_token().require(ctx, span)?.to_string();
-        let sym = ctx.new_sym(text);
+        let sym = ctx.intern_string(text);
         ctx.lookup(sym, span)
+            .map(|thunk| ctx.new_expr(Ir::MaybeThunk(thunk)))
+    }
+}
+
+impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::CurPos {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
+        fn byte_offset_to_line_col(content: &str, offset: usize) -> (u32, u32) {
+            let mut line = 1u32;
+            let mut col = 1u32;
+
+            for (idx, ch) in content.char_indices() {
+                if idx >= offset {
+                    break;
+                }
+                if ch == '\n' {
+                    line += 1;
+                    col = 1;
+                } else {
+                    col += 1;
+                }
+            }
+
+            (line, col)
+        }
+
+        let span = self.syntax().text_range();
+        let source = ctx.get_current_source();
+        let (line, column) = byte_offset_to_line_col(&source.src, span.start().into());
+
+        let file_sym = ctx.intern_string("file");
+        let line_sym = ctx.intern_string("line");
+        let column_sym = ctx.intern_string("column");
+
+        let file: GhostRoMaybeThunkRef = ctx
+            .bump()
+            .alloc(GhostCell::new(MaybeThunk::Str(ctx.intern_string(source.get_name()))).into());
+        let line = ctx
+            .bump()
+            .alloc(GhostCell::new(MaybeThunk::Int(i64::from(line))).into());
+        let column = ctx
+            .bump()
+            .alloc(GhostCell::new(MaybeThunk::Int(i64::from(column))).into());
+
+        let map = {
+            let mut map = HashMap::new_in(ctx.bump());
+
+            map.insert(file_sym, (file, TextRange::default()));
+            map.insert(line_sym, (line, TextRange::default()));
+            map.insert(column_sym, (column, TextRange::default()));
+
+            map
+        };
+
+        Ok(ctx.new_expr(Ir::AttrSet {
+            stcs: map,
+            dyns: Vec::new_in(ctx.bump()),
+        }))
     }
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::AttrSet {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let rec = self.rec_token().is_some();
         if !rec {
             let attrs = downgrade_attrs(self, ctx)?;
@@ -256,7 +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()
@@ -270,17 +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)?;
@@ -289,7 +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();
@@ -298,16 +384,14 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Select {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let expr = self.expr().require(ctx, span)?.downgrade(ctx)?;
         let attrpath = downgrade_attrpath(self.attrpath().require(ctx, span)?, ctx)?;
-        let default = if let Some(default) = self.default_expr() {
+        let default = self
-            let default_expr = default.downgrade(ctx)?;
+            .default_expr()
-            Some(ctx.maybe_thunk(default_expr))
+            .map(|expr| expr.downgrade(ctx))
-        } else {
+            .transpose()?;
-            None
-        };
         let span = self.syntax().text_range();
         Ok(ctx.new_expr(Ir::Select {
             expr,
@@ -319,7 +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| {
@@ -334,7 +418,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
             Ok(ctx.new_expr(Ir::AttrSet { stcs, dyns }))
         })?;
 
-        let body_sym = ctx.new_sym("body".to_string());
+        let body_sym = ctx.intern_string("body");
         Ok(ctx.new_expr(Ir::Select {
             expr: attrset_expr,
             attrpath: Vec::from_iter_in(
@@ -348,7 +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)?;
@@ -358,34 +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)?;
-        let arg = ctx.new_arg();
 
         struct Ret<'id, 'ir> {
             param: Option<Param<'ir>>,
-            body: IrRef<'id, 'ir>,
+            body: GhostRoIrRef<'id, 'ir>,
         }
 
         let (ret, thunks) = ctx.with_thunk_scope(|ctx| {
@@ -394,18 +469,17 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 
             match raw_param {
                 ast::Param::IdentParam(id) => {
-                    let param_sym = ctx.new_sym(id.to_string());
+                    let param_sym = ctx.intern_string(id.to_string());
                     param = None;
 
-                    body = ctx
+                    body = ctx.with_param_scope(param_sym, |ctx| body_ast.downgrade(ctx))?;
-                        .with_param_scope(param_sym, arg, |ctx| body_ast.clone().downgrade(ctx))?;
                 }
                 ast::Param::Pattern(pattern) => {
                     let alias = pattern
                         .pat_bind()
                         .map(|alias| {
                             let ident = alias.ident().require(ctx, alias.syntax().text_range())?;
-                            Ok::<_, std::boxed::Box<Error>>(ctx.new_sym(ident.to_string()))
+                            Ok::<_, std::boxed::Box<Error>>(ctx.intern_string(ident.to_string()))
                         })
                         .transpose()?;
 
@@ -416,7 +490,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
                         body: inner_body,
                         required,
                         optional,
-                    } = downgrade_pattern_bindings(pat_entries, alias, arg, ctx, |ctx, _| {
+                    } = downgrade_pattern_bindings(pat_entries, alias, ctx, |ctx, _| {
                         body_ast.clone().downgrade(ctx)
                     })?;
 
@@ -437,14 +511,13 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
         Ok(ctx.new_expr(Ir::Func {
             body,
             param,
-            arg,
             thunks,
         }))
     }
 }
 
 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)?;
@@ -456,8 +529,8 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 
 enum PendingValue<'ir> {
     Expr(ast::Expr),
-    InheritFrom(ast::Expr, SymId, TextRange),
+    InheritFrom(ast::Expr, StringId, TextRange),
-    InheritScope(SymId, TextRange),
+    InheritScope(StringId, TextRange),
     Set(PendingAttrSet<'ir>),
     ExtendedRecAttrSet {
         base: ast::AttrSet,
@@ -466,7 +539,7 @@ enum PendingValue<'ir> {
 }
 
 struct PendingAttrSet<'ir> {
-    stcs: HashMap<'ir, SymId, (PendingValue<'ir>, TextRange)>,
+    stcs: HashMap<'ir, StringId, (PendingValue<'ir>, TextRange)>,
     dyns: Vec<'ir, (ast::Attr, PendingValue<'ir>, TextRange)>,
 }
 
@@ -490,7 +563,7 @@ impl<'id: 'ir, 'ir> PendingAttrSet<'ir> {
 
         match first {
             ast::Attr::Ident(ident) => {
-                let sym = ctx.new_sym(ident.to_string());
+                let sym = ctx.intern_string(ident.to_string());
                 self.insert_static(sym, span, rest, value, ctx)
             }
             ast::Attr::Str(string) => {
@@ -499,7 +572,7 @@ impl<'id: 'ir, 'ir> PendingAttrSet<'ir> {
                     && let ast::InterpolPart::Literal(lit) =
                         parts.into_iter().next().expect("len checked")
                 {
-                    let sym = ctx.new_sym(lit);
+                    let sym = ctx.intern_string(lit);
                     return self.insert_static(sym, span, rest, value, ctx);
                 }
                 self.insert_dynamic(first.clone(), span, rest, value, ctx)
@@ -510,7 +583,7 @@ impl<'id: 'ir, 'ir> PendingAttrSet<'ir> {
 
     fn insert_static(
         &mut self,
-        sym: SymId,
+        sym: StringId,
         span: TextRange,
         path: &[ast::Attr],
         value: ast::Expr,
@@ -742,14 +815,14 @@ impl<'id: 'ir, 'ir> PendingAttrSet<'ir> {
         for attr in inherit.attrs() {
             let span = attr.syntax().text_range();
             let sym = match &attr {
-                ast::Attr::Ident(ident) => ctx.new_sym(ident.to_string()),
+                ast::Attr::Ident(ident) => ctx.intern_string(ident.to_string()),
                 ast::Attr::Str(s) => {
                     let parts = s.normalized_parts();
                     if parts.len() == 1
                         && let ast::InterpolPart::Literal(lit) =
                             parts.into_iter().next().expect("len checked")
                     {
-                        ctx.new_sym(lit)
+                        ctx.intern_string(lit)
                     } else {
                         return Err(Error::downgrade_error(
                             "dynamic attributes not allowed in inherit".to_string(),
@@ -769,7 +842,7 @@ impl<'id: 'ir, 'ir> PendingAttrSet<'ir> {
 
             if self.stcs.contains_key(&sym) {
                 return Err(Error::downgrade_error(
-                    format!("attribute '{}' already defined", ctx.get_sym(sym)),
+                    format!("attribute '{}' already defined", ctx.resolve_sym(sym)),
                     ctx.get_current_source(),
                     span,
                 ));
@@ -846,8 +919,15 @@ fn make_attrpath_value_entry<'ir>(path: Vec<'ir, ast::Attr>, value: ast::Expr) -
 }
 
 struct FinalizedAttrSet<'id, 'ir> {
-    stcs: HashMap<'ir, SymId, (IrRef<'id, 'ir>, TextRange)>,
+    stcs: HashMap<'ir, StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
-    dyns: Vec<'ir, (IrRef<'id, 'ir>, IrRef<'id, 'ir>, TextRange)>,
+    dyns: Vec<
+        'ir,
+        (
+            GhostRoIrRef<'id, 'ir>,
+            GhostRoMaybeThunkRef<'id, 'ir>,
+            TextRange,
+        ),
+    >,
 }
 
 fn downgrade_attrs<'id, 'ir>(
@@ -862,22 +942,22 @@ fn downgrade_attrs<'id, 'ir>(
 fn downgrade_attr<'id, 'ir>(
     attr: ast::Attr,
     ctx: &mut impl DowngradeContext<'id, 'ir>,
-) -> Result<Attr<IrRef<'id, 'ir>>> {
+) -> Result<Attr<GhostRoIrRef<'id, 'ir>>> {
     use ast::Attr::*;
     use ast::InterpolPart::*;
     match attr {
         Ident(ident) => Ok(Attr::Str(
-            ctx.new_sym(ident.to_string()),
+            ctx.intern_string(ident.to_string()),
             ident.syntax().text_range(),
         )),
         Str(string) => {
             let parts = string.normalized_parts();
             let span = string.syntax().text_range();
             if parts.is_empty() {
-                Ok(Attr::Str(ctx.new_sym("".to_string()), span))
+                Ok(Attr::Str(ctx.intern_string(""), span))
             } else if parts.len() == 1 {
                 match parts.into_iter().next().expect("len checked") {
-                    Literal(ident) => Ok(Attr::Str(ctx.new_sym(ident), span)),
+                    Literal(ident) => Ok(Attr::Str(ctx.intern_string(ident), span)),
                     Interpolation(interpol) => Ok(Attr::Dynamic(
                         interpol
                             .expr()
@@ -891,7 +971,10 @@ fn downgrade_attr<'id, 'ir>(
                 let parts = parts
                     .into_iter()
                     .map(|part| match part {
-                        Literal(lit) => Ok(ctx.new_expr(Ir::Str(lit.box_in(bump)))),
+                        Literal(lit) => {
+                            let id = ctx.intern_string(lit);
+                            Ok(ctx.new_expr(Ir::Str(id)))
+                        }
                         Interpolation(interpol) => interpol
                             .expr()
                             .require(ctx, interpol.syntax().text_range())?
@@ -920,7 +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()
@@ -929,24 +1012,22 @@ fn downgrade_attrpath<'id, 'ir>(
 }
 
 struct PatternBindings<'id, 'ir> {
-    body: IrRef<'id, 'ir>,
+    body: GhostRoIrRef<'id, 'ir>,
-    required: Vec<'ir, (SymId, TextRange)>,
+    required: Vec<'ir, (StringId, TextRange)>,
-    optional: Vec<'ir, (SymId, TextRange)>,
+    optional: Vec<'ir, (StringId, TextRange)>,
 }
 
 fn downgrade_pattern_bindings<'id, 'ir, Ctx>(
     pat_entries: impl Iterator<Item = ast::PatEntry>,
-    alias: Option<SymId>,
+    alias: Option<StringId>,
-    arg: ArgId,
     ctx: &mut Ctx,
-    body_fn: impl FnOnce(&mut Ctx, &[SymId]) -> Result<IrRef<'id, 'ir>>,
+    body_fn: impl FnOnce(&mut Ctx, &[StringId]) -> Result<GhostRoIrRef<'id, 'ir>>,
 ) -> Result<PatternBindings<'id, 'ir>>
 where
     Ctx: DowngradeContext<'id, 'ir>,
 {
-    let arg = ctx.new_expr(Ir::Arg(arg));
     struct Param {
-        sym: SymId,
+        sym: StringId,
         sym_span: TextRange,
         default: Option<ast::Expr>,
         span: TextRange,
@@ -958,13 +1039,13 @@ where
     for entry in pat_entries {
         let ident = entry.ident().require(ctx, entry.syntax().text_range())?;
         let sym_span = ident.syntax().text_range();
-        let sym = ctx.new_sym(ident.syntax().text().to_string());
+        let sym = ctx.intern_string(ident.syntax().text().to_string());
         let default = entry.default();
         let span = entry.syntax().text_range();
 
         if !seen_params.insert(sym) {
             return Err(Error::downgrade_error(
-                format!("duplicate parameter '{}'", ctx.get_sym(sym)),
+                format!("duplicate parameter '{}'", ctx.resolve_sym(sym)),
                 ctx.get_current_source(),
                 span,
             ));
@@ -998,6 +1079,8 @@ 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()
@@ -1008,21 +1091,17 @@ where
                     default,
                     span,
                 } = param;
-                let default = if let Some(default) = default {
+                let default = default.map(|default| default.downgrade(ctx)).transpose()?;
-                    let default = default.clone().downgrade(ctx)?;
-                    Some(ctx.maybe_thunk(default))
-                } else {
-                    None
-                };
 
-                Ok(ctx.new_expr(Ir::Select {
+                let expr = ctx.new_expr(Ir::Select {
                     expr: arg,
                     attrpath: Vec::from_iter_in([Attr::Str(sym, sym_span)], bump),
                     default,
                     span,
-                }))
+                });
+                Ok(ctx.maybe_thunk(expr))
             })
-            .chain(alias.into_iter().map(|_| Ok(arg)))
+            .chain(alias.into_iter().map(|_| Ok(arg_thunk)))
             .collect_in::<Result<_>>(bump)?;
 
         let body = body_fn(ctx, &keys)?;
@@ -1042,10 +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, &[SymId]) -> 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)
@@ -1055,7 +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>,
 {
@@ -1076,14 +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,
-        &[SymId],
+        &[StringId],
-        &[(IrRef<'id, 'ir>, IrRef<'id, 'ir>, TextRange)],
+        &[(
-    ) -> Result<IrRef<'id, 'ir>>,
+            GhostRoIrRef<'id, 'ir>,
+            GhostRoMaybeThunkRef<'id, 'ir>,
+            TextRange,
+        )],
+    ) -> Result<GhostRoIrRef<'id, 'ir>>,
 {
     let mut pending = PendingAttrSet::new_in(ctx.bump());
     pending.collect_entries(entries.iter().cloned(), ctx)?;
@@ -1095,18 +1178,21 @@ where
 
     ctx.with_let_scope(&keys, |ctx| {
         let finalized = finalize_pending_set::<_, ALLOW_DYN>(pending, &inherit_lookups, ctx)?;
-        let vals = keys
+        let vals = {
-            .iter()
+            let mut temp = Vec::with_capacity_in(keys.len(), ctx.bump());
-            .map(|sym| finalized.stcs.get(sym).expect("WTF").0)
+            for sym in &keys {
-            .collect_in(ctx.bump());
+                temp.push(finalized.stcs.get(sym).expect("WTF").0);
+            }
+            temp
+        };
         body_fn(ctx, &keys, &finalized.dyns).map(|body| (vals, body))
     })
 }
 
