implement import & scopedImport (WIP, ResolvePath resolves to string)

fix-builtins/src/lib.rs

@@ -244,6 +244,11 @@ pub enum PrimOpPhase {
 
     // TODO: split into separate enums
     CallPattern,
+    CallFunctor1,
+    CallFunctor2,
+
+    ImportFinalize,
+    ScopedImportFinalize,
 
     Illegal,
 }

fix-codegen/src/disassembler.rs

@@ -1,9 +1,10 @@
 use std::fmt::Write;
 
 use colored::Colorize;
+use fix_builtins::BuiltinId;
 use num_enum::TryFromPrimitive;
 
-use crate::{AttrKeyType, InstructionPtr, Op, OperandType};
+use crate::{InstructionPtr, Op, OperandType};
 
 pub trait DisassemblerContext {
     fn resolve_string(&self, id: u32) -> &str;
@@ -79,19 +80,30 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
 
     #[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 {
-            OperandType::Const => {
+            Const => {
                 self.read_u32();
             }
-            OperandType::Local => {
+            BigInt => {
+                self.read_i64();
+            }
+            Local => {
                 self.read_u8();
                 self.read_u32();
             }
-            OperandType::Builtins => {}
-            OperandType::BigInt => {
-                self.read_i64();
+            BuiltinConst => {
+                self.read_u32();
+            }
+            Builtins => {}
+            ReplBinding => {
+                self.read_u32();
+            }
+            ScopedImportBinding => {
+                self.read_u32();
+                self.read_u32();
             }
         }
     }
@@ -283,33 +295,32 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
             Op::Call => {
                 self.read_operand_data();
                 ("Call", "arg=?".into())
-            },
+            }
             Op::DispatchPrimOp => {
-                todo!();
+                let id = BuiltinId::try_from_primitive(self.read_u8()).expect("invalid builtin id");
+                ("DispatchPrimOp", format!("id={id:?}"))
             }
 
             Op::MakeAttrs => {
-                let count = self.read_u32();
-                let mut args = format!("size={}", count);
-                for _ in 0..count {
-                    let key_tag = self.read_u8();
-                    let key_ty =
-                        AttrKeyType::try_from_primitive(key_tag).expect("invalid attr key type");
-                    match key_ty {
-                        AttrKeyType::Static => {
+                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);
-                        }
-                        AttrKeyType::Dynamic => {
-                            let _ = write!(args, " [dyn");
-                            self.read_operand_data();
-                        }
-                    }
+                    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()),
@@ -412,19 +423,25 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
                 let force = self.read_u8();
                 ("ConcatStrings", format!("count={} force={}", count, force))
             }
-            Op::ResolvePath => ("ResolvePath", String::new()),
+            Op::CoerceToString => ("CoerceToString", String::new()),
+            Op::ResolvePath => {
+                let dir_id = self.read_u32();
+                let dir = self.ctx.resolve_string(dir_id);
+                ("ResolvePath", format!("dir={:?}", dir))
+            }
             Op::Assert => {
                 let raw_idx = self.read_u32();
                 let span_id = self.read_u32();
                 ("Assert", format!("text_id={} span={}", raw_idx, span_id))
             }
-            Op::PushWith => ("PushWith", String::new()),
-            Op::PopWith => ("PopWith", String::new()),
-            Op::PrepareWith => ("PrepareWith", String::new()),
             Op::LookupWith => {
                 let idx = self.read_u32();
                 let name = self.ctx.resolve_string(idx);
-                ("LookupWith", format!("{:?}", name))
+                let n = self.read_u8();
+                for _ in 0..n {
+                    self.read_operand_data();
+                }
+                ("LookupWith", format!("sym={:?} n={}", name, n))
             }
 
             Op::LoadBuiltins => ("LoadBuiltins", String::new()),
@@ -432,19 +449,16 @@ impl<'a, Ctx: DisassemblerContext> Disassembler<'a, Ctx> {
                 let id = self.read_u8();
                 ("LoadBuiltin", format!("id={}", id))
             }
-            Op::MkPos => {
-                let span_id = self.read_u32();
-                ("MkPos", format!("id={}", span_id))
-            }
             Op::LoadReplBinding => {
                 let idx = self.read_u32();
                 let name = self.ctx.resolve_string(idx);
                 ("LoadReplBinding", format!("{:?}", name))
             }
             Op::LoadScopedBinding => {
+                let slot = self.read_u32();
                 let idx = self.read_u32();
                 let name = self.ctx.resolve_string(idx);
-                ("LoadScopedBinding", format!("{:?}", name))
+                ("LoadScopedBinding", format!("slot={} {:?}", slot, name))
             }
             Op::Return => ("Return", String::new()),
             Op::Illegal => ("Illegal", String::new()),

fix-codegen/src/lib.rs

@@ -1,6 +1,4 @@
-use std::ops::Deref;
-
-use fix_builtins::BuiltinId;
+use fix_builtins::{BUILTINS, BuiltinId};
 use fix_common::StringId;
 use fix_ir::{Attr, BinOpKind, Ir, MaybeThunk, Param, RawIrRef, ThunkId, UnOpKind};
 use hashbrown::HashMap;
@@ -18,6 +16,8 @@ pub trait BytecodeContext {
     fn get_code(&self) -> &[u8];
     fn get_code_mut(&mut self) -> &mut Vec<u8>;
     fn add_constant(&mut self, val: Const) -> u32;
+    fn current_source_dir(&mut self) -> StringId;
+    fn current_scope_slot(&self) -> Option<u32>;
 }
 
 #[repr(u8)]
@@ -79,21 +79,18 @@ pub enum Op {
     JumpIfTrue,
     Jump,
 
+    CoerceToString,
+
     ConcatStrings,
     ResolvePath,
 
     Assert,
 
-    PushWith,
-    PopWith,
     LookupWith,
-    PrepareWith,
 
     LoadBuiltins,
     LoadBuiltin,
 
-    MkPos,
-
     LoadReplBinding,
     LoadScopedBinding,
 
@@ -103,7 +100,7 @@ pub enum Op {
 }
 
 struct ScopeInfo {
-    depth: u16,
+    depth: u8,
     thunk_map: HashMap<ThunkId, u32>,
 }
 
@@ -116,9 +113,12 @@ struct BytecodeEmitter<'a, Ctx: BytecodeContext> {
 #[derive(Debug, Clone, Copy, TryFromPrimitive)]
 pub enum OperandType {
     Const,
-    Local,
-    Builtins,
     BigInt,
+    Local,
+    BuiltinConst,
+    Builtins,
+    ReplBinding,
+    ScopedImportBinding,
 }
 
 pub enum Const {
@@ -126,6 +126,7 @@ pub enum Const {
     Float(f64),
     Bool(bool),
     String(StringId),
+    Path(StringId),
     PrimOp {
         id: BuiltinId,
         arity: u8,
@@ -143,9 +144,12 @@ pub enum AttrKeyType {
 
 pub enum InlineOperand {
     Const(Const),
-    Local { layer: u16, local: u32 },
-    Builtins,
     BigInt(i64),
+    Local { layer: u8, local: u32 },
+    BuiltinConst(StringId),
+    Builtins,
+    ReplBinding(StringId),
+    ScopedImportBinding(StringId),
 }
 
 pub fn compile_bytecode(ir: RawIrRef<'_>, ctx: &mut impl BytecodeContext) -> InstructionPtr {
@@ -164,12 +168,12 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
     }
 