-fn collect_inherit_lookups<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>>(
+fn collect_inherit_lookups<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>>(
     entries: &[ast::Entry],
     ctx: &mut Ctx,
-) -> Result<HashMap<'ir, SymId, (IrRef<'id, 'ir>, TextRange)>> {
+) -> Result<HashMap<'ir, StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>> {
     let mut inherit_lookups = HashMap::new_in(ctx.bump());
     for entry in entries {
         if let ast::Entry::Inherit(inherit) = entry
@@ -1115,7 +1201,7 @@ fn collect_inherit_lookups<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>>(
             for attr in inherit.attrs() {
                 if let ast::Attr::Ident(ident) = attr {
                     let attr_span = ident.syntax().text_range();
-                    let sym = ctx.new_sym(ident.to_string());
+                    let sym = ctx.intern_string(ident.to_string());
                     let expr = ctx.lookup(sym, attr_span)?;
                     inherit_lookups.insert(sym, (expr, attr_span));
                 }
@@ -1128,13 +1214,13 @@ fn collect_inherit_lookups<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>>(
 fn collect_binding_syms<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_DYN: bool>(
     pending: &PendingAttrSet,
     ctx: &mut Ctx,
-) -> Result<HashSet<SymId>> {
+) -> Result<HashSet<StringId>> {
     let mut binding_syms = HashSet::new();
 
     for (sym, (_, span)) in &pending.stcs {
         if !binding_syms.insert(*sym) {
             return Err(Error::downgrade_error(
-                format!("attribute '{}' already defined", ctx.get_sym(*sym)),
+                format!("attribute '{}' already defined", ctx.resolve_sym(*sym)),
                 ctx.get_current_source(),
                 *span,
             ));
@@ -1146,15 +1232,15 @@ fn collect_binding_syms<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, const AL
 
 fn finalize_pending_set<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_DYN: bool>(
     pending: PendingAttrSet,
-    inherit_lookups: &HashMap<SymId, (IrRef<'id, 'ir>, TextRange)>,
+    inherit_lookups: &HashMap<StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
     ctx: &mut Ctx,
 ) -> Result<FinalizedAttrSet<'id, 'ir>> {
     let mut stcs = HashMap::new_in(ctx.bump());
     let mut dyns = Vec::new_in(ctx.bump());
 
     for (sym, (value, value_span)) in pending.stcs {
-        let expr_id = finalize_pending_value::<_, ALLOW_DYN>(value, inherit_lookups, ctx)?;
+        let expr = finalize_pending_value::<_, ALLOW_DYN>(value, inherit_lookups, ctx)?;
-        stcs.insert(sym, (expr_id, value_span));
+        stcs.insert(sym, (ctx.maybe_thunk(expr), value_span));
     }
 
     if ALLOW_DYN {
@@ -1162,12 +1248,10 @@ fn finalize_pending_set<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_D
             let key_id = downgrade_attr(attr, ctx)?;
             let key_expr = match key_id {
                 Attr::Dynamic(id, _) => id,
-                Attr::Str(sym, _attr_span) => {
+                Attr::Str(sym, _attr_span) => ctx.new_expr(Ir::Str(sym)),
-                    ctx.new_expr(Ir::Str(ctx.get_sym(sym).to_string().box_in(ctx.bump())))
-                }
             };
-            let value_id = finalize_pending_value::<_, ALLOW_DYN>(value, inherit_lookups, ctx)?;
+            let value = finalize_pending_value::<_, ALLOW_DYN>(value, inherit_lookups, ctx)?;
-            dyns.push((key_expr, value_id, value_span));
+            dyns.push((key_expr, ctx.maybe_thunk(value), value_span));
         }
     }
 
@@ -1176,30 +1260,26 @@ fn finalize_pending_set<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_D
 
 fn finalize_pending_value<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_DYN: bool>(
     value: PendingValue,
-    inherit_lookups: &HashMap<SymId, (IrRef<'id, 'ir>, TextRange)>,
+    inherit_lookups: &HashMap<StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
     ctx: &mut Ctx,
-) -> Result<IrRef<'id, 'ir>> {
+) -> Result<GhostRoIrRef<'id, 'ir>> {
     match value {
-        PendingValue::Expr(expr) => {
+        PendingValue::Expr(expr) => expr.downgrade(ctx),
-            let id = Downgrade::downgrade(expr, ctx)?;
-            Ok(ctx.maybe_thunk(id))
-        }
         PendingValue::InheritFrom(from_expr, sym, span) => {
-            let from_id = Downgrade::downgrade(from_expr, ctx)?;
+            let from = Downgrade::downgrade(from_expr, ctx)?;
-            let select_id = ctx.new_expr(Ir::Select {
+            Ok(ctx.new_expr(Ir::Select {
-                expr: from_id,
+                expr: from,
                 attrpath: Vec::from_iter_in([Attr::Str(sym, span)], ctx.bump()),
                 default: None,
                 span,
-            });
+            }))
-            Ok(ctx.maybe_thunk(select_id))
         }
         PendingValue::InheritScope(sym, span) => {
             if let Some(&(expr, _)) = inherit_lookups.get(&sym) {
-                Ok(ctx.maybe_thunk(expr))
+                Ok(ctx.new_expr(Ir::MaybeThunk(expr)))
             } else {
-                let lookup_id = ctx.lookup(sym, span)?;
+                ctx.lookup(sym, span)
-                Ok(ctx.maybe_thunk(lookup_id))
+                    .map(|val| ctx.new_expr(Ir::MaybeThunk(val)))
             }
         }
         PendingValue::Set(set) => {
@@ -1221,15 +1301,15 @@ fn finalize_pending_value<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW
 
 fn downgrade_path<'id, 'ir>(
     parts: impl IntoIterator<Item = ast::InterpolPart<ast::PathContent>>,
-    _span: rnix::TextRange,
     ctx: &mut impl DowngradeContext<'id, 'ir>,
-) -> Result<IrRef<'id, 'ir>> {
+) -> Result<GhostRoIrRef<'id, 'ir>> {
     let bump = ctx.bump();
     let parts = parts
         .into_iter()
         .map(|part| match part {
             ast::InterpolPart::Literal(lit) => {
-                Ok(ctx.new_expr(Ir::Str(lit.text().to_string().box_in(ctx.bump()))))
+                let id = ctx.intern_string(lit.text());
+                Ok(ctx.new_expr(Ir::Str(id)))
             }
             ast::InterpolPart::Interpolation(interpol) => interpol
                 .expr()

fix-ir/src/lib.rs

@@ -0,0 +1,332 @@
+use std::hash::Hash;
+use std::marker::PhantomData;
+
+use bumpalo::Bump;
+use bumpalo::collections::Vec;
+use fix_builtins::{BUILTINS, BuiltinId};
+use fix_common::StringId;
+use ghost_cell::{GhostCell, GhostToken};
+use num_enum::TryFromPrimitive as _;
+use rnix::{TextRange, ast};
+use string_interner::DefaultStringInterner;
+
+pub mod downgrade;
+
+pub type HashMap<'ir, K, V> = hashbrown::HashMap<K, V, hashbrown::DefaultHashBuilder, &'ir Bump>;
+
+pub type GhostIrRef<'id, 'ir> = <GhostRef<'id, 'ir> as RefExt<'ir>>::IrRef;
+pub type GhostRoIrRef<'id, 'ir> = <GhostRoRef<'id, 'ir> as RefExt<'ir>>::IrRef;
+pub type RawIrRef<'ir> = <RawRef<'ir> as RefExt<'ir>>::IrRef;
+pub type GhostMaybeThunkRef<'id, 'ir> = <GhostRef<'id, 'ir> as RefExt<'ir>>::MaybeThunkRef;
+pub type GhostRoMaybeThunkRef<'id, 'ir> = <GhostRoRef<'id, 'ir> as RefExt<'ir>>::MaybeThunkRef;
+
+impl<'id, 'ir> Ir<'ir, GhostRoRef<'id, 'ir>> {
+    /// Freeze a mutable IR reference into a read-only one, consuming the
+    /// `GhostToken` to prevent any further mutation.
+    pub fn freeze(this: GhostRoIrRef<'id, 'ir>, _: GhostToken<'id>) -> RawIrRef<'ir> {
+        // SAFETY: The transmute is sound because:
+        // - `GhostCell<'id, T>` is `#[repr(transparent)]` over `T`, so
+        //   `&'ir GhostCell<'id, T>` and `&'ir T` have identical layout.
+        // - `Ir<'ir, R>` is `#[repr(C)]`, and for every field that depends on
+        //   `R`, instantiating `R = GhostRef<'id, 'ir>` vs `R = RawRef<'ir>`
+        //   produces types of identical layout:
+        //     - `R::IrRef` becomes `&'ir GhostCell<'id, Ir<...>>` vs `&'ir Ir<...>`
+        //     - `R::MaybeThunkRef` becomes `&'ir GhostCell<'id, MaybeThunk>`
+        //       vs `&'ir MaybeThunk`
+        //     - `R::Ref<Ir<'ir, R>>` (used in `ConcatStrings::parts`) reduces
+        //       to the same case as `R::IrRef`
+        // - Therefore `IrRef<'id, 'ir>` and `RawIrRef<'ir>` are both
+        //   pointer-sized references with the same layout.
+        //
+        // Consuming the `GhostToken` guarantees no `borrow_mut` calls can
+        // occur afterwards, so the shared `&Ir` references reachable from a
+        // `RawIrRef<'ir>` can never alias with mutable references.
+        unsafe { std::mem::transmute::<GhostRoIrRef<'id, 'ir>, RawIrRef<'ir>>(this) }
+    }
+}
+
+#[repr(transparent)]
+pub struct GhostRoCell<'id, T: ?Sized>(GhostCell<'id, T>);
+
+impl<'id, T> From<GhostCell<'id, T>> for GhostRoCell<'id, T> {
+    fn from(value: GhostCell<'id, T>) -> Self {
+        Self(value)
+    }
+}
+
+impl<'id, T: ?Sized> From<&GhostCell<'id, T>> for &GhostRoCell<'id, T> {
+    fn from(value: &GhostCell<'id, T>) -> Self {
+        // SAFETY: `GhostRoCell` is `#[repr(transparent)]` over `GhostCell`
+        // TODO: document mutability
+        unsafe { std::mem::transmute(value) }
+    }
+}
+
+impl<'id, T: ?Sized> From<&T> for &GhostRoCell<'id, T> {
+    fn from(value: &T) -> Self {
+        // SAFETY: `GhostRoCell` is `#[repr(transparent)]` over `GhostCell`,
+        //         which is `#[repr(transparent)]` over `T`
+        // TODO: document mutability
+        unsafe { std::mem::transmute(value) }
+    }
+}
+
+impl<'id, T: ?Sized> GhostRoCell<'id, T> {
+    pub fn borrow<'a>(&'a self, token: &'a GhostToken<'id>) -> &'a T {
+        self.0.borrow(token)
+    }
+}
+
+#[repr(C)]
+#[derive(Debug, Clone, Copy)]
+pub enum MaybeThunk {
+    Int(i64),
+    Float(f64),
+    Bool(bool),
+    Null,
+    Str(StringId),
+    Path(StringId),
+    Thunk(ThunkId),
+    Arg { layer: u8 },
+    Builtin(BuiltinId),
+    BuiltinConst(StringId),
+    Builtins,
+    ReplBinding(StringId),
+    ScopedImportBinding(StringId),
+}
+
+pub trait Ref<'ir> {
+    type Ref<T>
+    where
+        T: 'ir;
+}
+
+pub trait RefExt<'ir>: Ref<'ir> {
+    type Ir;
+    type IrRef;
+    type MaybeThunkRef;
+}
+impl<'ir, T: Ref<'ir> + 'ir> RefExt<'ir> for T {
+    type Ir = Ir<'ir, Self>;
+    type IrRef = Self::Ref<Self::Ir>;
+    type MaybeThunkRef = Self::Ref<MaybeThunk>;
+}
+
+pub struct GhostRef<'id, 'ir>(PhantomData<&'ir GhostCell<'id, ()>>);
+pub struct GhostRoRef<'id, 'ir>(PhantomData<&'ir GhostRoCell<'id, ()>>);
+pub struct RawRef<'ir>(PhantomData<&'ir ()>);
+
+impl<'id, 'ir> Ref<'ir> for GhostRef<'id, 'ir> {
+    type Ref<T: 'ir> = &'ir GhostCell<'id, T>;
+}
+impl<'id, 'ir> Ref<'ir> for GhostRoRef<'id, 'ir> {
+    type Ref<T: 'ir> = &'ir GhostRoCell<'id, T>;
+}
+impl<'ir> Ref<'ir> for RawRef<'ir> {
+    type Ref<T: 'ir> = &'ir T;
+}
+
+#[repr(C)]
+#[derive(Debug)]
+pub enum Ir<'ir, R: RefExt<'ir> + ?Sized + 'ir> {
+    Int(i64),
+    Float(f64),
+    Bool(bool),
+    Null,
+    Str(StringId),
+    Path(R::IrRef),
+    AttrSet {
+        stcs: HashMap<'ir, StringId, (R::MaybeThunkRef, TextRange)>,
+        dyns: Vec<'ir, (R::IrRef, R::MaybeThunkRef, TextRange)>,
+    },
+    List {
+        items: Vec<'ir, R::MaybeThunkRef>,
+    },
+    ConcatStrings {
+        parts: Vec<'ir, R::Ref<Ir<'ir, R>>>,
+        force_string: bool,
+    },
+
+    // OPs
+    UnOp {
+        rhs: R::IrRef,
+        kind: UnOpKind,
+    },
+    BinOp {
+        lhs: R::IrRef,
+        rhs: R::IrRef,
+        kind: BinOpKind,
+    },
+    HasAttr {
+        lhs: R::IrRef,
+        rhs: Vec<'ir, Attr<R::IrRef>>,
+    },
+    Select {
+        expr: R::IrRef,
+        attrpath: Vec<'ir, Attr<R::IrRef>>,
+        default: Option<R::IrRef>,
+        span: TextRange,
+    },
+
+    // Conditionals
+    If {
+        cond: R::IrRef,
+        consq: R::IrRef,
+        alter: R::IrRef,
+    },
+    Assert {
+        assertion: R::IrRef,
+        expr: R::IrRef,
+        assertion_raw: String,
+        span: TextRange,
+    },
+
+    WithLookup {
+        sym: StringId,
+        namespaces: Vec<'ir, R::MaybeThunkRef>,
+    },
+
+    // Function related
+    Func {
+        body: R::IrRef,
+        param: Option<Param<'ir>>,
+        thunks: Vec<'ir, (ThunkId, R::IrRef)>,
+    },
+    Arg {
+        layer: u8,
+    },
+    Call {
+        func: R::IrRef,
+        arg: R::MaybeThunkRef,
+        span: TextRange,
+    },
+
+    // Builtins
+    Builtins,
+    Builtin(BuiltinId),
+    BuiltinConst(StringId),
+
+    // Misc
+    TopLevel {
+        body: R::IrRef,
+        thunks: Vec<'ir, (ThunkId, R::IrRef)>,
+    },
+    MaybeThunk(R::MaybeThunkRef),
+    ReplBinding(StringId),
+    ScopedImportBinding(StringId),
+}
+
+#[repr(transparent)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct ThunkId(pub usize);
+
+#[repr(transparent)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct SpanId(pub u32);
+
+/// Represents a key in an attribute path.
+#[allow(unused)]
+#[derive(Debug)]
+pub enum Attr<Ref> {
+    /// A dynamic attribute key, which is an expression that must evaluate to a string.
+    /// Example: `attrs.${key}`
+    Dynamic(Ref, TextRange),
+    /// A static attribute key.
+    /// Example: `attrs.key`
+    Str(StringId, TextRange),
+}
+
+/// The kinds of binary operations supported in Nix.
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
+pub enum BinOpKind {
+    // Arithmetic
+    Add,
+    Sub,
+    Div,
+    Mul,
+
+    // Comparison
+    Eq,
+    Neq,
+    Lt,
+    Gt,
+    Leq,
+    Geq,
+
+    // Logical
+    And,
+    Or,
+    Impl,
+
+    // Set/String/Path operations
+    Con, // List concatenation (`++`)
+    Upd, // AttrSet update (`//`)
+}
+
+/// The kinds of unary operations.
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
+pub enum UnOpKind {
+    Neg, // Negation (`-`)
+    Not, // Logical not (`!`)
+}
+
+impl From<ast::UnaryOpKind> for UnOpKind {
+    fn from(value: ast::UnaryOpKind) -> Self {
+        match value {
+            ast::UnaryOpKind::Invert => UnOpKind::Not,
+            ast::UnaryOpKind::Negate => UnOpKind::Neg,
+        }
+    }
+}
+
+/// Describes the parameters of a function.
+#[derive(Debug)]
+pub struct Param<'ir> {
+    pub required: Vec<'ir, (StringId, TextRange)>,
+    pub optional: Vec<'ir, (StringId, TextRange)>,
+    pub ellipsis: bool,
+}
+
+pub fn new_global_env(
+    strings: &mut DefaultStringInterner,
+) -> hashbrown::HashMap<StringId, MaybeThunk> {
+    let mut global_env = hashbrown::HashMap::new();
+    let builtins_sym = StringId(strings.get_or_intern("builtins"));
+    global_env.insert(builtins_sym, MaybeThunk::Builtins);
+
+    for (idx, &(name, _)) in BUILTINS.iter().enumerate() {
+        let id = BuiltinId::try_from_primitive(idx as u8).expect("infallible");
+        let name = StringId(strings.get_or_intern(name));
+        global_env.insert(name, MaybeThunk::Builtin(id));
+    }
+
+    let consts = [
+        (
+            "__currentSystem",
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("currentSystem"))),
+        ),
+        ("__langVersion", MaybeThunk::Int(6)),
+        (
+            "__nixVersion",
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("nixVersion"))),
+        ),
+        (
+            "__storeDir",
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("storeDir"))),
+        ),
+        (
+            "__nixPath",
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("nixPath"))),
+        ),
+        ("null", MaybeThunk::Null),
+        ("true", MaybeThunk::Bool(true)),
+        ("false", MaybeThunk::Bool(false)),
+    ];
+
+    for (name, ir) in consts {
+        let name = StringId(strings.get_or_intern(name));
+        global_env.insert(name, ir);
+    }
+
+    global_env
+}

fix-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

@@ -0,0 +1,24 @@
+[package]
+name = "fix-vm"
+version = "0.1.0"
+edition = "2024"
+
+[features]
+tailcall = []
+
+[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"
+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/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-vm/src/lib.rs

@@ -0,0 +1,694 @@
+#![warn(clippy::unwrap_used)]
+#![cfg_attr(feature = "tailcall", expect(incomplete_features))]
+#![cfg_attr(
+    feature = "tailcall",
+    feature(explicit_tail_calls, rust_preserve_none_cc)
+)]
+
+use std::path::PathBuf;
+
+use fix_builtins::{BUILTINS, BuiltinId};
+use fix_codegen::InstructionPtr;
+use fix_common::StringId;
+use fix_error::{Error, Result, Source};
+use gc_arena::metrics::Pacing;
+use gc_arena::{Arena, Collect, Gc, Mutation, RefLock, Rootable};
+use hashbrown::HashMap;
+use num_enum::TryFromPrimitive;
+use smallvec::SmallVec;
+
+#[cfg(feature = "tailcall")]
+mod dispatch_tailcall;
+pub use fix_abstract_vm::*;
+mod instructions;
+
+type VmResult<T> = std::result::Result<T, VmError>;
+
+#[derive(Collect)]
+#[collect(no_drop)]
+pub struct Vm<'gc> {
+    stack: Vec<Value<'gc>>,
+    call_stack: Vec<CallFrame<'gc>>,
+    call_depth: usize,
+    #[allow(dead_code)]
+    #[collect(require_static)]
+    error_context: Vec<ErrorFrame>,
+
+    env: GcEnv<'gc>,
+
+    import_cache: HashMap<PathBuf, Value<'gc>>,
+    scope_slots: Vec<Value<'gc>>,
+
+    builtins: Value<'gc>,
+    empty_list: Value<'gc>,
+    empty_attrs: Value<'gc>,
+
+    force_mode: ForceMode,
+
+    #[collect(require_static)]
+    result: Option<Result<fix_common::Value>>,
+
+    #[collect(require_static)]
+    pending_load: Option<PendingLoad>,
+
+    functor_sym: StringId,
+}
+
+fn init_builtins<'gc>(mc: &Mutation<'gc>, ctx: &mut impl VmRuntimeCtx) -> Value<'gc> {
+    let mut entries = SmallVec::with_capacity(BUILTINS.len());
+
+    for (idx, &(name, arity)) in BUILTINS.iter().enumerate() {
+        let id = BuiltinId::try_from_primitive(idx as u8).expect("infallible");
+        let name = name.strip_prefix("__").unwrap_or(name);
+        let name = ctx.intern_string(name);
+        let dispatch_ip = id.entry_phase().ip();
+        entries.push((
+            name,
+            Value::new_inline(PrimOp {
+                id,
+                arity,
+                dispatch_ip,
+            }),
+        ));
+    }
+
+    let consts = [
+        (
+            "__currentSystem",
+            Value::new_inline(ctx.intern_string("x86_64-linux")),
+        ),
+        ("__langVersion", Value::new_inline(6i32)),
+        (
+            "__nixVersion",
+            Value::new_inline(ctx.intern_string("2.24.0")),
+        ),
+        (
+            "__storeDir",
+            Value::new_inline(ctx.intern_string("/nix/store")),
+        ),
+        ("__nixPath", Value::new_gc(Gc::new(mc, List::default()))),
+        ("null", Value::new_inline(Null)),
+        ("true", Value::new_inline(true)),
+        ("false", Value::new_inline(false)),
+    ];
+
+    for (name, val) in consts {
+        let name = name.strip_prefix("__").unwrap_or(name);
+        let name = ctx.intern_string(name);
+        entries.push((name, val));
+    }
+
+    let self_ref_thunk = Gc::new(mc, RefLock::new(ThunkState::Blackhole));
+    let sym = ctx.intern_string("builtins");
+    entries.push((sym, Value::new_gc(self_ref_thunk)));
+
+    entries.sort_by_key(|(k, _)| *k);
+
+    let builtins_set = Gc::new(mc, AttrSet::from_sorted_unchecked(entries));
+    let builtins_value = Value::new_gc(builtins_set);
+    *self_ref_thunk.borrow_mut(mc) =
+        ThunkState::Evaluated(builtins_value.restrict().expect("builtins is not a thunk"));
+    builtins_value
+}
+
+impl<'gc> Vm<'gc> {
+    fn new(force_mode: ForceMode, mc: &Mutation<'gc>, ctx: &mut impl VmRuntimeCtx) -> Self {
+        let builtins = init_builtins(mc, ctx);
+        Vm {
+            stack: Vec::with_capacity(8192),
+            call_stack: Vec::with_capacity(1024),
+            call_depth: 0,
+            error_context: Vec::with_capacity(1024),
+
+            env: Gc::new(mc, RefLock::new(Env::empty())),
+
+            import_cache: HashMap::new(),
+            scope_slots: Vec::new(),
+
+            builtins,
+            empty_list: Value::new_gc(Gc::new(mc, List::default())),
+            empty_attrs: Value::new_gc(Gc::new(mc, AttrSet::default())),
+
+            force_mode,
+
+            result: None,
+            pending_load: None,
+
+            functor_sym: ctx.intern_string("__functor"),
+        }
+    }
+
+    #[inline(always)]
+    fn finish_ok(&mut self, val: fix_common::Value) -> Step {
+        self.result = Some(Ok(val));
+        Step::Break(Break::Done)
+    }
+
+    #[inline(always)]
+    fn finish_err(&mut self, err: Box<Error>) -> Step {
+        self.result = Some(Err(err));
+        Step::Break(Break::Done)
+    }
+
+    #[inline(always)]
+    fn finish_type_err(&mut self, expected: NixType, got: NixType) -> Step {
+        self.result = Some(Err(Error::eval_error(format!(
+            "expected {expected}, got {got}"
+        ))));
+        Step::Break(Break::Done)
+    }
+
+    #[inline(always)]
+    fn finish_vm_err(&mut self, err: VmError) -> Step {
+        self.finish_err(err.into_error())
+    }
+
+    #[inline(always)]
+    fn push(&mut self, val: Value<'gc>) {
+        self.stack.push(val);
+    }
+
+    #[inline(always)]
+    #[must_use]
+    fn pop(&mut self) -> Value<'gc> {
+        self.stack.pop().expect("stack underflow")
+    }
+
+    #[inline(always)]
+    #[must_use]
+    fn peek(&self, depth: usize) -> Value<'gc> {
+        *self
+            .stack
+            .get(self.stack.len() - depth - 1)
+            .expect("stack underflow")
+    }
+
+    #[inline(always)]
+    #[must_use]
+    fn peek_forced(&self, depth: usize) -> StrictValue<'gc> {
+        self.stack
+            .get(self.stack.len() - depth - 1)
+            .expect("stack underflow")
+            .restrict()
+            .expect("forced")
+    }
+
+    #[inline(always)]
+    fn replace(&mut self, depth: usize, val: Value<'gc>) {
+        let len = self.stack.len();
+        *self
+            .stack
+            .get_mut(len - depth - 1)
+            .expect("stack underflow") = val;
+    }
+
+    #[inline(always)]
+    #[cfg_attr(debug_assertions, track_caller)]
+    fn pop_forced(&mut self) -> StrictValue<'gc> {
+        self.stack
+            .pop()
+            .expect("stack underflow")
+            .restrict()
+            .expect("forced")
+    }
+
+    /// 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.  Calling `force_and_retry` twice (or more)
+    ///   means the handler will be re-run from the top after each retry;
+    ///   any stack modifications between the two calls would be duplicated
+    ///   and corrupt the stack layout.
+    ///
+    /// * The caller must ensure that the stack layout at the point of
+    ///   invocation is **identical** every time the handler is re-entered.
+    ///   In practice this means no pushes, pops, or local mutations may
+    ///   happen before the call, and the call must be the first thing
+    ///   that consumes the instruction's operand values.
+    ///
+    /// * The return value must be propagated with `?` so that
+    ///   `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>,
+    ) -> std::ops::ControlFlow<Break, T> {
+        self.force_and_retry_pc(reader, mc, reader.inst_start_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,
+    ) -> std::ops::ControlFlow<Break, T> {
+        T::force_and_check(self, reader, mc, 0, resume_pc)?;
+        std::ops::ControlFlow::Continue(T::pop_converted(self))
+    }
+
+    #[inline(always)]
+    #[allow(unused)]
+    fn force_slot(
+        &mut self,
+        depth: usize,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        self.force_slot_to_pc(depth, reader, mc, reader.inst_start_pc())
+    }
+
+    #[inline(always)]
+    fn force_slot_to_pc(
+        &mut self,
+        depth: usize,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        resume_pc: usize,
+    ) -> Step {
+        let Some(thunk) = self.peek(depth).as_gc::<Thunk>() else {
+            return Step::Continue(());
+        };
+        let mut state = thunk.borrow_mut(mc);
+        match *state {
+            ThunkState::Pending { ip, env } => {
+                *state = ThunkState::Blackhole;
+                self.call_stack.push(CallFrame {
+                    thunk: Some(thunk),
+                    pc: resume_pc,
+                    env: self.env,
+                });
+                self.env = env;
+                reader.set_pc(ip);
+                Step::Break(Break::Force)
+            }
+            ThunkState::Evaluated(v) => {
+                self.replace(depth, v.relax());
+                Step::Continue(())
+            }
+            ThunkState::Apply { func, arg } => {
+                self.call_stack.push(CallFrame {
+                    thunk: Some(thunk),
+                    pc: resume_pc,
+                    env: self.env,
+                });
+                self.push(func);
+                self.call(reader, mc, arg, resume_pc)
+            }
+            ThunkState::Blackhole => {
+                self.finish_err(Error::eval_error("infinite recursion encountered"))
+            }
+        }
+    }
+}
+
+impl<'gc> Machine<'gc> for Vm<'gc> {
+    #[inline(always)]
+    fn push(&mut self, val: Value<'gc>) {
+        self.push(val);
+    }
+
+    #[inline(always)]
+    fn pop(&mut self) -> Value<'gc> {
+        self.pop()
+    }
+
+    #[inline(always)]
+    fn peek(&self, depth: usize) -> Value<'gc> {
+        Vm::peek(self, depth)
+    }
+
+    #[inline(always)]
+    fn peek_forced(&self, depth: usize) -> StrictValue<'gc> {
+        Vm::peek_forced(self, depth)
+    }
+
+    #[inline(always)]
+    fn pop_forced(&mut self) -> StrictValue<'gc> {
+        self.pop_forced()
+    }
+
+    #[inline(always)]
+    fn replace(&mut self, depth: usize, val: Value<'gc>) {
+        self.replace(depth, val);
+    }
+
+    #[inline(always)]
+    fn stack_len(&self) -> usize {
+        self.stack.len()
+    }
+
+    #[inline(always)]
+    fn force_slot_to_pc(
+        &mut self,
+        depth: usize,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        resume_pc: usize,
+    ) -> Step {
+        self.force_slot_to_pc(depth, reader, mc, resume_pc)
+    }
+
+    #[inline(always)]
+    fn call(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+        arg: Value<'gc>,
+        resume_pc: usize,
+    ) -> Step {
+        self.call(reader, mc, arg, resume_pc)
+    }
+
+    #[inline(always)]
+    fn push_call_frame(&mut self, frame: CallFrame<'gc>) {
+        self.call_stack.push(frame);
+    }
+
+    #[inline(always)]
+    fn pop_call_frame(&mut self) -> Option<CallFrame<'gc>> {
+        self.call_stack.pop()
+    }
+
+    #[inline(always)]
+    fn call_depth(&self) -> usize {
+        self.call_depth
+    }
+
+    #[inline(always)]
+    fn inc_call_depth(&mut self) {
+        self.call_depth += 1;
+    }
+
+    #[inline(always)]
+    fn dec_call_depth(&mut self) {
+        self.call_depth -= 1;
+    }
+
+    #[inline(always)]
+    fn env(&self) -> GcEnv<'gc> {
+        self.env
+    }
+
+    #[inline(always)]
+    fn set_env(&mut self, env: GcEnv<'gc>) {
+        self.env = env;
+    }
+
+    #[inline(always)]
+    fn finish_ok(&mut self, val: fix_common::Value) -> Step {
+        self.finish_ok(val)
+    }
+
+    #[inline(always)]
+    fn finish_err(&mut self, err: Box<Error>) -> Step {
+        self.finish_err(err)
+    }
+
+    #[inline(always)]
+    fn finish_type_err(&mut self, expected: NixType, got: NixType) -> Step {