     #[must_use]
-    fn inline_maybe_thunk(&self, val: MaybeThunk) -> InlineOperand {
+    fn inline_maybe_thunk(&self, val: &MaybeThunk) -> InlineOperand {
         use MaybeThunk::*;
-        match val {
+        match *val {
             Int(x) => {
-                if x <= i32::MAX as i64 {
-                    InlineOperand::Const(Const::Smi(x as i32))
+                if let Ok(x) = x.try_into() {
+                    InlineOperand::Const(Const::Smi(x))
                 } else {
                     InlineOperand::BigInt(x)
                 }
@@ -178,38 +182,65 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             Bool(b) => InlineOperand::Const(Const::Bool(b)),
             Null => InlineOperand::Const(Const::Null),
             Str(id) => InlineOperand::Const(Const::String(id)),
+            Path(id) => InlineOperand::Const(Const::String(id)),
             Thunk(id) => {
                 let (layer, local) = self.resolve_thunk(id);
                 InlineOperand::Local { layer, local }
             }
-            Arg { layer } => InlineOperand::Local {
-                layer: layer.try_into().expect("scope too deep!"),
-                local: 0,
-            },
-            _ => todo!(),
+            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) {
+    fn emit_maybe_thunk(&mut self, val: &MaybeThunk) {
+        use InlineOperand::*;
         let operand = self.inline_maybe_thunk(val);
         match operand {
-            InlineOperand::Const(val) => {
+            Const(val) => {
                 let idx = self.ctx.add_constant(val);
                 self.emit_u8(OperandType::Const as u8);
                 self.emit_u32(idx);
             }
-            InlineOperand::Local { layer, local } => {
-                self.emit_u8(OperandType::Local as u8);
-                self.emit_u8(layer as u8);
-                self.emit_u32(local);
-            }
-            InlineOperand::Builtins => {
-                self.emit_u8(OperandType::Builtins as u8);
-            }
-            InlineOperand::BigInt(val) => {
+            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);
+            }
         }
     }
 
@@ -218,6 +249,11 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         self.ctx.get_code_mut().push(op as u8);
     }
 
+    #[inline]
+    fn emit_bool(&mut self, val: bool) {
+        self.emit_u8(u8::from(val));
+    }
+
     #[inline]
     fn emit_u8(&mut self, val: u8) {
         self.ctx.get_code_mut().push(val);
@@ -289,11 +325,11 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             .extend_from_slice(&(id.0.to_usize() as u32).to_le_bytes());
     }
 
-    fn current_depth(&self) -> u16 {
+    fn current_depth(&self) -> u8 {
         self.scope_stack.last().map_or(0, |s| s.depth)
     }
 
-    fn resolve_thunk(&self, id: ThunkId) -> (u16, u32) {
+    fn resolve_thunk(&self, id: ThunkId) -> (u8, u32) {
         for scope in self.scope_stack.iter().rev() {
             if let Some(&local_idx) = scope.thunk_map.get(&id) {
                 let layer = self.current_depth() - scope.depth;
@@ -303,111 +339,19 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         panic!("ThunkId {:?} not found in any scope", id);
     }
 
-    fn emit_load(&mut self, layer: u16, local: u32) {
+    fn emit_load(&mut self, layer: u8, local: u32) {
         if layer == 0 {
             self.emit_op(Op::LoadLocal);
             self.emit_u32(local);
         } else {
             self.emit_op(Op::LoadOuter);
-            self.emit_u8(layer as u8);
+            self.emit_u8(layer);
             self.emit_u32(local);
         }
     }
 
-    fn count_with_thunks(&self, ir: RawIrRef<'_>) -> usize {
-        match ir.deref() {
-            Ir::With { thunks, body, .. } => thunks.len() + self.count_with_thunks(*body),
-            Ir::TopLevel { thunks, body } => thunks.len() + self.count_with_thunks(*body),
-            Ir::If { cond, consq, alter } => {
-                self.count_with_thunks(*cond)
-                    + self.count_with_thunks(*consq)
-                    + self.count_with_thunks(*alter)
-            }
-            Ir::BinOp { lhs, rhs, .. } => {
-                self.count_with_thunks(*lhs) + self.count_with_thunks(*rhs)
-            }
-            Ir::UnOp { rhs, .. } => self.count_with_thunks(*rhs),
-            Ir::Call { func, .. } => self.count_with_thunks(*func),
-            Ir::Assert {
-                assertion, expr, ..
-            } => self.count_with_thunks(*assertion) + self.count_with_thunks(*expr),
-            Ir::Select { expr, .. } => self.count_with_thunks(*expr),
-            Ir::HasAttr { lhs, .. } => self.count_with_thunks(*lhs),
-            Ir::ConcatStrings { parts, .. } => {
-                parts.iter().map(|p| self.count_with_thunks(*p)).sum()
-            }
-            _ => 0,
-        }
-    }
-
-    fn collect_all_thunks<'ir>(
-        &self,
-        own_thunks: &[(ThunkId, RawIrRef<'ir>)],
-        body: RawIrRef<'ir>,
-    ) -> Vec<(ThunkId, RawIrRef<'ir>)> {
-        let mut all = Vec::from(own_thunks);
-        self.collect_with_thunks_recursive(body, &mut all);
-        let mut i = 0;
-        while i < all.len() {
-            let thunk_body = all[i].1;
-            self.collect_with_thunks_recursive(thunk_body, &mut all);
-            i += 1;
-        }
-        all
-    }
-
-    fn collect_with_thunks_recursive<'ir>(
-        &self,
-        ir: RawIrRef<'ir>,
-        out: &mut Vec<(ThunkId, RawIrRef<'ir>)>,
-    ) {
-        match ir.deref() {
-            Ir::With { thunks, body, .. } => {
-                for &(id, inner) in thunks.iter() {
-                    out.push((id, inner));
-                }
-                self.collect_with_thunks_recursive(*body, out);
-            }
-            Ir::TopLevel { thunks, body } => {
-                for &(id, inner) in thunks.iter() {
-                    out.push((id, inner));
-                }
-                self.collect_with_thunks_recursive(*body, out);
-            }
-            Ir::If { cond, consq, alter } => {
-                self.collect_with_thunks_recursive(*cond, out);
-                self.collect_with_thunks_recursive(*consq, out);
-                self.collect_with_thunks_recursive(*alter, out);
-            }
-            Ir::BinOp { lhs, rhs, .. } => {
-                self.collect_with_thunks_recursive(*lhs, out);
-                self.collect_with_thunks_recursive(*rhs, out);
-            }
-            Ir::UnOp { rhs, .. } => self.collect_with_thunks_recursive(*rhs, out),
-            Ir::Call { func, .. } => {
-                self.collect_with_thunks_recursive(*func, out);
-            }
-            Ir::Assert {
-                assertion, expr, ..
-            } => {
-                self.collect_with_thunks_recursive(*assertion, out);
-                self.collect_with_thunks_recursive(*expr, out);
-            }
-            Ir::Select { expr, .. } => {
-                self.collect_with_thunks_recursive(*expr, out);
-            }
-            Ir::HasAttr { lhs, .. } => self.collect_with_thunks_recursive(*lhs, out),
-            Ir::ConcatStrings { parts, .. } => {
-                for p in parts.iter() {
-                    self.collect_with_thunks_recursive(*p, out);
-                }
-            }
-            _ => (),
-        }
-    }
-
     fn push_scope(&mut self, has_arg: bool, thunk_ids: &[ThunkId]) {
-        let depth = self.scope_stack.len() as u16;
+        let depth = self.scope_stack.len().try_into().expect("scope too deep!");
         let thunk_base = if has_arg { 1u32 } else { 0u32 };
         let thunk_map = thunk_ids
             .iter()
@@ -422,19 +366,13 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
     }
 