+        self.finish_type_err(expected, got)
+    }
+
+    #[inline(always)]
+    fn builtins(&self) -> Value<'gc> {
+        self.builtins
+    }
+
+    #[inline(always)]
+    fn functor_sym(&self) -> StringId {
+        self.functor_sym
+    }
+
+    #[inline(always)]
+    fn empty_list(&self) -> Value<'gc> {
+        self.empty_list
+    }
+
+    #[inline(always)]
+    fn empty_attrs(&self) -> Value<'gc> {
+        self.empty_attrs
+    }
+
+    #[inline(always)]
+    fn force_mode(&self) -> ForceMode {
+        self.force_mode
+    }
+
+    #[inline(always)]
+    fn import_cache_get(&self, path: &std::path::Path) -> Option<Value<'gc>> {
+        self.import_cache.get(path).copied()
+    }
+
+    #[inline(always)]
+    fn import_cache_insert(&mut self, path: PathBuf, val: Value<'gc>) {
+        self.import_cache.insert(path, val);
+    }
+
+    #[inline(always)]
+    fn scope_slot(&self, idx: u32) -> Value<'gc> {
+        *self
+            .scope_slots
+            .get(idx as usize)
+            .expect("invalid scope slot")
+    }
+
+    #[inline(always)]
+    fn scope_slots_push(&mut self, val: Value<'gc>) -> u32 {
+        let idx = self.scope_slots.len() as u32;
+        self.scope_slots.push(val);
+        idx
+    }
+
+    #[inline(always)]
+    fn set_pending_load(&mut self, load: PendingLoad) {
+        self.pending_load = Some(load);
+    }
+}
+
+enum Action {
+    Continue { pc: usize },
+    Done(Result<fix_common::Value>),
+    LoadFile(PendingLoad),
+}
+
+/// Compute initial heap size mirroring CppNix's strategy: 25% of physical RAM,
+/// clamped to [32 MiB, 384 MiB]. Used as `Pacing::min_sleep` so the collector
+/// defers the first cycle until the heap reaches this size.
+fn initial_heap_size() -> usize {
+    const MIN_SIZE: usize = 32 * 1024 * 1024;
+    const MAX_SIZE: usize = 384 * 1024 * 1024;
+
+    let mut sys = sysinfo::System::new();
+    sys.refresh_memory();
+    let total = sys.total_memory() as usize;
+    let quarter = total / 4;
+    quarter.clamp(MIN_SIZE, MAX_SIZE)
+}
+
+impl Vm<'_> {
+    pub fn run<C: VmContext>(
+        ctx: &mut C,
+        ip: InstructionPtr,
+        force_mode: ForceMode,
+    ) -> Result<fix_common::Value> {
+        let (code, runtime) = ctx.split();
+        let mut arena: Arena<Rootable![Vm<'_>]> = Arena::new(|mc| Vm::new(force_mode, mc, runtime));
+        arena.metrics().set_pacing(Pacing {
+            min_sleep: initial_heap_size(),
+            ..Pacing::STOP_THE_WORLD
+        });
+
+        let mut pc = ip.0;
+        loop {
+            let bytecode = code.bytecode();
+            match arena.mutate_root(|mc, root| root.dispatch_batch(bytecode, runtime, pc, mc)) {
+                Action::Continue { pc: new_pc } => {
+                    pc = new_pc;
+                    if arena.metrics().allocation_debt() > 0.0 {
+                        arena.finish_cycle();
+                    }
+                }
+                Action::LoadFile(load) => {
+                    let source = match Source::new_file(load.path) {
+                        Ok(src) => src,
+                        Err(err) => break Err(Error::eval_error(format!("import failed: {err}"))),
+                    };
+                    let extra_scope = load.scope.map(|s| ExtraScope::ScopedImport {
+                        keys: s.keys,
+                        slot_id: s.slot_id,
+                    });
+                    let new_ip = match code.compile_with_scope(source, extra_scope, runtime) {
+                        Ok(ip) => ip,
+                        Err(err) => break Err(err),
+                    };
+                    pc = new_ip.0;
+                    arena.mutate_root(|mc, root| {
+                        root.env = Gc::new(mc, RefLock::new(Env::empty()));
+                    });
+                }
+                Action::Done(done) => break done,
+            }
+        }
+    }
+}
+
+impl<'gc> Vm<'gc> {
+    const DEFAULT_FUEL_AMOUNT: u32 = 1024;
+
+    #[inline(always)]
+    fn dispatch_batch<C: VmRuntimeCtx>(
+        &mut self,
+        bytecode: &[u8],
+        ctx: &mut C,
+        pc: usize,
+        mc: &Mutation<'gc>,
+    ) -> Action {
+        #[cfg(not(feature = "tailcall"))]
+        {
+            self.execute_batch(bytecode, ctx, pc, mc)
+        }
+        #[cfg(feature = "tailcall")]
+        {
+            use crate::dispatch_tailcall::{TailResult, run_tailcall};
+            match run_tailcall(self, mc, ctx, bytecode, pc as u32) {
+                TailResult::YieldFuel(new_pc) => Action::Continue {
+                    pc: new_pc as usize,
+                },
+                TailResult::Done => {
+                    Action::Done(self.result.take().expect("TailResult::Done without result"))
+                }
+                TailResult::LoadFile => Action::LoadFile(
+                    self.pending_load
+                        .take()
+                        .expect("TailResult::LoadFile without pending_load"),
+                ),
+            }
+        }
+    }
+
+    #[inline(always)]
+    #[cfg(not(feature = "tailcall"))]
+    fn execute_batch(
+        &mut self,
+        bytecode: &[u8],
+        ctx: &mut impl VmRuntimeCtx,
+        pc: usize,
+        mc: &Mutation<'gc>,
+    ) -> Action {
+        use fix_codegen::Op::*;
+
+        let mut reader = BytecodeReader::new(bytecode, pc);
+        let mut fuel = Self::DEFAULT_FUEL_AMOUNT;
+
+        loop {
+            if fuel == 0 {
+                return Action::Continue { pc: reader.pc() };
+            }
+            fuel -= 1;
+
+            let op = reader.read_op();
+
+            let result = match op {
+                PushSmi => self.op_push_smi(&mut reader),
+                PushBigInt => self.op_push_bigint(&mut reader, mc),
+                PushFloat => self.op_push_float(&mut reader),
+                PushString => self.op_push_string(&mut reader),
+                PushNull => self.op_push_null(),
+                PushTrue => self.op_push_true(),
+                PushFalse => self.op_push_false(),
+
+                LoadLocal => self.op_load_local(&mut reader),
+                LoadOuter => self.op_load_outer(&mut reader),
+                StoreLocal => self.op_store_local(&mut reader, mc),
+                AllocLocals => self.op_alloc_locals(&mut reader, mc),
+
+                MakeThunk => self.op_make_thunk(&mut reader, mc),
+                MakeClosure => self.op_make_closure(&mut reader, mc),
+                MakePatternClosure => self.op_make_pattern_closure(&mut reader, mc),
+
+                Call => self.op_call(ctx, &mut reader, mc),
+                DispatchPrimOp => self.op_dispatch_primop(ctx, &mut reader, mc),
+                Return => self.op_return(ctx, &mut reader, mc),
+
+                MakeAttrs => self.op_make_attrs(ctx, &mut reader, mc),
+                MakeEmptyAttrs => self.op_make_empty_attrs(),
+                SelectStatic => self.op_select_static(ctx, &mut reader, mc),
+                SelectDynamic => self.op_select_dynamic(ctx, &mut reader, mc),
+                HasAttrPathStatic => self.op_has_attr_path_static(ctx, &mut reader, mc),
+                HasAttrPathDynamic => self.op_has_attr_path_dynamic(ctx, &mut reader, mc),
+                HasAttrStatic => self.op_has_attr_static(&mut reader, mc),
+                HasAttrDynamic => self.op_has_attr_dynamic(ctx, &mut reader, mc),
+                HasAttrResolve => self.op_has_attr_resolve(),
+                JumpIfSelectFailed => self.op_jump_if_select_failed(&mut reader),
+                JumpIfSelectSucceeded => self.op_jump_if_select_succeeded(&mut reader),
+
+                MakeList => self.op_make_list(ctx, &mut reader, mc),
+                MakeEmptyList => self.op_make_empty_list(),
+
+                OpAdd => self.op_add(ctx, &mut reader, mc),
+                OpSub => self.op_sub(&mut reader, mc),
+                OpMul => self.op_mul(&mut reader, mc),
+                OpDiv => self.op_div(&mut reader, mc),
+                OpEq => self.op_eq(ctx, &mut reader, mc),
+                OpNeq => self.op_neq(ctx, &mut reader, mc),
+                OpLt => self.op_lt(ctx, &mut reader, mc),
+                OpGt => self.op_gt(ctx, &mut reader, mc),
+                OpLeq => self.op_leq(ctx, &mut reader, mc),
+                OpGeq => self.op_geq(ctx, &mut reader, mc),
+                OpConcat => self.op_concat(&mut reader, mc),
+                OpUpdate => self.op_update(&mut reader, mc),
+
+                OpNeg => self.op_neg(&mut reader, mc),
+                OpNot => self.op_not(&mut reader, mc),
+
+                JumpIfFalse => self.op_jump_if_false(&mut reader, mc),
+                JumpIfTrue => self.op_jump_if_true(&mut reader, mc),
+                Jump => self.op_jump(&mut reader),
+
+                ConcatStrings => self.op_concat_strings(ctx, &mut reader, mc),
+                CoerceToString => self.op_coerce_to_string(&mut reader, mc),
+                ResolvePath => self.op_resolve_path(ctx, &mut reader, mc),
+
+                Assert => self.op_assert(ctx, &mut reader, mc),
+
+                LookupWith => self.op_lookup_with(ctx, &mut reader, mc),
+
+                LoadBuiltins => self.op_load_builtins(),
+                LoadBuiltin => self.op_load_builtin(&mut reader),
+
+                LoadReplBinding => self.op_load_repl_binding(&mut reader),
+                LoadScopedBinding => self.op_load_scoped_binding(ctx, &mut reader, mc),
+
+                Illegal => unreachable!(),
+            };
+
+            match result {
+                Step::Continue(()) | Step::Break(Break::Force) => {}
+                Step::Break(Break::Done) => {
+                    return Action::Done(self.result.take().expect("Break::Done without result"));
+                }
+                Step::Break(Break::LoadFile) => {
+                    return Action::LoadFile(
+                        self.pending_load
+                            .take()
+                            .expect("Break::LoadFile without pending_load"),
+                    );
+                }
+            }
+        }
+    }
+}

fix/Cargo.toml

@@ -0,0 +1,59 @@
+[package]
+name = "fix"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+mimalloc = "0.1"
+
+# REPL
+anyhow = "1.0"
+rustyline = "18.0"
+
+# CLI
+clap = { version = "4", features = ["derive"] }
+
+# Logging
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+
+# Error Reporting
+thiserror = "2"
+miette = { version = "7.4", features = ["fancy"] }
+
+# Data Structure
+hashbrown = { workspace = true }
+string-interner = { workspace = true }
+
+# Memory Management
+bumpalo = { workspace = true }
+
+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-ir = { path = "../fix-ir" }
+fix-vm = { path = "../fix-vm" }
+
+[dev-dependencies]
+criterion = { version = "0.8", features = ["html_reports"] }
+tempfile = "3.24"
+test-log = { version = "0.2", features = ["trace"] }
+
+[[bench]]
+name = "basic_ops"
+harness = false
+
+[[bench]]
+name = "builtins"
+harness = false
+
+[[bench]]
+name = "thunk_scope"
+harness = false

fix/benches/utils.rs

@@ -0,0 +1,15 @@
+#![allow(dead_code)]
+
+use fix::Evaluator;
+use fix_common::Value;
+use fix_error::{Result, Source};
+
+pub fn eval(expr: &str) -> Value {
+    Evaluator::new()
+        .eval(Source::new_eval(expr.into()).unwrap())
+        .unwrap()
+}
+
+pub fn eval_result(expr: &str) -> Result<Value> {
+    Evaluator::new().eval(Source::new_eval(expr.into()).unwrap())
+}

fix/src/error.rs

@@ -1,14 +1,9 @@
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
-use deno_core::error::JsError;
-use deno_error::JsErrorClass as _;
-use itertools::Itertools as _;
 use miette::{Diagnostic, NamedSource, SourceSpan};
 use thiserror::Error;
 
-use crate::runtime::RuntimeContext;
-
 pub type Result<T> = core::result::Result<T, Box<Error>>;
 
 #[derive(Clone, Debug)]
@@ -130,8 +125,6 @@ pub enum Error {
         #[label("error occurred here")]
         span: Option<SourceSpan>,
         message: String,
-        #[help]
-        js_backtrace: Option<String>,
         #[related]
         stack_trace: Vec<StackFrame>,
     },
@@ -168,12 +161,11 @@ impl Error {
         .into()
     }
 
-    pub fn eval_error(msg: String, backtrace: Option<String>) -> Box<Self> {
+    pub fn eval_error(msg: impl Into<String>) -> Box<Self> {
         Error::EvalError {
             src: None,
             span: None,
-            message: msg,
+            message: msg.into(),
-            js_backtrace: backtrace,
             stack_trace: Vec::new(),
         }
         .into()
@@ -229,127 +221,3 @@ pub struct StackFrame {
     #[source_code]
     pub src: NamedSource<Arc<str>>,
 }
-
-const MAX_STACK_FRAMES: usize = 20;
-const FRAMES_AT_START: usize = 15;
-const FRAMES_AT_END: usize = 5;
-
-pub(crate) fn parse_js_error(error: Box<JsError>, ctx: &impl RuntimeContext) -> Error {
-    let (span, src, frames) = if let Some(stack) = &error.stack {
-        let mut frames = parse_frames(stack, ctx);
-
-        if let Some(last_frame) = frames.pop() {
-            (
-                Some(text_range_to_source_span(last_frame.span)),
-                Some(last_frame.src.into()),
-                frames,
-            )
-        } else {
-            (None, None, frames)
-        }
-    } else {
-        (None, None, Vec::new())
-    };
-    let stack_trace = if std::env::var("NIX_JS_STACK_TRACE").is_ok() {
-        truncate_stack_trace(frames)
-    } else {
-        Vec::new()
-    };
-    let message = error.get_message().to_string();
-    let js_backtrace = error.stack.map(|stack| {
-        stack
-            .lines()
-            .filter(|line| !line.starts_with("NIX_STACK_FRAME:"))
-            .join("\n")
-    });
-
-    Error::EvalError {
-        src,
-        span,
-        message,
-        js_backtrace,
-        stack_trace,
-    }
-}
-
-struct NixStackFrame {
-    span: rnix::TextRange,
-    message: String,
-    src: Source,
-}
-
-impl From<NixStackFrame> for StackFrame {
-    fn from(NixStackFrame { span, message, src }: NixStackFrame) -> Self {
-        StackFrame {
-            span: text_range_to_source_span(span),
-            message,
-            src: src.into(),
-        }
-    }
-}
-
-fn parse_frames(stack: &str, ctx: &impl RuntimeContext) -> Vec<NixStackFrame> {
-    let mut frames = Vec::new();
-
-    for line in stack.lines() {
-        // Format: NIX_STACK_FRAME:span_id:message
-        let Some(rest) = line.strip_prefix("NIX_STACK_FRAME:") else {
-            continue;
-        };
-        let parts: Vec<&str> = rest.splitn(2, ':').collect();
-
-        if parts.is_empty() {
-            continue;
-        }
-
-        let span_id: usize = match parts[0].parse() {
-            Ok(id) => id,
-            Err(_) => continue,
-        };
-        let (source_id, span) = ctx.get_span(span_id);
-        let src = ctx.get_source(source_id);
-
-        let message = if parts.len() == 2 {
-            parts[1].to_string()
-        } else {
-            String::new()
-        };
-
-        frames.push(NixStackFrame { span, message, src });
-    }
-
-    frames.dedup_by(|a, b| a.span == b.span && a.message == b.message);
-
-    frames
-}
-
-fn truncate_stack_trace(frames: Vec<NixStackFrame>) -> Vec<StackFrame> {
-    let reversed: Vec<_> = frames.into_iter().rev().collect();
-    let total = reversed.len();
-
-    if total <= MAX_STACK_FRAMES {
-        return reversed.into_iter().map(Into::into).collect();
-    }
-
-    let omitted_count = total - FRAMES_AT_START - FRAMES_AT_END;
-
-    reversed
-        .into_iter()
-        .enumerate()
-        .filter_map(|(i, frame)| {
-            if i < FRAMES_AT_START {
-                Some(frame.into())
-            } else if i == FRAMES_AT_START {
-                Some(StackFrame {
-                    span: text_range_to_source_span(frame.span),
-                    message: format!("... ({} more frames omitted)", omitted_count),
-                    src: frame.src.into(),
-                })
-            } else if i >= total - FRAMES_AT_END {
-                Some(frame.into())
-            } else {
-                None
-            }
-        })
-        .collect()
-}

fix/src/fetcher.rs

@@ -5,8 +5,6 @@ use nix_compat::nixhash::HashAlgo;
 use nix_compat::nixhash::NixHash;
 use tracing::{debug, info, warn};
 
-use crate::runtime::OpStateExt;
-use crate::runtime::RuntimeContext;
 use crate::store::Store as _;
 
 mod archive;
@@ -20,7 +18,6 @@ pub use download::Downloader;
 pub use metadata_cache::MetadataCache;
 
 use crate::nar;
-use crate::runtime::NixRuntimeError;
 
 #[derive(ToV8)]
 pub struct FetchUrlResult {
@@ -306,11 +303,3 @@ fn normalize_hash(hash: &str) -> String {
     }
     hash.to_string()
 }
-
-pub fn register_ops<Ctx: RuntimeContext>() -> Vec<deno_core::OpDecl> {
-    vec![
-        op_fetch_url::<Ctx>(),
-        op_fetch_tarball::<Ctx>(),
-        op_fetch_git::<Ctx>(),
-    ]
-}

fix/src/fetcher/cache.rs

@@ -10,7 +10,7 @@ impl FetcherCache {
     pub fn new() -> Result<Self, std::io::Error> {
         let base_dir = dirs::cache_dir()
             .unwrap_or_else(|| PathBuf::from("/tmp"))
-            .join("nix-js")
+            .join("fix")
             .join("fetchers");
 
         fs::create_dir_all(&base_dir)?;