     fn emit_toplevel(&mut self, ir: RawIrRef<'_>) {
-        match ir.deref() {
+        match ir {
             &Ir::TopLevel { body, ref thunks } => {
-                let with_thunk_count = self.count_with_thunks(body);
-                let total_slots = thunks.len() + with_thunk_count;
-
-                let all_thunks = self.collect_all_thunks(thunks, body);
-                let thunk_ids: Vec<ThunkId> = all_thunks.iter().map(|&(id, _)| id).collect();
-
+                let thunk_ids: Vec<ThunkId> = thunks.iter().map(|&(id, _)| id).collect();
                 self.push_scope(false, &thunk_ids);
-
-                if total_slots > 0 {
+                if !thunks.is_empty() {
                     self.emit_op(Op::AllocLocals);
-                    self.emit_u32(total_slots as u32);
+                    self.emit_u32(thunks.len().try_into().expect("too many thunks"));
                 }
 
                 self.emit_scope_thunks(thunks);
@@ -468,11 +406,11 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
     }
 
     fn emit_expr(&mut self, ir: RawIrRef<'_>) {
-        match ir.deref() {
+        match ir {
             &Ir::Int(x) => {
-                if x <= i32::MAX as i64 {
+                if let Ok(x) = x.try_into() {
                     self.emit_op(Op::PushSmi);
-                    self.emit_i32(x as i32);
+                    self.emit_i32(x);
                 } else {
                     self.emit_op(Op::PushBigInt);
                     self.emit_i64(x);
@@ -492,6 +430,8 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             &Ir::Path(p) => {
                 self.emit_expr(p);
                 self.emit_op(Op::ResolvePath);
+                let dir_id = self.ctx.current_source_dir();
+                self.emit_str_id(dir_id);
             }
             &Ir::If { cond, consq, alter } => {
                 self.emit_expr(cond);
@@ -554,7 +494,7 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
                 self.emit_maybe_thunk(arg);
             }
             &Ir::Arg { layer } => {
-                self.emit_load(layer.try_into().expect("scope too deep!"), 0);
+                self.emit_load(layer, 0);
             }
             &Ir::TopLevel { body, ref thunks } => {
                 self.emit_toplevel_inner(body, thunks);
@@ -567,10 +507,6 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             } => {
                 self.emit_select(expr, attrpath, default, span);
             }
-            &Ir::Thunk(id) => {
-                let (layer, local) = self.resolve_thunk(id);
-                self.emit_load(layer, local);
-            }
             Ir::Builtins => {
                 self.emit_op(Op::LoadBuiltins);
             }
@@ -580,24 +516,23 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             }
             &Ir::BuiltinConst(id) => {
                 self.emit_select(
-                    RawIrRef(&Ir::Builtins),
+                    &Ir::Builtins,
                     &[Attr::Str(id, TextRange::default())],
                     None,
                     TextRange::default(),
                 );
             }
             &Ir::ConcatStrings {
-                parts: _,
-                force_string: _,
+                ref parts,
+                force_string,
             } => {
-                todo!("redesign ConcatStrings");
-                // self.emit_op(Op::ConcatStrings);
-                // self.emit_u16(parts.len() as u16);
-                // self.emit_u8(if force_string { 1 } else { 0 });
-                // for &part in parts.iter() {
-                //     let operand = self.inline_maybe_thunk(part);
-                //     self.emit_inline_operand(operand);
-                // }
+                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);
@@ -611,15 +546,10 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
                 let raw_idx = self.ctx.intern_string(assertion_raw);
                 let span_id = self.ctx.register_span(*span);
                 self.emit_expr(*assertion);
-                self.emit_expr(*expr);
                 self.emit_op(Op::Assert);
                 self.emit_str_id(raw_idx);
                 self.emit_u32(span_id);
-            }
-            &Ir::CurPos(span) => {
-                let span_id = self.ctx.register_span(span);
-                self.emit_op(Op::MkPos);
-                self.emit_u32(span_id);
+                self.emit_expr(*expr);
             }
             &Ir::ReplBinding(name) => {
                 self.emit_op(Op::LoadReplBinding);
@@ -627,21 +557,89 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
             }
             &Ir::ScopedImportBinding(name) => {
                 self.emit_op(Op::LoadScopedBinding);
+                let slot = self
+                    .ctx
+                    .current_scope_slot()
+                    .expect("ScopedImportBinding outside scoped compilation");
+                self.emit_u32(slot);
                 self.emit_str_id(name);
             }
-            &Ir::With {
-                namespace,
-                body,
-                ref thunks,
-            } => {
-                self.emit_with(namespace, body, thunks);
-            }
-            &Ir::WithLookup(name) => {
-                // TODO: specialize shallow with lookups
-                self.emit_op(Op::PrepareWith);
+            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);
+                    }
+                }
+            }
         }
     }
 
@@ -705,18 +703,6 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
                 let end_offset = (self.ctx.get_code_mut().len() as i32) - (after_jump as i32);
                 self.patch_i32(end_placeholder, end_offset);
             }
-            PipeL => {
-                todo!("new call");
-                // self.emit_expr(rhs);
-                // self.emit_expr(lhs);
-                // self.emit_op(Op::Call);
-            }
-            PipeR => {
-                todo!("new call");
-                // self.emit_expr(lhs);
-                // self.emit_expr(rhs);
-                // self.emit_op(Op::Call);
-            }
             _ => {
                 self.emit_expr(lhs);
                 self.emit_expr(rhs);
@@ -739,17 +725,13 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         }
     }
 