fix/src/lib.rs

@@ -0,0 +1,724 @@
+#![warn(clippy::unwrap_used)]
+#![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, Op};
+use fix_common::{StringId, Symbol};
+use fix_error::{Error, Result, Source};
+use fix_ir::downgrade::{Downgrade as _, DowngradeContext};
+use fix_ir::{
+    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 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 {
+    pub runtime: RuntimeState,
+    pub code: CodeState,
+}
+
+impl Default for Evaluator {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Evaluator {
+    pub fn new() -> Self {
+        let mut strings = DefaultStringInterner::new();
+        let 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(),
+                thunk_count: 0,
+                bytecode,
+                global_env,
+                current_scope_slot: None,
+            },
+        }
+    }
+
+    pub fn eval(&mut self, source: Source) -> Result<fix_common::Value> {
+        self.do_eval(source, None, ForceMode::AsIs)
+    }
+
+    pub fn eval_shallow(&mut self, source: Source) -> Result<fix_common::Value> {
+        self.do_eval(source, None, ForceMode::Shallow)
+    }
+
+    pub fn eval_deep(&mut self, source: Source) -> Result<fix_common::Value> {
+        self.do_eval(source, None, ForceMode::Deep)
+    }
+
+    pub fn eval_repl(
+        &mut self,
+        source: Source,
+        scope: &HashSet<StringId>,
+    ) -> Result<fix_common::Value> {
+        self.do_eval(source, Some(ExtraScope::Repl(scope)), ForceMode::Shallow)
+    }
+
+    fn do_eval<'ctx>(
+        &'ctx mut self,
+        source: Source,
+        extra_scope: Option<ExtraScope<'ctx>>,
+        force_mode: ForceMode,
+    ) -> Result<fix_common::Value> {
+        let ip = {
+            let mut compiler = CompilerCtx {
+                code: &mut self.code,
+                runtime: &mut self.runtime,
+            };
+            compiler.compile_bytecode(source, extra_scope)?
+        };
+        Vm::run(self, ip, force_mode)
+    }
+
+    pub fn add_binding(
+        &mut self,
+        _ident: &str,
+        _expr: &str,
+        _scope: &mut HashSet<StringId>,
+    ) -> Result<fix_common::Value> {
+        todo!("add_binding")
+    }
+
+    pub fn compile_bytecode(&mut self, source: Source) -> Result<InstructionPtr> {
+        let mut compiler = CompilerCtx {
+            code: &mut self.code,
+            runtime: &mut self.runtime,
+        };
+        compiler.compile_bytecode(source, None)
+    }
+
+    pub fn disassemble_colored(&self, ip: InstructionPtr) -> String {
+        Disassembler::new(ip, self).disassemble_colored()
+    }
+}
+
+impl VmRuntimeCtx for RuntimeState {
+    fn intern_string(&mut self, s: impl AsRef<str>) -> StringId {
+        StringId(self.strings.get_or_intern(s))
+    }
+    fn resolve_string(&self, id: StringId) -> &str {
+        #[allow(clippy::unwrap_used)]
+        self.strings.resolve(id.0).unwrap()
+    }
+    fn get_const(&self, id: u32) -> StaticValue {
+        #[allow(clippy::unwrap_used)]
+        self.constants.get(id).unwrap()
+    }
+    fn add_const(&mut self, val: StaticValue) -> u32 {
+        self.constants.insert(val)
+    }
+}
+
+impl VmCode for CodeState {
+    fn bytecode(&self) -> &[u8] {
+        &self.bytecode
+    }
+    fn compile_with_scope(
+        &mut self,
+        source: Source,
+        extra_scope: Option<fix_abstract_vm::ExtraScope>,
+        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.code.sources.push(source.clone());
+
+        let root = rnix::Root::parse(&source.src);
+        handle_parse_error(root.errors(), source.clone()).map_or(Ok(()), Err)?;
+
+        tracing::debug!("Downgrading Nix expression");
+        let expr = root
+            .tree()
+            .expr()
+            .ok_or_else(|| Error::parse_error("unexpected EOF".into()))?;
+        let bump = Bump::new();
+        GhostToken::new(|token| {
+            let downgrade_ctx = DowngradeCtx::new(
+                &bump,
+                token,
+                self.runtime,
+                &self.code.global_env,
+                extra_scope.map(Into::into),
+                &mut self.code.thunk_count,
+                source,
+            );
+            let ir = downgrade_ctx.downgrade_toplevel(expr)?;
+            let ir = unsafe { std::mem::transmute::<RawIrRef<'_>, RawIrRef<'static>>(ir) };
+            Ok(OwnedIr { _bump: bump, ir })
+        })
+    }
+}
+
+impl<'a, R: VmRuntimeCtx> BytecodeContext for CompilerCtx<'a, R> {
+    fn intern_string(&mut self, s: &str) -> StringId {
+        self.runtime.intern_string(s)
+    }
+
+    fn register_span(&mut self, range: rnix::TextRange) -> u32 {
+        let id = self.code.spans.len();
+        let source_id = self
+            .code
+            .sources
+            .len()
+            .checked_sub(1)
+            .expect("current_source not set");
+        self.code.spans.push((source_id, range));
+        id as u32
+    }
+
+    fn get_code(&self) -> &[u8] {
+        &self.code.bytecode
+    }
+
+    fn get_code_mut(&mut self) -> &mut Vec<u8> {
+        &mut self.code.bytecode
+    }
+
+    fn add_constant(&mut self, val: 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)]
+pub struct Constants {
+    data: Vec<StaticValue>,
+    dedup: HashMap<u64, u32>,
+}
+
+impl Constants {
+    fn insert(&mut self, val: StaticValue) -> u32 {
+        let bits = val.to_bits();
+        *self.dedup.entry(bits).or_insert_with(|| {
+            let idx = self.data.len() as u32;
+            self.data.push(val);
+            idx
+        })
+    }
+
+    fn get(&self, id: u32) -> Option<StaticValue> {
+        self.data.get(id as usize).copied()
+    }
+}
+
+fn parse_error_span(error: &rnix::ParseError) -> Option<rnix::TextRange> {
+    use rnix::ParseError::*;
+    match error {
+        Unexpected(range)
+        | UnexpectedExtra(range)
+        | UnexpectedWanted(_, range, _)
+        | UnexpectedDoubleBind(range)
+        | DuplicatedArgs(range, _) => Some(*range),
+        _ => None,
+    }
+}
+
+fn handle_parse_error<'a>(
+    errors: impl IntoIterator<Item = &'a rnix::ParseError>,
+    source: Source,
+) -> Option<Box<Error>> {
+    for err in errors {
+        if let Some(span) = parse_error_span(err) {
+            return Some(
+                Error::parse_error(err.to_string())
+                    .with_source(source)
+                    .with_span(span),
+            );
+        }
+    }
+    None
+}
+
+struct DowngradeCtx<'ctx, 'id, 'ir, R: VmRuntimeCtx> {
+    bump: &'ir Bump,
+    token: GhostToken<'id>,
+    runtime: &'ctx mut R,
+    source: Source,
+    scopes: Vec<Scope<'ctx, 'id, 'ir>>,
+    with_stack: Vec<GhostRoMaybeThunkRef<'id, 'ir>>,
+    arg_count: u32,
+    thunk_count: &'ctx mut usize,
+    thunk_scopes: Vec<ThunkScope<'id, 'ir>>,
+}
+
+impl<'ctx, 'id, 'ir, R: VmRuntimeCtx> DowngradeCtx<'ctx, 'id, 'ir, R> {
+    fn new(
+        bump: &'ir Bump,
+        token: GhostToken<'id>,
+        runtime: &'ctx mut R,
+        global: &'ctx HashMap<StringId, MaybeThunk>,
+        extra_scope: Option<Scope<'ctx, 'id, 'ir>>,
+        thunk_count: &'ctx mut usize,
+        source: Source,
+    ) -> Self {
+        Self {
+            bump,
+            token,
+            runtime,
+            source,
+            scopes: std::iter::once(Scope::Global(global))
+                .chain(extra_scope)
+                .collect(),
+            thunk_count,
+            arg_count: 0,
+            with_stack: Vec::new(),
+            thunk_scopes: vec![ThunkScope::new_in(bump)],
+        }
+    }
+}
+
+impl<'ctx: 'ir, 'id, 'ir, R: VmRuntimeCtx> DowngradeContext<'id, 'ir>
+    for DowngradeCtx<'ctx, 'id, 'ir, R>
+{
+    fn new_expr(&self, expr: Ir<'ir, GhostRoRef<'id, 'ir>>) -> GhostRoIrRef<'id, 'ir> {
+        self.bump.alloc(GhostCell::new(expr).into())
+    }
+
+    fn maybe_thunk(&mut self, ir: GhostRoIrRef<'id, 'ir>) -> GhostRoMaybeThunkRef<'id, 'ir> {
+        use MaybeThunk::*;
+        let expr = (|| {
+            let expr = match *ir.borrow(&self.token) {
+                Ir::Builtin(x) => Builtin(x),
+                Ir::Int(x) => Int(x),
+                Ir::Float(x) => Float(x),
+                Ir::Bool(x) => Bool(x),
+                Ir::Str(x) => Str(x),
+                Ir::Arg { layer } => Arg { layer },
+                Ir::Builtins => Builtins,
+                Ir::Null => Null,
+                Ir::MaybeThunk(thunk) => return Some(thunk),
+                _ => return None,
+            };
+            Some(self.bump.alloc(GhostCell::new(expr).into()))
+        })();
+        if let Some(thunk) = expr {
+            return thunk;
+        }
+        let id = ThunkId(*self.thunk_count);
+        *self.thunk_count = self.thunk_count.checked_add(1).expect("thunk id overflow");
+        self.thunk_scopes
+            .last_mut()
+            .expect("no active cache scope")
+            .add_binding(id, ir);
+        self.bump.alloc(GhostCell::new(Thunk(id)).into())
+    }
+
+    fn intern_string(&mut self, sym: impl AsRef<str>) -> StringId {
+        self.runtime.intern_string(sym)
+    }
+
+    fn resolve_sym(&self, id: StringId) -> Symbol<'_> {
+        self.runtime.resolve_string(id).into()
+    }
+
+    fn lookup(
+        &mut self,
+        sym: StringId,
+        span: rnix::TextRange,
+    ) -> Result<GhostRoMaybeThunkRef<'id, 'ir>> {
+        for scope in self.scopes.iter().rev() {
+            match scope {
+                &Scope::Global(global_scope) => {
+                    if let Some(expr) = global_scope.get(&sym) {
+                        return Ok(expr.into());
+                    }
+                }
+                &Scope::Repl(repl_bindings) => {
+                    if repl_bindings.contains(&sym) {
+                        return Ok(self
+                            .bump
+                            .alloc(GhostCell::new(MaybeThunk::ReplBinding(sym)).into()));
+                    }
+                }
+                Scope::ScopedImport { keys, .. } => {
+                    if keys.contains(&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(expr.into());
+                    }
+                }
+                &Scope::Param {
+                    sym: param_sym,
+                    abs_layer,
+                } => {
+                    if param_sym == sym {
+                        let layers: u8 =
+                            self.thunk_scopes.len().try_into().expect("scope too deep!");
+                        let layer = layers - abs_layer;
+                        return Ok(self
+                            .bump
+                            .alloc(GhostCell::new(MaybeThunk::Arg { layer }).into()));
+                    }
+                }
+            }
+        }
+
+        if !self.with_stack.is_empty() {
+            let id = ThunkId(*self.thunk_count);
+            *self.thunk_count = self.thunk_count.checked_add(1).expect("thunk id overflow");
+            let mut namespaces =
+                bumpalo::collections::Vec::with_capacity_in(self.with_stack.len(), self.bump);
+            namespaces.extend(self.with_stack.iter().rev().copied());
+            let body = self
+                .bump
+                .alloc(GhostCell::new(Ir::WithLookup { sym, namespaces }).into());
+            self.thunk_scopes
+                .last_mut()
+                .expect("no active thunk scope")
+                .add_binding(id, body);
+            Ok(self
+                .bump
+                .alloc(GhostCell::new(MaybeThunk::Thunk(id)).into()))
+        } else {
+            Err(Error::downgrade_error(
+                format!("'{}' not found", self.resolve_sym(sym)),
+                self.get_current_source(),
+                span,
+            ))
+        }
+    }
+
+    fn get_current_source(&self) -> Source {
+        self.source.clone()
+    }
+
+    fn with_let_scope<F, Ret>(&mut self, keys: &[StringId], f: F) -> Result<Ret>
+    where
+        F: FnOnce(
+            &mut Self,
+        ) -> Result<(
+            bumpalo::collections::Vec<'ir, GhostRoMaybeThunkRef<'id, 'ir>>,
+            Ret,
+        )>,
+    {
+        let base = *self.thunk_count;
+        *self.thunk_count = self
+            .thunk_count
+            .checked_add(keys.len())
+            .expect("thunk id overflow");
+        let handles = (base..base + keys.len())
+            .map(|id| {
+                &*self
+                    .bump
+                    .alloc(GhostCell::new(MaybeThunk::Thunk(ThunkId(id))))
+            })
+            .collect::<Vec<_>>();
+        let scope = keys.iter().copied().zip(handles.iter().copied()).collect();
+        self.scopes.push(Scope::Let(scope));
+        let (vals, ret) = { f(self)? };
+        self.scopes.pop();
+        assert_eq!(keys.len(), vals.len());
+        let scope = self.thunk_scopes.last_mut().expect("no active thunk scope");
+        for (i, (val, handle)) in vals.into_iter().zip(handles).enumerate() {
+            let thunk = *val.borrow(&self.token);
+            *handle.borrow_mut(&mut self.token) = thunk;
+            let id = ThunkId(base + i);
+            let ir_ref = self
+                .bump
+                .alloc(GhostCell::new(Ir::MaybeThunk(handle.into())).into());
+            scope.add_binding(id, ir_ref);
+        }
+        Ok(ret)
+    }
+
+    fn with_param_scope<F, Ret>(&mut self, sym: StringId, f: F) -> Ret
+    where
+        F: FnOnce(&mut Self) -> Ret,
+    {
+        self.scopes.push(Scope::Param {
+            sym,
+            abs_layer: self.thunk_scopes.len().try_into().expect("scope too deep!"),
+        });
+        let mut guard = ScopeGuard { ctx: self };
+        f(guard.as_ctx())
+    }
+
+    fn with_with_scope<F, Ret>(&mut self, namespace: GhostRoMaybeThunkRef<'id, 'ir>, f: F) -> Ret
+    where
+        F: FnOnce(&mut Self) -> Ret,
+    {
+        self.with_stack.push(namespace);
+        let ret = f(self);
+        self.with_stack.pop();
+        ret
+    }
+
+    fn with_thunk_scope<F, Ret>(
+        &mut self,
+        f: F,
+    ) -> (
+        Ret,
+        bumpalo::collections::Vec<'ir, (ThunkId, GhostRoIrRef<'id, 'ir>)>,
+    )
+    where
+        F: FnOnce(&mut Self) -> Ret,
+    {
+        if self.thunk_scopes.len() == u8::MAX as usize {
+            panic!("scope too deep!");
+        }
+        self.thunk_scopes.push(ThunkScope::new_in(self.bump));
+        let ret = f(self);
+        (
+            ret,
+            self.thunk_scopes
+                .pop()
+                .expect("no thunk scope left???")
+                .bindings,
+        )
+    }
+
+    fn bump(&self) -> &'ir bumpalo::Bump {
+        self.bump
+    }
+}
+
+impl<'id, 'ir, 'ctx: 'ir, R: VmRuntimeCtx> DowngradeCtx<'ctx, 'id, 'ir, R> {
+    fn downgrade_toplevel(mut self, root: rnix::ast::Expr) -> Result<RawIrRef<'ir>> {
+        let body = root.downgrade(&mut self)?;
+        let thunks = self
+            .thunk_scopes
+            .pop()
+            .expect("no thunk scope left???")
+            .bindings;
+        Ok(Ir::freeze(
+            self.new_expr(Ir::TopLevel { body, thunks }),
+            self.token,
+        ))
+    }
+}
+
+struct ThunkScope<'id, 'ir> {
+    bindings: bumpalo::collections::Vec<'ir, (ThunkId, GhostRoIrRef<'id, 'ir>)>,
+}
+
+impl<'id, 'ir> ThunkScope<'id, 'ir> {
+    fn new_in(bump: &'ir Bump) -> Self {
+        Self {
+            bindings: bumpalo::collections::Vec::new_in(bump),
+        }
+    }
+
+    fn add_binding(&mut self, id: ThunkId, ir: GhostRoIrRef<'id, 'ir>) {
+        self.bindings.push((id, ir));
+    }
+
+    fn extend_bindings(
+        &mut self,
+        iter: impl IntoIterator<Item = (ThunkId, GhostRoIrRef<'id, 'ir>)>,
+    ) {
+        self.bindings.extend(iter);
+    }
+}
+
+enum Scope<'ctx, 'id, 'ir> {
+    Global(&'ctx HashMap<StringId, MaybeThunk>),
+    Repl(&'ctx HashSet<StringId>),
+    ScopedImport {
+        keys: HashSet<StringId>,
+        slot_id: u32,
+    },
+    Let(HashMap<StringId, GhostMaybeThunkRef<'id, 'ir>>),
+    Param {
+        sym: StringId,
+        abs_layer: u8,
+    },
+}
+
+pub enum ExtraScope<'ctx> {
+    Repl(&'ctx HashSet<StringId>),
+    ScopedImport {
+        keys: HashSet<StringId>,
+        slot_id: u32,
+    },
+}
+
+impl<'ctx> From<ExtraScope<'ctx>> for Scope<'ctx, '_, '_> {
+    fn from(value: ExtraScope<'ctx>) -> Self {
+        use ExtraScope::*;
+        match value {
+            ScopedImport { keys, slot_id } => Scope::ScopedImport { keys, slot_id },
+            Repl(scope) => Scope::Repl(scope),
+        }
+    }
+}
+
+struct ScopeGuard<'a, 'ctx, 'id, 'ir, R: VmRuntimeCtx> {
+    ctx: &'a mut DowngradeCtx<'ctx, 'id, 'ir, R>,
+}
+
+impl<'a, 'ctx, 'id, 'ir, R: VmRuntimeCtx> Drop for ScopeGuard<'a, 'ctx, 'id, 'ir, R> {
+    fn drop(&mut self) {
+        self.ctx.scopes.pop();
+    }
+}
+
+impl<'a, 'ctx, 'id, 'ir, R: VmRuntimeCtx> ScopeGuard<'a, 'ctx, 'id, 'ir, R> {
+    fn as_ctx(&mut self) -> &mut DowngradeCtx<'ctx, 'id, 'ir, R> {
+        self.ctx
+    }
+}
+
+struct OwnedIr {
+    _bump: Bump,
+    ir: RawIrRef<'static>,
+}
+
+impl OwnedIr {
+    /// # Safety
+    /// `ir` must be an allocation backed by `bump`. The reference's
+    /// 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<'ir>(&'ir self) -> RawIrRef<'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
+        // (`Ref::Ref<T>`), which prevents the compiler from inferring
+        // covariance automatically. The bump arena that backs the IR is
+        // owned by `self._bump`, so the data is live for at least `'ir`.
+        unsafe { std::mem::transmute::<RawIrRef<'static>, RawIrRef<'ir>>(self.ir) }
+    }
+}
+
+impl DisassemblerContext for Evaluator {
+    fn get_code(&self) -> &[u8] {
+        &self.code.bytecode
+    }
+
+    #[allow(clippy::unwrap_used)]
+    fn resolve_string(&self, id: u32) -> &str {
+        let id = string_interner::symbol::SymbolU32::try_from_usize(id as usize).unwrap();
+        self.runtime.strings.resolve(id).unwrap()
+    }
+}

fix/src/logging.rs

@@ -1,7 +1,9 @@
 use std::env;
 use std::io::IsTerminal;
 
-use tracing_subscriber::{EnvFilter, Layer, fmt, layer::SubscriberExt, util::SubscriberInitExt};
+use tracing_subscriber::layer::SubscriberExt;
+use tracing_subscriber::util::SubscriberInitExt;
+use tracing_subscriber::{EnvFilter, Layer, fmt};
 
 pub fn init_logging() {
     let is_terminal = std::io::stderr().is_terminal();

fix/src/main.rs

@@ -3,23 +3,15 @@ use std::process::exit;
 
 use anyhow::Result;
 use clap::{Args, Parser, Subcommand};
+use fix::Evaluator;
+use fix_error::Source;
 use hashbrown::HashSet;
-use nix_js::context::Context;
-use nix_js::error::Source;
 use rustyline::DefaultEditor;
 use rustyline::error::ReadlineError;
 
 #[derive(Parser)]
-#[command(name = "nix-js", about = "Nix expression evaluator")]
+#[command(name = "fix", about = "Nix expression evaluator")]
 struct Cli {
-    #[cfg(feature = "inspector")]
-    #[arg(long, value_name = "HOST:PORT", num_args = 0..=1, default_missing_value = "127.0.0.1:9229")]
-    inspect: Option<String>,
-
-    #[cfg(feature = "inspector")]
-    #[arg(long, value_name = "HOST:PORT", num_args = 0..=1, default_missing_value = "127.0.0.1:9229")]
-    inspect_brk: Option<String>,
-
     #[command(subcommand)]
     command: Command,
 }
@@ -48,28 +40,7 @@ struct ExprSource {
     file: Option<PathBuf>,
 }
 
-fn create_context(#[cfg(feature = "inspector")] cli: &Cli) -> Result<Context> {
+fn run_compile(eval: &mut Evaluator, src: ExprSource, silent: bool) -> Result<()> {
-    #[cfg(feature = "inspector")]
-    {
-        let (addr_str, wait) = if let Some(ref addr) = cli.inspect_brk {
-            (Some(addr.as_str()), true)
-        } else if let Some(ref addr) = cli.inspect {
-            (Some(addr.as_str()), false)
-        } else {
-            (None, false)
-        };
-
-        if let Some(addr_str) = addr_str {
-            let addr: std::net::SocketAddr = addr_str
-                .parse()
-                .map_err(|e| anyhow::anyhow!("invalid inspector address '{}': {}", addr_str, e))?;
-            return Ok(Context::new_with_inspector(addr, wait)?);
-        }
-    }
-    Ok(Context::new()?)
-}
-
-fn run_compile(context: &mut Context, src: ExprSource, silent: bool) -> Result<()> {
     let src = if let Some(expr) = src.expr {
         Source::new_eval(expr)?
     } else if let Some(file) = src.file {
@@ -77,10 +48,10 @@ fn run_compile(context: &mut Context, src: ExprSource, silent: bool) -> Result<(
     } else {
         unreachable!()
     };
-    match context.compile_bytecode(src) {
+    match eval.compile_bytecode(src) {
-        Ok(compiled) => {
+        Ok(ip) => {
             if !silent {
-                println!("{}", context.disassemble_colored(&compiled));
+                println!("{}", eval.disassemble_colored(ip));
             }
         }
         Err(err) => {
@@ -88,12 +59,10 @@ fn run_compile(context: &mut Context, src: ExprSource, silent: bool) -> Result<(
             exit(1);
         }
     };
-    #[cfg(feature = "inspector")]
-    context.wait_for_inspector_disconnect();
     Ok(())
 }
 