-    fn emit_func(
+    fn emit_func<'ir>(
         &mut self,
-        thunks: &[(ThunkId, RawIrRef<'_>)],
-        param: &Option<Param<'_>>,
-        body: RawIrRef<'_>,
+        thunks: &[(ThunkId, RawIrRef<'ir>)],
+        param: &Option<Param<'ir>>,
+        body: RawIrRef<'ir>,
     ) {
-        let with_thunk_count = self.count_with_thunks(body);
-        let total_slots = thunks.len() + with_thunk_count;
-
-        let all_thunks = self.collect_all_thunks(thunks, body);
-        let thunk_ids: Vec<ThunkId> = all_thunks.iter().map(|&(id, _)| id).collect();
+        let 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;
@@ -768,10 +750,10 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         {
             self.emit_op(Op::MakePatternClosure);
             self.emit_u32(entry_point);
-            self.emit_u32(total_slots as u32);
+            self.emit_u32(thunks.len().try_into().expect("too many thunks"));
             self.emit_u16(required.len() as u16);
             self.emit_u16(optional.len() as u16);
-            self.emit_u8(if *ellipsis { 1 } else { 0 });
+            self.emit_bool(*ellipsis);
 
             for &(sym, _) in required.iter() {
                 self.emit_str_id(sym);
@@ -787,33 +769,36 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         } else {
             self.emit_op(Op::MakeClosure);
             self.emit_u32(entry_point);
-            self.emit_u32(total_slots as u32);
+            self.emit_u32(thunks.len().try_into().expect("too many thunks"));
         }
     }
 
     fn emit_attrset(
         &mut self,
-        stcs: &fix_ir::HashMap<'_, StringId, (MaybeThunk, TextRange)>,
-        dyns: &[(RawIrRef<'_>, MaybeThunk, TextRange)],
+        stcs: &fix_ir::HashMap<'_, StringId, (&MaybeThunk, TextRange)>,
+        dyns: &[(RawIrRef<'_>, &MaybeThunk, TextRange)],
     ) {
         if stcs.is_empty() && dyns.is_empty() {
             self.emit_op(Op::MakeEmptyAttrs);
             return;
         }
 
-        let total = stcs.len() + dyns.len();
+        for &(key_expr, _val, _span) in dyns.iter() {
+            self.emit_expr(key_expr);
+        }
+
         self.emit_op(Op::MakeAttrs);
-        self.emit_u32(total as u32);
+        self.emit_u32(stcs.len() as u32);
+        self.emit_u32(dyns.len() as u32);
 
         for (&sym, &(val, span)) in stcs.iter() {
-            self.emit_u8(AttrKeyType::Static as u8);
             self.emit_str_id(sym);
             self.emit_maybe_thunk(val);
             let span_id = self.ctx.register_span(span);
             self.emit_u32(span_id);
         }
+
         for &(_key, val, span) in dyns.iter() {
-            self.emit_u8(AttrKeyType::Dynamic as u8);
             self.emit_maybe_thunk(val);
             let span_id = self.ctx.register_span(span);
             self.emit_u32(span_id);
@@ -911,19 +896,6 @@ impl<'a, Ctx: BytecodeContext> BytecodeEmitter<'a, Ctx> {
         self.emit_op(Op::HasAttrResolve);
     }
 
-    fn emit_with(
-        &mut self,
-        namespace: MaybeThunk,
-        body: RawIrRef<'_>,
-        thunks: &[(ThunkId, RawIrRef<'_>)],
-    ) {
-        self.emit_op(Op::PushWith);
-        self.emit_maybe_thunk(namespace);
-        self.emit_scope_thunks(thunks);
-        self.emit_expr(body);
-        self.emit_op(Op::PopWith);
-    }
-
     fn emit_toplevel_inner(&mut self, body: RawIrRef<'_>, thunks: &[(ThunkId, RawIrRef<'_>)]) {
         self.emit_scope_thunks(thunks);
         self.emit_expr(body);

fix-ir/src/downgrade.rs

@@ -39,12 +39,12 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, T, E: std::fmt::Display>
 }
 
 pub trait DowngradeContext<'id: 'ir, 'ir> {
-    fn new_expr(&self, expr: Ir<'ir, IrRef<'id, 'ir>>) -> IrRef<'id, 'ir>;
-    fn maybe_thunk(&mut self, ir: IrRef<'id, 'ir>) -> MaybeThunk;
+    fn new_expr(&self, expr: Ir<'ir, GhostRoRef<'id, 'ir>>) -> GhostRoIrRef<'id, 'ir>;
+    fn maybe_thunk(&mut self, ir: GhostRoIrRef<'id, 'ir>) -> GhostRoMaybeThunkRef<'id, 'ir>;
 
     fn intern_string(&mut self, sym: impl AsRef<str>) -> StringId;
     fn resolve_sym(&self, id: StringId) -> Symbol<'_>;
-    fn lookup(&self, sym: StringId, span: TextRange) -> Result<MaybeThunk>;
+    fn lookup(&mut self, sym: StringId, span: TextRange) -> Result<GhostRoMaybeThunkRef<'id, 'ir>>;
 
     fn get_current_source(&self) -> Source;
 
@@ -53,11 +53,11 @@ pub trait DowngradeContext<'id: 'ir, 'ir> {
         F: FnOnce(&mut Self) -> R;
     fn with_let_scope<F, R>(&mut self, bindings: &[StringId], f: F) -> Result<R>
     where
-        F: FnOnce(&mut Self) -> Result<(Vec<'ir, IrRef<'id, 'ir>>, R)>;
-    fn with_with_scope<F, R>(&mut self, f: F) -> R
+        F: FnOnce(&mut Self) -> Result<(Vec<'ir, GhostRoMaybeThunkRef<'id, 'ir>>, R)>;
+    fn with_with_scope<F, R>(&mut self, namespace: GhostRoMaybeThunkRef<'id, 'ir>, f: F) -> R
     where
         F: FnOnce(&mut Self) -> R;
-    fn with_thunk_scope<F, R>(&mut self, f: F) -> (R, Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>)
+    fn with_thunk_scope<F, R>(&mut self, f: F) -> (R, Vec<'ir, (ThunkId, GhostRoIrRef<'id, 'ir>)>)
     where
         F: FnOnce(&mut Self) -> R;
 
@@ -65,11 +65,11 @@ pub trait DowngradeContext<'id: 'ir, 'ir> {
 }
 
 pub trait Downgrade<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>>;
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>>;
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for Expr {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         use Expr::*;
         match self {
             Apply(apply) => apply.downgrade(ctx),
@@ -98,7 +98,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
             AttrSet(attrs) => attrs.downgrade(ctx),
             UnaryOp(op) => op.downgrade(ctx),
             Ident(ident) => ident.downgrade(ctx),
-            CurPos(curpos) => Ok(ctx.new_expr(Ir::CurPos(curpos.syntax().text_range()))),
+            CurPos(curpos) => curpos.downgrade(ctx),
             With(with) => with.downgrade(ctx),
             HasAttr(has) => has.downgrade(ctx),
             Paren(paren) => paren
@@ -114,7 +114,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Assert {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let assertion = self.condition().require(ctx, span)?;
         let assertion_raw = assertion.to_string();
@@ -130,7 +130,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::IfElse {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let cond = self.condition().require(ctx, span)?.downgrade(ctx)?;
         let consq = self.body().require(ctx, span)?.downgrade(ctx)?;
@@ -142,7 +142,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 macro_rules! path {
     ($ty:ident) => {
         impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::$ty {
-            fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+            fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
                 downgrade_path(self.parts(), ctx)
             }
         }
@@ -152,7 +152,7 @@ path!(PathAbs);
 path!(PathRel);
 path!(PathHome);
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::PathSearch {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let path = {
             let temp = self.content().require(ctx, span)?;
@@ -180,7 +180,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Str {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let normalized = self.normalized_parts();
         let is_single_literal = normalized.len() == 1
             && matches!(normalized.first(), Some(ast::InterpolPart::Literal(_)));
@@ -210,7 +210,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Literal {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let expr = match self.kind() {
             ast::LiteralKind::Integer(int) => Ir::Int(int.value().require(ctx, span)?),
@@ -225,16 +225,73 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Ident {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let text = self.ident_token().require(ctx, span)?.to_string();
         let sym = ctx.intern_string(text);
-        ctx.lookup(sym, span).map(|thunk| thunk.to_ir(ctx))
+        ctx.lookup(sym, span)
+            .map(|thunk| ctx.new_expr(Ir::MaybeThunk(thunk)))
+    }
+}
+
+impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::CurPos {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
+        fn byte_offset_to_line_col(content: &str, offset: usize) -> (u32, u32) {
+            let mut line = 1u32;
+            let mut col = 1u32;
+
+            for (idx, ch) in content.char_indices() {
+                if idx >= offset {
+                    break;
+                }
+                if ch == '\n' {
+                    line += 1;
+                    col = 1;
+                } else {
+                    col += 1;
+                }
+            }
+
+            (line, col)
+        }
+
+        let span = self.syntax().text_range();
+        let source = ctx.get_current_source();
+        let (line, column) = byte_offset_to_line_col(&source.src, span.start().into());
+
+        let file_sym = ctx.intern_string("file");
+        let line_sym = ctx.intern_string("line");
+        let column_sym = ctx.intern_string("column");
+
+        let file: GhostRoMaybeThunkRef = ctx
+            .bump()
+            .alloc(GhostCell::new(MaybeThunk::Str(ctx.intern_string(source.get_name()))).into());
+        let line = ctx
+            .bump()
+            .alloc(GhostCell::new(MaybeThunk::Int(i64::from(line))).into());
+        let column = ctx
+            .bump()
+            .alloc(GhostCell::new(MaybeThunk::Int(i64::from(column))).into());
+
+        let map = {
+            let mut map = HashMap::new_in(ctx.bump());
+
+            map.insert(file_sym, (file, TextRange::default()));
+            map.insert(line_sym, (line, TextRange::default()));
+            map.insert(column_sym, (column, TextRange::default()));
+
+            map
+        };
+
+        Ok(ctx.new_expr(Ir::AttrSet {
+            stcs: map,
+            dyns: Vec::new_in(ctx.bump()),
+        }))
     }
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::AttrSet {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let rec = self.rec_token().is_some();
         if !rec {
             let attrs = downgrade_attrs(self, ctx)?;
@@ -250,7 +307,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::List {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let bump = ctx.bump();
         let items = self
             .items()
@@ -264,17 +321,52 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::BinOp {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
+        use BinOpKind::*;
+        use ast::BinOpKind as Kind;
+
         let span = self.syntax().text_range();
         let lhs = self.lhs().require(ctx, span)?.downgrade(ctx)?;
         let rhs = self.rhs().require(ctx, span)?.downgrade(ctx)?;
-        let kind = self.operator().require(ctx, span)?.into();
+        let kind = match self.operator().require(ctx, span)? {
+            Kind::Concat => Con,
+            Kind::Update => Upd,
+            Kind::Add => Add,
+            Kind::Sub => Sub,
+            Kind::Mul => Mul,
+            Kind::Div => Div,
+            Kind::And => And,
+            Kind::Equal => Eq,
+            Kind::Implication => Impl,
+            Kind::Less => Lt,
+            Kind::LessOrEq => Leq,
+            Kind::More => Gt,
+            Kind::MoreOrEq => Geq,
+            Kind::NotEqual => Neq,
+            Kind::Or => Or,
+            Kind::PipeLeft => {
+                let arg = ctx.maybe_thunk(rhs);
+                return Ok(ctx.new_expr(Ir::Call {
+                    func: lhs,
+                    arg,
+                    span,
+                }));
+            }
+            Kind::PipeRight => {
+                let arg = ctx.maybe_thunk(lhs);
+                return Ok(ctx.new_expr(Ir::Call {
+                    func: rhs,
+                    arg,
+                    span,
+                }));
+            }
+        };
         Ok(ctx.new_expr(Ir::BinOp { lhs, rhs, kind }))
     }
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::HasAttr {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let lhs = self.expr().require(ctx, span)?.downgrade(ctx)?;
         let rhs = downgrade_attrpath(self.attrpath().require(ctx, span)?, ctx)?;
@@ -283,7 +375,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::UnaryOp {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let rhs = self.expr().require(ctx, span)?.downgrade(ctx)?;
         let kind = self.operator().require(ctx, span)?.into();
@@ -292,7 +384,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Select {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let expr = self.expr().require(ctx, span)?.downgrade(ctx)?;
         let attrpath = downgrade_attrpath(self.attrpath().require(ctx, span)?, ctx)?;
@@ -311,7 +403,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::LegacyLet {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let entries: Vec<'ir, _> = self.entries().collect_in(ctx.bump());
         let attrset_expr = downgrade_let_bindings(entries, ctx, |ctx, binding_keys| {
@@ -340,7 +432,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::LetIn {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let entries: Vec<'ir, _> = self.entries().collect_in(ctx.bump());
         let span = self.syntax().text_range();
         let body_expr = self.body().require(ctx, span)?;
@@ -350,33 +442,25 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::With {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let namespace = self.namespace().require(ctx, span)?.downgrade(ctx)?;
         let namespace = ctx.maybe_thunk(namespace);
 
         let body_expr = self.body().require(ctx, span)?;
-        let (body, thunks) =
-            ctx.with_thunk_scope(|ctx| ctx.with_with_scope(|ctx| body_expr.downgrade(ctx)));
-        let body = body?;
-
-        Ok(ctx.new_expr(Ir::With {
-            namespace,
-            body,
-            thunks,
-        }))
+        ctx.with_with_scope(namespace, |ctx| body_expr.downgrade(ctx))
     }
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Lambda {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let raw_param = self.param().require(ctx, span)?;
         let body_ast = self.body().require(ctx, span)?;
 
         struct Ret<'id, 'ir> {
             param: Option<Param<'ir>>,
-            body: IrRef<'id, 'ir>,
+            body: GhostRoIrRef<'id, 'ir>,
         }
 
         let (ret, thunks) = ctx.with_thunk_scope(|ctx| {
@@ -433,7 +517,7 @@ impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> fo
 }
 
 impl<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>> Downgrade<'id, 'ir, Ctx> for ast::Apply {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<IrRef<'id, 'ir>> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<GhostRoIrRef<'id, 'ir>> {
         let span = self.syntax().text_range();
         let func = self.lambda().require(ctx, span)?.downgrade(ctx)?;
         let arg = self.argument().require(ctx, span)?.downgrade(ctx)?;
@@ -835,8 +919,15 @@ fn make_attrpath_value_entry<'ir>(path: Vec<'ir, ast::Attr>, value: ast::Expr) -
 }
 