-fn run_eval(context: &mut Context, src: ExprSource) -> Result<()> {
+fn run_eval(eval: &mut Evaluator, src: ExprSource) -> Result<()> {
     let src = if let Some(expr) = src.expr {
         Source::new_eval(expr)?
     } else if let Some(file) = src.file {
@@ -101,7 +70,7 @@ fn run_eval(context: &mut Context, src: ExprSource) -> Result<()> {
     } else {
         unreachable!()
     };
-    match context.eval_deep(src) {
+    match eval.eval_deep(src) {
         Ok(value) => {
             println!("{}", value.display_compat());
         }
@@ -110,17 +79,15 @@ fn run_eval(context: &mut Context, src: ExprSource) -> Result<()> {
             exit(1);
         }
     };
-    #[cfg(feature = "inspector")]
-    context.wait_for_inspector_disconnect();
     Ok(())
 }
 
-fn run_repl(context: &mut Context) -> Result<()> {
+fn run_repl(eval: &mut Evaluator) -> Result<()> {
     let mut rl = DefaultEditor::new()?;
     let mut scope = HashSet::new();
     const RE: ere::Regex<3> = ere::compile_regex!("^[ \t]*([a-zA-Z_][a-zA-Z0-9_'-]*)[ \t]*(.*)$");
     loop {
-        let readline = rl.readline("nix-js-repl> ");
+        let readline = rl.readline("fix-repl> ");
         match readline {
             Ok(line) => {
                 if line.trim().is_empty() {
@@ -134,20 +101,20 @@ fn run_repl(context: &mut Context) -> Result<()> {
                             eprintln!("Error: missing expression after '='");
                             continue;
                         }
-                        match context.add_binding(ident, expr, &mut scope) {
+                        match eval.add_binding(ident, expr, &mut scope) {
                             Ok(value) => println!("{} = {}", ident, value),
                             Err(err) => eprintln!("{:?}", miette::Report::new(*err)),
                         }
                     } else {
                         let src = Source::new_repl(line)?;
-                        match context.eval_repl(src, &scope) {
+                        match eval.eval_repl(src, &scope) {
                             Ok(value) => println!("{value}"),
                             Err(err) => eprintln!("{:?}", miette::Report::new(*err)),
                         }
                     }
                 } else {
                     let src = Source::new_repl(line)?;
-                    match context.eval_shallow(src) {
+                    match eval.eval_repl(src, &scope) {
                         Ok(value) => println!("{value}"),
                         Err(err) => eprintln!("{:?}", miette::Report::new(*err)),
                     }
@@ -170,18 +137,15 @@ fn run_repl(context: &mut Context) -> Result<()> {
 }
 
 fn main() -> Result<()> {
-    nix_js::logging::init_logging();
+    fix::logging::init_logging();
 
     let cli = Cli::parse();
 
-    let mut context = create_context(
+    let mut eval = Evaluator::new();
-        #[cfg(feature = "inspector")]
-        &cli,
-    )?;
 
     match cli.command {
-        Command::Compile { source, silent } => run_compile(&mut context, source, silent),
+        Command::Compile { source, silent } => run_compile(&mut eval, source, silent),
-        Command::Eval { source } => run_eval(&mut context, source),
+        Command::Eval { source } => run_eval(&mut eval, source),
-        Command::Repl => run_repl(&mut context),
+        Command::Repl => run_repl(&mut eval),
     }
 }

fix/src/nar.rs

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

fix/src/store.rs

@@ -7,7 +7,6 @@ mod validation;
 
 pub use config::StoreConfig;
 pub use daemon::DaemonStore;
-pub use validation::validate_store_path;
 
 pub trait Store: Send + Sync {
     fn get_store_dir(&self) -> &str;

fix/src/store/daemon.rs

@@ -69,13 +69,10 @@ impl Store for DaemonStore {
     fn ensure_path(&self, path: &str) -> Result<()> {
         self.block_on(async {
             self.connection.ensure_path(path).await.map_err(|e| {
-                Error::eval_error(
+                Error::eval_error(format!(
-                    format!(
                     "builtins.storePath: path '{}' is not valid in nix store: {}",
                     path, e
-                    ),
+                ))
-                    None,
-                )
             })
         })
     }

fix/src/store/validation.rs

@@ -2,75 +2,72 @@ use crate::error::{Error, Result};
 
 pub fn validate_store_path(store_dir: &str, path: &str) -> Result<()> {
     if !path.starts_with(store_dir) {
-        return Err(Error::eval_error(
+        return Err(Error::eval_error(format!(
-            format!("path '{}' is not in the Nix store", path),
+            "path '{}' is not in the Nix store",
-            None,
+            path
-        ));
+        )));
     }
 
     let relative = path
         .strip_prefix(store_dir)
         .and_then(|s| s.strip_prefix('/'))
-        .ok_or_else(|| Error::eval_error(format!("invalid store path format: {}", path), None))?;
+        .ok_or_else(|| Error::eval_error(format!("invalid store path format: {}", path)))?;
 
     if relative.is_empty() {
-        return Err(Error::eval_error(
+        return Err(Error::eval_error(format!(
-            format!("store path cannot be store directory itself: {}", path),
+            "store path cannot be store directory itself: {}",
-            None,
+            path
-        ));
+        )));
     }
 
     let parts: Vec<&str> = relative.splitn(2, '-').collect();
     if parts.len() != 2 {
-        return Err(Error::eval_error(
+        return Err(Error::eval_error(format!(
-            format!("invalid store path format (missing name): {}", path),
+            "invalid store path format (missing name): {}",
-            None,
+            path
-        ));
+        )));
     }
 
     let hash = parts[0];
     let name = parts[1];
 
     if hash.len() != 32 {
-        return Err(Error::eval_error(
+        return Err(Error::eval_error(format!(
-            format!(
             "invalid store path hash length (expected 32, got {}): {}",
             hash.len(),
             hash
-            ),
+        )));
-            None,
-        ));
     }
 
     for ch in hash.chars() {
         if !matches!(ch, '0'..='9' | 'a'..='d' | 'f'..='n' | 'p'..='s' | 'v'..='z') {
-            return Err(Error::eval_error(
+            return Err(Error::eval_error(format!(
-                format!("invalid character '{}' in store path hash: {}", ch, hash),
+                "invalid character '{}' in store path hash: {}",
-                None,
+                ch, hash
-            ));
+            )));
         }
     }
 
     if name.is_empty() {
-        return Err(Error::eval_error(
+        return Err(Error::eval_error(format!(
-            format!("store path has empty name: {}", path),
+            "store path has empty name: {}",
-            None,
+            path
-        ));
+        )));
     }
 
     if name.starts_with('.') {
-        return Err(Error::eval_error(
+        return Err(Error::eval_error(format!(
-            format!("store path name cannot start with '.': {}", name),
+            "store path name cannot start with '.': {}",
-            None,
+            name
-        ));
+        )));
     }
 
     for ch in name.chars() {
         if !matches!(ch, '0'..='9' | 'a'..='z' | 'A'..='Z' | '+' | '-' | '.' | '_' | '?' | '=') {
-            return Err(Error::eval_error(
+            return Err(Error::eval_error(format!(
-                format!("invalid character '{}' in store path name: {}", ch, name),
+                "invalid character '{}' in store path name: {}",
-                None,
+                ch, name
-            ));
+            )));
         }
     }
 

fix/tests/tests/derivation.rs

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

fix/tests/tests/io_operations.rs

@@ -1,6 +1,6 @@
-use nix_js::context::Context;
+use fix::Evaluator;
-use nix_js::error::Source;
+use fix_common::Value;
-use nix_js::value::Value;
+use fix_error::Source;
 
 use crate::utils::{eval, eval_result};
 
@@ -97,7 +97,7 @@ fn import_with_complex_dependency_graph() {
 
 #[test_log::test]
 fn path_with_file() {
-    let mut ctx = Context::new().unwrap();
+    let mut ctx = Evaluator::new();
     let temp_dir = tempfile::tempdir().unwrap();
     let test_file = temp_dir.path().join("test.txt");
     std::fs::write(&test_file, "Hello, World!").unwrap();
@@ -107,7 +107,7 @@ fn path_with_file() {
 
     // Should return a store path string
     if let Value::String(store_path) = result {
-        assert!(store_path.starts_with(ctx.get_store_dir()));
+        assert!(store_path.starts_with("/nix/store"));
         assert!(store_path.contains("test.txt"));
     } else {
         panic!("Expected string, got {:?}", result);
@@ -136,7 +136,7 @@ fn path_with_custom_name() {
 
 #[test_log::test]
 fn path_with_directory_recursive() {
-    let mut ctx = Context::new().unwrap();
+    let mut ctx = Evaluator::new();
     let temp_dir = tempfile::tempdir().unwrap();
     let test_dir = temp_dir.path().join("mydir");
     std::fs::create_dir_all(&test_dir).unwrap();
@@ -150,7 +150,7 @@ fn path_with_directory_recursive() {
     let result = ctx.eval(Source::new_eval(expr).unwrap()).unwrap();
 
     if let Value::String(store_path) = result {
-        assert!(store_path.starts_with(ctx.get_store_dir()));
+        assert!(store_path.starts_with("/nix/store"));
         assert!(store_path.contains("mydir"));
     } else {
         panic!("Expected string, got {:?}", result);
@@ -159,7 +159,7 @@ fn path_with_directory_recursive() {
 
 #[test_log::test]
 fn path_flat_with_file() {
-    let mut ctx = Context::new().unwrap();
+    let mut ctx = Evaluator::new();
     let temp_dir = tempfile::tempdir().unwrap();
     let test_file = temp_dir.path().join("flat.txt");
     std::fs::write(&test_file, "Flat content").unwrap();
@@ -171,7 +171,7 @@ fn path_flat_with_file() {
     let result = ctx.eval(Source::new_eval(expr).unwrap()).unwrap();
 
     if let Value::String(store_path) = result {
-        assert!(store_path.starts_with(ctx.get_store_dir()));
+        assert!(store_path.starts_with("/nix/store"));
     } else {
         panic!("Expected string, got {:?}", result);
     }
@@ -366,3 +366,193 @@ fn read_dir_on_file_fails() {
     let err_msg = result.unwrap_err().to_string();
     assert!(err_msg.contains("not a directory"));
 }
+
+#[test_log::test]
+fn to_file_simple() {
+    let result =
+        eval_result(r#"builtins.toFile "hello.txt" "Hello, World!""#).expect("Failed to evaluate");
+
+    match result {
+        Value::String(path) => {
+            assert!(path.contains("-hello.txt"));
+            assert!(std::path::Path::new(&path).exists());
+
+            let contents = std::fs::read_to_string(&path).expect("Failed to read file");
+            assert_eq!(contents, "Hello, World!");
+        }
+        _ => panic!("Expected string, got {:?}", result),
+    }
+}
+
+#[test_log::test]
+fn to_file_with_references() {
+    let result = eval_result(
+        r#"
+            let
+              dep = builtins.toFile "dep.txt" "dependency";
+            in
+              builtins.toFile "main.txt" "Reference: ${dep}"
+        "#,
+    )
+    .expect("Failed to evaluate");
+
+    match result {
+        Value::String(path) => {
+            assert!(path.contains("-main.txt"));
+            let contents = std::fs::read_to_string(&path).expect("Failed to read file");
+            assert!(contents.contains("Reference: "));
+            assert!(contents.contains("-dep.txt"));
+        }
+        _ => panic!("Expected string"),
+    }
+}
+
+#[test_log::test]
+fn to_file_invalid_name_with_slash() {
+    let result = eval_result(r#"builtins.toFile "foo/bar.txt" "content""#);
+
+    assert!(result.is_err());
+    assert!(
+        result
+            .unwrap_err()
+            .to_string()
+            .contains("name cannot contain '/'")
+    );
+}
+
+#[test_log::test]
+fn to_file_invalid_name_dot() {
+    let result = eval_result(r#"builtins.toFile "." "content""#);
+
+    assert!(result.is_err());
+    assert!(result.unwrap_err().to_string().contains("invalid name"));
+}
+
+#[test_log::test]
+fn to_file_invalid_name_dotdot() {
+    let result = eval_result(r#"builtins.toFile ".." "content""#);
+
+    assert!(result.is_err());
+    assert!(result.unwrap_err().to_string().contains("invalid name"));
+}
+
+#[test_log::test]
+fn store_path_validation_not_in_store() {
+    let result = eval_result(r#"builtins.storePath "/tmp/foo""#);
+
+    assert!(result.is_err());
+    assert!(
+        result
+            .unwrap_err()
+            .to_string()
+            .contains("not in the Nix store")
+    );
+}
+
+#[test_log::test]
+fn store_path_validation_malformed_hash() {
+    let dummy_file_result = eval_result(r#"builtins.toFile "dummy.txt" "content""#)
+        .expect("Failed to create dummy file");
+
+    let dummy_path = match dummy_file_result {
+        Value::String(ref p) => p.clone(),
+        _ => panic!("Expected string"),
+    };
+
+    let store_dir = std::path::Path::new(&dummy_path)
+        .parent()
+        .expect("Failed to get parent dir")
+        .to_str()
+        .expect("Failed to convert to string");
+
+    let test_path = format!("{}/invalid-hash-hello", store_dir);
+    let result = eval_result(&format!(r#"builtins.storePath "{}""#, test_path));
+
+    assert!(result.is_err());
+    let err_str = result.unwrap_err().to_string();
+    assert!(
+        err_str.contains("invalid") || err_str.contains("hash"),
+        "Expected hash validation error, got: {}",
+        err_str
+    );
+}
+
+#[test_log::test]
+fn store_path_validation_missing_name() {
+    let dummy_file_result = eval_result(r#"builtins.toFile "dummy.txt" "content""#)
+        .expect("Failed to create dummy file");
+
+    let dummy_path = match dummy_file_result {
+        Value::String(ref p) => p.clone(),
+        _ => panic!("Expected string"),
+    };
+
+    let store_dir = std::path::Path::new(&dummy_path)
+        .parent()
+        .expect("Failed to get parent dir")
+        .to_str()
+        .expect("Failed to convert to string");
+
+    let test_path = format!("{}/abcd1234abcd1234abcd1234abcd1234", store_dir);
+    let result = eval_result(&format!(r#"builtins.storePath "{}""#, test_path));
+
+    assert!(result.is_err());
+    let err_str = result.unwrap_err().to_string();
+    assert!(
+        err_str.contains("missing name") || err_str.contains("format"),
+        "Expected missing name error, got: {}",
+        err_str
+    );
+}
+
+#[test_log::test]
+fn to_file_curried_application() {
+    let result = eval_result(
+        r#"
+            let
+              makeFile = builtins.toFile "test.txt";
+            in
+              makeFile "test content"
+        "#,
+    )
+    .expect("Failed to evaluate");
+
+    match result {
+        Value::String(path) => {
+            assert!(path.contains("-test.txt"));
+            let contents = std::fs::read_to_string(&path).expect("Failed to read file");
+            assert_eq!(contents, "test content");
+        }
+        _ => panic!("Expected string"),
+    }
+}
+
+#[test_log::test]
+fn to_file_number_conversion() {
+    let result = eval_result(r#"builtins.toFile "number.txt" (builtins.toString 42)"#)
+        .expect("Failed to evaluate");
+
+    match result {
+        Value::String(path) => {
+            let contents = std::fs::read_to_string(&path).expect("Failed to read file");
+            assert_eq!(contents, "42");
+        }
+        _ => panic!("Expected string"),
+    }
+}
+
+#[test_log::test]
+fn to_file_list_conversion() {
+    let result = eval_result(
+        r#"builtins.toFile "list.txt" (builtins.concatStringsSep "\n" ["line1" "line2" "line3"])"#,
+    )
+    .expect("Failed to evaluate");
+
+    match result {
+        Value::String(path) => {
+            let contents = std::fs::read_to_string(&path).expect("Failed to read file");
+            assert_eq!(contents, "line1\nline2\nline3");
+        }
+        _ => panic!("Expected string"),
+    }
+}

fix/tests/tests/lang.rs

@@ -0,0 +1,326 @@
+#![allow(non_snake_case)]
+
+use std::path::PathBuf;
+
+use fix::Evaluator;
+use fix_common::Value;
+use fix_error::{Source, SourceType};
+
+fn get_lang_dir() -> PathBuf {
+    PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("tests/tests/lang")
+}
+
+fn eval_file(name: &str) -> Result<(Value, Source), String> {
+    let lang_dir = get_lang_dir();
+    let nix_path = lang_dir.join(format!("{name}.nix"));
+
+    let mut ctx = Evaluator::new();
+    let content = std::fs::read_to_string(&nix_path).unwrap();
+    let source = Source {
+        ty: SourceType::File(nix_path.into()),
+        src: content.into(),
+    };
+    ctx.eval_deep(source.clone())
+        .map(|val| (val, source))
+        .map_err(|e| e.to_string())
+}
+
+fn read_expected(name: &str) -> String {
+    let lang_dir = get_lang_dir();
+    let exp_path = lang_dir.join(format!("{name}.exp"));
+    std::fs::read_to_string(exp_path)
+        .expect("expected file should exist")
+        .trim_end()
+        .to_string()
+}
+
+fn format_value(value: &Value) -> String {
+    value.display_compat().to_string()
+}
+
+macro_rules! eval_okay_test {
+    ($(#[$attr:meta])* $name:ident$(, $pre:expr)?) => {
+        $(#[$attr])*
+        #[test_log::test]
+        fn $name() {
+            $(($pre)();)?
+            let test_name = concat!("eval-okay-", stringify!($name))
+                .replace("_", "-")
+                .replace("r#", "");
+            let result = eval_file(&test_name);
+            match result {
+                Ok((value, source)) => {
+                    let actual = format_value(&value);
+                    let actual = actual.replace(
+                        source
+                            .get_dir()
+                            .parent()
+                            .unwrap()
+                            .to_string_lossy()
+                            .as_ref(),
+                        "/pwd",
+                    );
+                    let expected = read_expected(&test_name);
+                    assert_eq!(actual, expected, "Output mismatch for {}", test_name);
+                }
+                Err(e) => {
+                    panic!("Test {} failed to evaluate: {}", test_name, e);
+                }
+            }
+        }
+    };
+}
+
+macro_rules! eval_fail_test {
+    ($name:ident) => {
+        #[test_log::test]
+        fn $name() {
+            let test_name = concat!("eval-fail-", stringify!($name))
+                .replace("_", "-")
+                .replace("r#", "");
+            let result = eval_file(&test_name);
+            assert!(
+                result.is_err(),
+                "Test {} should have failed but succeeded with: {:?}",
+                test_name,
+                result
+            );
+        }
+    };
+}
+
+mod okay {
+    use super::*;
+
+    eval_okay_test!(any_all);
+    eval_okay_test!(arithmetic);
+    eval_okay_test!(attrnames);
+    eval_okay_test!(attrs);
+    eval_okay_test!(attrs2);
+    eval_okay_test!(attrs3);
+    eval_okay_test!(attrs4);
+    eval_okay_test!(attrs5);
+    eval_okay_test!(
+        #[ignore = "__overrides is not supported"]
+        attrs6
+    );
+    eval_okay_test!(
+        #[ignore = "requires --arg/--argstr CLI flags"]
+        autoargs
+    );
+    eval_okay_test!(backslash_newline_1);
+    eval_okay_test!(backslash_newline_2);
+    eval_okay_test!(baseNameOf);
+    eval_okay_test!(builtins);
+    eval_okay_test!(builtins_add);
+    eval_okay_test!(callable_attrs);
+    eval_okay_test!(catattrs);
+    eval_okay_test!(closure);
+    eval_okay_test!(comments);
+    eval_okay_test!(concat);
+    eval_okay_test!(concatmap);
+    eval_okay_test!(concatstringssep);
+    eval_okay_test!(context);
+    eval_okay_test!(context_introspection);
+    eval_okay_test!(convertHash);
+    eval_okay_test!(curpos);
+    eval_okay_test!(deepseq);
+    eval_okay_test!(delayed_with);
+    eval_okay_test!(delayed_with_inherit);
+    eval_okay_test!(deprecate_cursed_or);
+    eval_okay_test!(derivation_legacy);
+    eval_okay_test!(dynamic_attrs);
+    eval_okay_test!(dynamic_attrs_2);
+    eval_okay_test!(dynamic_attrs_bare);
+    eval_okay_test!(elem);
+    eval_okay_test!(empty_args);
+    eval_okay_test!(eq);
+    eval_okay_test!(eq_derivations);
+    eval_okay_test!(filter);
+    eval_okay_test!(
+        #[ignore = "not implemented: flakeRefToString"]
+        flake_ref_to_string
+    );
+    eval_okay_test!(flatten);
+    eval_okay_test!(float);
+    eval_okay_test!(floor_ceil);
+    eval_okay_test!(foldlStrict);
+    eval_okay_test!(foldlStrict_lazy_elements);
+    eval_okay_test!(foldlStrict_lazy_initial_accumulator);
+    eval_okay_test!(fromjson);
+    eval_okay_test!(fromjson_escapes);
+    eval_okay_test!(fromTOML);
+    eval_okay_test!(
+        #[ignore = "timestamps are not supported"]
+        fromTOML_timestamps
+    );
+    eval_okay_test!(functionargs);
+    eval_okay_test!(hashfile);
+    eval_okay_test!(hashstring);
+    eval_okay_test!(getattrpos);
+    eval_okay_test!(getattrpos_functionargs);
+    eval_okay_test!(getattrpos_undefined);
+    eval_okay_test!(getenv, || {
+        unsafe { std::env::set_var("TEST_VAR", "foo") };
+    });
+    eval_okay_test!(groupBy);
+    eval_okay_test!(r#if);
+    eval_okay_test!(ind_string);
+    eval_okay_test!(import);
+    eval_okay_test!(inherit_attr_pos);
+    eval_okay_test!(
+        #[ignore = "__overrides is not supported"]
+        inherit_from
+    );
+    eval_okay_test!(intersectAttrs);
+    eval_okay_test!(r#let);
+    eval_okay_test!(list);
+    eval_okay_test!(listtoattrs);
+    eval_okay_test!(logic);
+    eval_okay_test!(map);
+    eval_okay_test!(mapattrs);
+    eval_okay_test!(merge_dynamic_attrs);
+    eval_okay_test!(nested_with);
+    eval_okay_test!(new_let);
+    eval_okay_test!(null_dynamic_attrs);
+    eval_okay_test!(
+        #[ignore = "__overrides is not supported"]
+        overrides
+    );
+    eval_okay_test!(
+        #[ignore = "not implemented: parseFlakeRef"]
+        parse_flake_ref
+    );
+    eval_okay_test!(partition);
+    eval_okay_test!(path);
+    eval_okay_test!(pathexists);
+    eval_okay_test!(path_string_interpolation, || {
+        unsafe {
+            std::env::set_var("HOME", "/fake-home");
+        }
+    });
+    eval_okay_test!(patterns);
+    eval_okay_test!(print);
+    eval_okay_test!(readDir);
+    eval_okay_test!(readfile);
+    eval_okay_test!(readFileType);
+    eval_okay_test!(redefine_builtin);
+    eval_okay_test!(regex_match);
+    eval_okay_test!(regex_split);
+    eval_okay_test!(regression_20220122);
+    eval_okay_test!(regression_20220125);
+    eval_okay_test!(regrettable_rec_attrset_merge);
+    eval_okay_test!(remove);
+    eval_okay_test!(repeated_empty_attrs);
+    eval_okay_test!(repeated_empty_list);
+    eval_okay_test!(replacestrings);
+    eval_okay_test!(
+        #[ignore = "requires -I CLI flags"]
+        search_path
+    );
+    eval_okay_test!(scope_1);
+    eval_okay_test!(scope_2);
+    eval_okay_test!(scope_3);
+    eval_okay_test!(scope_4);
+    eval_okay_test!(scope_6);
+    eval_okay_test!(scope_7);
+    eval_okay_test!(seq);
+    eval_okay_test!(sort);
+    eval_okay_test!(splitversion);
+    eval_okay_test!(string);
+    eval_okay_test!(strings_as_attrs_names);
+    eval_okay_test!(substring);
+    eval_okay_test!(substring_context);
+    eval_okay_test!(symlink_resolution);
+    eval_okay_test!(
+        #[ignore = "TCO not implemented, also disabled in CppNix"]
+        tail_call_1
+    );
+    eval_okay_test!(tojson);
+    eval_okay_test!(toxml);
+    eval_okay_test!(toxml2);
+    eval_okay_test!(tryeval);
+    eval_okay_test!(types);
+    eval_okay_test!(versions);
+    eval_okay_test!(with);
+    eval_okay_test!(zipAttrsWith);
+}
+
+mod fail {
+    use super::*;
+
+    eval_fail_test!(abort);
+    eval_fail_test!(addDrvOutputDependencies_empty_context);
+    eval_fail_test!(addDrvOutputDependencies_multi_elem_context);
+    eval_fail_test!(addDrvOutputDependencies_wrong_element_kind);
+    eval_fail_test!(addErrorRuntime_example);
+    eval_fail_test!(assert);
+    eval_fail_test!(assert_equal_attrs_names);
+    eval_fail_test!(assert_equal_attrs_names_2);
+    eval_fail_test!(assert_equal_derivations);
+    eval_fail_test!(assert_equal_derivations_extra);
+    eval_fail_test!(assert_equal_floats);
+    eval_fail_test!(assert_equal_function_direct);
+    eval_fail_test!(assert_equal_int_float);
+    eval_fail_test!(assert_equal_ints);
+    eval_fail_test!(assert_equal_list_length);
+    eval_fail_test!(assert_equal_paths);
+    eval_fail_test!(assert_equal_type);
+    eval_fail_test!(assert_equal_type_nested);
+    eval_fail_test!(assert_nested_bool);
+    eval_fail_test!(attr_name_type);
+    eval_fail_test!(attrset_merge_drops_later_rec);
+    eval_fail_test!(bad_string_interpolation_1);
+    eval_fail_test!(bad_string_interpolation_2);
+    eval_fail_test!(bad_string_interpolation_3);
+    eval_fail_test!(bad_string_interpolation_4);
+    eval_fail_test!(blackhole);
+    eval_fail_test!(call_primop);
+    eval_fail_test!(deepseq);
+    eval_fail_test!(derivation_name);
+    eval_fail_test!(dup_dynamic_attrs);
+    eval_fail_test!(duplicate_traces);
+    eval_fail_test!(eol_1);
+    eval_fail_test!(eol_2);
+    eval_fail_test!(eol_3);
+    eval_fail_test!(fetchTree_negative);
+    eval_fail_test!(fetchurl_baseName);
+    eval_fail_test!(fetchurl_baseName_attrs);
+    eval_fail_test!(fetchurl_baseName_attrs_name);
+    eval_fail_test!(flake_ref_to_string_negative_integer);
+    eval_fail_test!(foldlStrict_strict_op_application);
+    eval_fail_test!(fromJSON_keyWithNullByte);
+    eval_fail_test!(fromJSON_overflowing);
+    eval_fail_test!(fromJSON_valueWithNullByte);
+    eval_fail_test!(fromTOML_keyWithNullByte);
+    eval_fail_test!(fromTOML_timestamps);
+    eval_fail_test!(fromTOML_valueWithNullByte);
+    eval_fail_test!(hashfile_missing);
+    eval_fail_test!(infinite_recursion_lambda);
+    eval_fail_test!(list);
+    eval_fail_test!(missing_arg);
+    eval_fail_test!(mutual_recursion);
+    eval_fail_test!(nested_list_items);
+    eval_fail_test!(nonexist_path);
+    eval_fail_test!(not_throws);
+    eval_fail_test!(overflowing_add);
+    eval_fail_test!(overflowing_div);
+    eval_fail_test!(overflowing_mul);
+    eval_fail_test!(overflowing_sub);
+    eval_fail_test!(path_slash);
+    eval_fail_test!(pipe_operators);
+    eval_fail_test!(recursion);
+    eval_fail_test!(remove);
+    eval_fail_test!(scope_5);
+    eval_fail_test!(seq);
+    eval_fail_test!(set);
+    eval_fail_test!(set_override);
+    eval_fail_test!(string_nul_1);
+    eval_fail_test!(string_nul_2);
+    eval_fail_test!(substring);
+    eval_fail_test!(toJSON);
+    eval_fail_test!(toJSON_non_utf_8);
+    eval_fail_test!(to_path);
+    eval_fail_test!(undeclared_arg);
+    eval_fail_test!(using_set_as_attr_name);
+}