 struct FinalizedAttrSet<'id, 'ir> {
-    stcs: HashMap<'ir, StringId, (MaybeThunk, TextRange)>,
-    dyns: Vec<'ir, (IrRef<'id, 'ir>, MaybeThunk, TextRange)>,
+    stcs: HashMap<'ir, StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
+    dyns: Vec<
+        'ir,
+        (
+            GhostRoIrRef<'id, 'ir>,
+            GhostRoMaybeThunkRef<'id, 'ir>,
+            TextRange,
+        ),
+    >,
 }
 
 fn downgrade_attrs<'id, 'ir>(
@@ -851,7 +942,7 @@ fn downgrade_attrs<'id, 'ir>(
 fn downgrade_attr<'id, 'ir>(
     attr: ast::Attr,
     ctx: &mut impl DowngradeContext<'id, 'ir>,
-) -> Result<Attr<IrRef<'id, 'ir>>> {
+) -> Result<Attr<GhostRoIrRef<'id, 'ir>>> {
     use ast::Attr::*;
     use ast::InterpolPart::*;
     match attr {
@@ -912,7 +1003,7 @@ fn downgrade_attr<'id, 'ir>(
 fn downgrade_attrpath<'id, 'ir>(
     attrpath: ast::Attrpath,
     ctx: &mut impl DowngradeContext<'id, 'ir>,
-) -> Result<Vec<'ir, Attr<IrRef<'id, 'ir>>>> {
+) -> Result<Vec<'ir, Attr<GhostRoIrRef<'id, 'ir>>>> {
     let bump = ctx.bump();
     attrpath
         .attrs()
@@ -921,7 +1012,7 @@ fn downgrade_attrpath<'id, 'ir>(
 }
 
 struct PatternBindings<'id, 'ir> {
-    body: IrRef<'id, 'ir>,
+    body: GhostRoIrRef<'id, 'ir>,
     required: Vec<'ir, (StringId, TextRange)>,
     optional: Vec<'ir, (StringId, TextRange)>,
 }
@@ -930,7 +1021,7 @@ fn downgrade_pattern_bindings<'id, 'ir, Ctx>(
     pat_entries: impl Iterator<Item = ast::PatEntry>,
     alias: Option<StringId>,
     ctx: &mut Ctx,
-    body_fn: impl FnOnce(&mut Ctx, &[StringId]) -> Result<IrRef<'id, 'ir>>,
+    body_fn: impl FnOnce(&mut Ctx, &[StringId]) -> Result<GhostRoIrRef<'id, 'ir>>,
 ) -> Result<PatternBindings<'id, 'ir>>
 where
     Ctx: DowngradeContext<'id, 'ir>,
@@ -989,6 +1080,7 @@ where
     }
 
     let arg = ctx.new_expr(Ir::Arg { layer: 0 });
+    let arg_thunk = ctx.maybe_thunk(arg);
     ctx.with_let_scope(&keys, |ctx| {
         let vals = params
             .into_iter()
@@ -1000,21 +1092,16 @@ where
                     span,
                 } = param;
                 let default = default.map(|default| default.downgrade(ctx)).transpose()?;
-                // let default = if let Some(default) = default {
-                //     let default = default.clone().downgrade(ctx)?;
-                //     Some(ctx.maybe_thunk(default))
-                // } else {
-                //     None
-                // };
 
-                Ok(ctx.new_expr(Ir::Select {
+                let expr = ctx.new_expr(Ir::Select {
                     expr: arg,
                     attrpath: Vec::from_iter_in([Attr::Str(sym, sym_span)], bump),
                     default,
                     span,
-                }))
+                });
+                Ok(ctx.maybe_thunk(expr))
             })
-            .chain(alias.into_iter().map(|_| Ok(arg)))
+            .chain(alias.into_iter().map(|_| Ok(arg_thunk)))
             .collect_in::<Result<_>>(bump)?;
 
         let body = body_fn(ctx, &keys)?;
@@ -1034,10 +1121,10 @@ fn downgrade_let_bindings<'id, 'ir, Ctx, F>(
     entries: Vec<'ir, ast::Entry>,
     ctx: &mut Ctx,
     body_fn: F,
-) -> Result<IrRef<'id, 'ir>>
+) -> Result<GhostRoIrRef<'id, 'ir>>
 where
     Ctx: DowngradeContext<'id, 'ir>,
-    F: FnOnce(&mut Ctx, &[StringId]) -> Result<IrRef<'id, 'ir>>,
+    F: FnOnce(&mut Ctx, &[StringId]) -> Result<GhostRoIrRef<'id, 'ir>>,
 {
     downgrade_rec_attrs_impl::<_, _, false>(entries, ctx, |ctx, binding_keys, _dyns| {
         body_fn(ctx, binding_keys)
@@ -1047,7 +1134,7 @@ where
 fn downgrade_rec_bindings<'id, 'ir, Ctx>(
     entries: Vec<'ir, ast::Entry>,
     ctx: &mut Ctx,
-) -> Result<IrRef<'id, 'ir>>
+) -> Result<GhostRoIrRef<'id, 'ir>>
 where
     Ctx: DowngradeContext<'id, 'ir>,
 {
@@ -1068,14 +1155,18 @@ fn downgrade_rec_attrs_impl<'id, 'ir, Ctx, F, const ALLOW_DYN: bool>(
     entries: Vec<'ir, ast::Entry>,
     ctx: &mut Ctx,
     body_fn: F,
-) -> Result<IrRef<'id, 'ir>>
+) -> Result<GhostRoIrRef<'id, 'ir>>
 where
     Ctx: DowngradeContext<'id, 'ir>,
     F: FnOnce(
         &mut Ctx,
         &[StringId],
-        &[(IrRef<'id, 'ir>, MaybeThunk, TextRange)],
-    ) -> Result<IrRef<'id, 'ir>>,
+        &[(
+            GhostRoIrRef<'id, 'ir>,
+            GhostRoMaybeThunkRef<'id, 'ir>,
+            TextRange,
+        )],
+    ) -> Result<GhostRoIrRef<'id, 'ir>>,
 {
     let mut pending = PendingAttrSet::new_in(ctx.bump());
     pending.collect_entries(entries.iter().cloned(), ctx)?;
@@ -1090,7 +1181,7 @@ where
         let vals = {
             let mut temp = Vec::with_capacity_in(keys.len(), ctx.bump());
             for sym in &keys {
-                temp.push(finalized.stcs.get(sym).expect("WTF").0.to_ir(ctx));
+                temp.push(finalized.stcs.get(sym).expect("WTF").0);
             }
             temp
         };
@@ -1101,7 +1192,7 @@ where
 fn collect_inherit_lookups<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>>(
     entries: &[ast::Entry],
     ctx: &mut Ctx,
-) -> Result<HashMap<'ir, StringId, (MaybeThunk, TextRange)>> {
+) -> Result<HashMap<'ir, StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>> {
     let mut inherit_lookups = HashMap::new_in(ctx.bump());
     for entry in entries {
         if let ast::Entry::Inherit(inherit) = entry
@@ -1141,7 +1232,7 @@ fn collect_binding_syms<'id: 'ir, 'ir, Ctx: DowngradeContext<'id, 'ir>, const AL
 
 fn finalize_pending_set<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_DYN: bool>(
     pending: PendingAttrSet,
-    inherit_lookups: &HashMap<StringId, (MaybeThunk, TextRange)>,
+    inherit_lookups: &HashMap<StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
     ctx: &mut Ctx,
 ) -> Result<FinalizedAttrSet<'id, 'ir>> {
     let mut stcs = HashMap::new_in(ctx.bump());
@@ -1169,9 +1260,9 @@ fn finalize_pending_set<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_D
 
 fn finalize_pending_value<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW_DYN: bool>(
     value: PendingValue,
-    inherit_lookups: &HashMap<StringId, (MaybeThunk, TextRange)>,
+    inherit_lookups: &HashMap<StringId, (GhostRoMaybeThunkRef<'id, 'ir>, TextRange)>,
     ctx: &mut Ctx,
-) -> Result<IrRef<'id, 'ir>> {
+) -> Result<GhostRoIrRef<'id, 'ir>> {
     match value {
         PendingValue::Expr(expr) => expr.downgrade(ctx),
         PendingValue::InheritFrom(from_expr, sym, span) => {
@@ -1185,9 +1276,10 @@ fn finalize_pending_value<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW
         }
         PendingValue::InheritScope(sym, span) => {
             if let Some(&(expr, _)) = inherit_lookups.get(&sym) {
-                Ok(expr.to_ir(ctx))
+                Ok(ctx.new_expr(Ir::MaybeThunk(expr)))
             } else {
-                ctx.lookup(sym, span).map(|val| val.to_ir(ctx))
+                ctx.lookup(sym, span)
+                    .map(|val| ctx.new_expr(Ir::MaybeThunk(val)))
             }
         }
         PendingValue::Set(set) => {
@@ -1210,7 +1302,7 @@ fn finalize_pending_value<'id, 'ir, Ctx: DowngradeContext<'id, 'ir>, const ALLOW
 fn downgrade_path<'id, 'ir>(
     parts: impl IntoIterator<Item = ast::InterpolPart<ast::PathContent>>,
     ctx: &mut impl DowngradeContext<'id, 'ir>,
-) -> Result<IrRef<'id, 'ir>> {
+) -> Result<GhostRoIrRef<'id, 'ir>> {
     let bump = ctx.bump();
     let parts = parts
         .into_iter()

fix-ir/src/lib.rs

@@ -1,5 +1,5 @@
 use std::hash::Hash;
-use std::ops::Deref;
+use std::marker::PhantomData;
 
 use bumpalo::Bump;
 use bumpalo::collections::Vec;
@@ -10,56 +10,70 @@ use num_enum::TryFromPrimitive as _;
 use rnix::{TextRange, ast};
 use string_interner::DefaultStringInterner;
 
-use crate::downgrade::DowngradeContext;
-
 pub mod downgrade;
 
 pub type HashMap<'ir, K, V> = hashbrown::HashMap<K, V, hashbrown::DefaultHashBuilder, &'ir Bump>;
 
-#[repr(transparent)]
-#[derive(Clone, Copy)]
-pub struct IrRef<'id, 'ir>(&'ir GhostCell<'id, Ir<'ir, Self>>);
-
-impl<'id, 'ir> IrRef<'id, 'ir> {
-    pub fn new(ir: &'ir GhostCell<'id, Ir<'ir, Self>>) -> Self {
-        Self(ir)
-    }
-
-    pub fn alloc(bump: &'ir Bump, ir: Ir<'ir, Self>) -> Self {
-        Self(bump.alloc(GhostCell::new(ir)))
-    }
-
-    pub fn borrow<'a>(&'a self, token: &'a GhostToken<'id>) -> &'a Ir<'ir, Self> {
-        self.0.borrow(token)
-    }
+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.
-    ///
-    /// # Safety
-    /// The transmute is sound because:
-    /// - `GhostCell<'id, T>` is `#[repr(transparent)]` over `T`
-    /// - `IrRef<'id, 'ir>` is `#[repr(transparent)]` over
-    ///   `&'ir GhostCell<'id, Ir<'ir, Self>>`
-    /// - `RawIrRef<'ir>` is `#[repr(transparent)]` over `&'ir Ir<'ir, Self>`
-    /// - `Ir<'ir, Ref>` is `#[repr(C)]` and both ref types are pointer-sized
-    ///
-    /// Consuming the `GhostToken` guarantees no `borrow_mut` calls can occur
-    /// afterwards, so the shared `&Ir` references from `RawIrRef::Deref` can
-    /// never alias with mutable references.
-    pub fn freeze(self, _token: GhostToken<'id>) -> RawIrRef<'ir> {
-        unsafe { std::mem::transmute(self) }
+    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)]
-#[derive(Clone, Copy, Debug)]
-pub struct RawIrRef<'ir>(pub &'ir Ir<'ir, Self>);
+pub struct GhostRoCell<'id, T: ?Sized>(GhostCell<'id, T>);
 
-impl<'ir> Deref for RawIrRef<'ir> {
-    type Target = Ir<'ir, RawIrRef<'ir>>;
-    fn deref(&self) -> &Self::Target {
-        self.0
+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)
     }
 }
 
@@ -73,110 +87,117 @@ pub enum MaybeThunk {
     Str(StringId),
     Path(StringId),
     Thunk(ThunkId),
-    Arg { layer: usize },
+    Arg { layer: u8 },
     Builtin(BuiltinId),
+    BuiltinConst(StringId),
     Builtins,
     ReplBinding(StringId),
     ScopedImportBinding(StringId),
-    WithLookup(StringId),
 }
 
-impl MaybeThunk {
-    fn to_ir<'id, 'ir>(self, ctx: &mut impl DowngradeContext<'id, 'ir>) -> IrRef<'id, 'ir> {
-        use MaybeThunk::*;
-        let ir = match self {
-            Int(x) => Ir::Int(x),
-            Float(x) => Ir::Float(x),
-            Bool(x) => Ir::Bool(x),
-            Null => Ir::Null,
-            Str(x) => Ir::Str(x),
-            Path(x) => Ir::Path(ctx.new_expr(Ir::Str(x))),
-            Thunk(x) => Ir::Thunk(x),
-            Arg { layer } => Ir::Arg { layer },
-            Builtin(x) => Ir::Builtin(x),
-            Builtins => Ir::Builtins,
-            ReplBinding(x) => Ir::ReplBinding(x),
-            ScopedImportBinding(x) => Ir::ScopedImportBinding(x),
-            WithLookup(x) => Ir::WithLookup(x),
-        };
-        ctx.new_expr(ir)
+pub trait 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, Ref> {
+pub enum Ir<'ir, R: RefExt<'ir> + ?Sized + 'ir> {
     Int(i64),
     Float(f64),
     Bool(bool),
     Null,
     Str(StringId),
-    Path(Ref),
+    Path(R::IrRef),
     AttrSet {
-        stcs: HashMap<'ir, StringId, (MaybeThunk, TextRange)>,
-        dyns: Vec<'ir, (Ref, MaybeThunk, TextRange)>,
+        stcs: HashMap<'ir, StringId, (R::MaybeThunkRef, TextRange)>,
+        dyns: Vec<'ir, (R::IrRef, R::MaybeThunkRef, TextRange)>,
     },
     List {
-        items: Vec<'ir, MaybeThunk>,
+        items: Vec<'ir, R::MaybeThunkRef>,
     },
     ConcatStrings {
-        parts: Vec<'ir, Ref>,
+        parts: Vec<'ir, R::Ref<Ir<'ir, R>>>,
         force_string: bool,
     },
 
     // OPs
     UnOp {
-        rhs: Ref,
+        rhs: R::IrRef,
         kind: UnOpKind,
     },
     BinOp {
-        lhs: Ref,
-        rhs: Ref,
+        lhs: R::IrRef,
+        rhs: R::IrRef,
         kind: BinOpKind,
     },
     HasAttr {
-        lhs: Ref,
-        rhs: Vec<'ir, Attr<Ref>>,
+        lhs: R::IrRef,
+        rhs: Vec<'ir, Attr<R::IrRef>>,
     },
     Select {
-        expr: Ref,
-        attrpath: Vec<'ir, Attr<Ref>>,
-        default: Option<Ref>,
+        expr: R::IrRef,
+        attrpath: Vec<'ir, Attr<R::IrRef>>,
+        default: Option<R::IrRef>,
         span: TextRange,
     },
 
     // Conditionals
     If {
-        cond: Ref,
-        consq: Ref,
-        alter: Ref,
+        cond: R::IrRef,
+        consq: R::IrRef,
+        alter: R::IrRef,
     },
     Assert {
-        assertion: Ref,
-        expr: Ref,
+        assertion: R::IrRef,
+        expr: R::IrRef,
         assertion_raw: String,
         span: TextRange,
     },
 
-    With {
-        namespace: MaybeThunk,
-        body: Ref,
-        thunks: Vec<'ir, (ThunkId, Ref)>,
+    WithLookup {
+        sym: StringId,
+        namespaces: Vec<'ir, R::MaybeThunkRef>,
     },
-    WithLookup(StringId),
 
     // Function related
     Func {
-        body: Ref,
+        body: R::IrRef,
         param: Option<Param<'ir>>,
-        thunks: Vec<'ir, (ThunkId, Ref)>,
+        thunks: Vec<'ir, (ThunkId, R::IrRef)>,
     },
     Arg {
-        layer: usize,
+        layer: u8,
     },
     Call {
-        func: Ref,
-        arg: MaybeThunk,
+        func: R::IrRef,
+        arg: R::MaybeThunkRef,
         span: TextRange,
     },
 
@@ -187,11 +208,10 @@ pub enum Ir<'ir, Ref> {
 
     // Misc
     TopLevel {
-        body: Ref,
-        thunks: Vec<'ir, (ThunkId, Ref)>,
+        body: R::IrRef,
+        thunks: Vec<'ir, (ThunkId, R::IrRef)>,
     },
-    Thunk(ThunkId),
-    CurPos(TextRange),
+    MaybeThunk(R::MaybeThunkRef),
     ReplBinding(StringId),
     ScopedImportBinding(StringId),
 }
@@ -241,36 +261,6 @@ pub enum BinOpKind {
     // Set/String/Path operations
     Con, // List concatenation (`++`)
     Upd, // AttrSet update (`//`)
-
-    // Not standard, but part of rnix AST
-    PipeL,
-    PipeR,
-}
-
-impl From<ast::BinOpKind> for BinOpKind {
-    fn from(op: ast::BinOpKind) -> Self {
-        use BinOpKind::*;
-        use ast::BinOpKind as kind;
-        match op {
-            kind::Concat => Con,
-            kind::Update => Upd,
-            kind::Add => Add,
-            kind::Sub => Sub,
-            kind::Mul => Mul,
-            kind::Div => Div,
-            kind::And => And,
-            kind::Equal => Eq,
-            kind::Implication => Impl,
-            kind::Less => Lt,
-            kind::LessOrEq => Leq,
-            kind::More => Gt,
-            kind::MoreOrEq => Geq,
-            kind::NotEqual => Neq,
-            kind::Or => Or,
-            kind::PipeLeft => PipeL,
-            kind::PipeRight => PipeR,
-        }
-    }
 }
 
 /// The kinds of unary operations.
@@ -299,38 +289,38 @@ pub struct Param<'ir> {
 
 pub fn new_global_env(
     strings: &mut DefaultStringInterner,
-) -> hashbrown::HashMap<StringId, Ir<'static, RawIrRef<'static>>> {
+) -> hashbrown::HashMap<StringId, MaybeThunk> {
     let mut global_env = hashbrown::HashMap::new();
     let builtins_sym = StringId(strings.get_or_intern("builtins"));
-    global_env.insert(builtins_sym, Ir::Builtins);
+    global_env.insert(builtins_sym, MaybeThunk::Builtins);
 
     for (idx, &(name, _)) in BUILTINS.iter().enumerate() {
         let id = BuiltinId::try_from_primitive(idx as u8).expect("infallible");
         let name = StringId(strings.get_or_intern(name));
-        global_env.insert(name, Ir::Builtin(id));
+        global_env.insert(name, MaybeThunk::Builtin(id));
     }
 
     let consts = [
         (
             "__currentSystem",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("currentSystem"))),
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("currentSystem"))),
         ),
-        ("__langVersion", Ir::Int(6)),
+        ("__langVersion", MaybeThunk::Int(6)),
         (
             "__nixVersion",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("nixVersion"))),
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("nixVersion"))),
         ),
         (
             "__storeDir",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("storeDir"))),
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("storeDir"))),
         ),
         (
             "__nixPath",
-            Ir::BuiltinConst(StringId(strings.get_or_intern("nixPath"))),
+            MaybeThunk::BuiltinConst(StringId(strings.get_or_intern("nixPath"))),
         ),
-        ("null", Ir::Null),
-        ("true", Ir::Bool(true)),
-        ("false", Ir::Bool(false)),
+        ("null", MaybeThunk::Null),
+        ("true", MaybeThunk::Bool(true)),
+        ("false", MaybeThunk::Bool(false)),
     ];
 
     for (name, ir) in consts {

fix-vm/src/bytecode_reader.rs

@@ -3,7 +3,7 @@ use fix_common::StringId;
 use num_enum::TryFromPrimitive;
 use string_interner::Symbol as _;
 
-use crate::{AttrKeyData, OperandData, VmRuntimeCtx};
+use crate::{OperandData, VmRuntimeCtx};
 
 pub(crate) struct BytecodeReader<'a> {
     bytecode: &'a [u8],
@@ -103,29 +103,30 @@ impl<'a> BytecodeReader<'a> {
                 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::BigInt => {
-                let val = self.read_i64();
-                OperandData::BigInt(val)
+            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 }
             }
         }
-
-    #[inline(always)]
-    pub(crate) fn read_attr_key_data(&mut self) -> crate::AttrKeyData {
-        use fix_codegen::AttrKeyType;
-        let tag = self.read_u8();
-        let ty = AttrKeyType::try_from_primitive(tag)
-            .unwrap_or_else(|err| panic!("unknown key tag: {:#04x}", err.number));
-        match ty {
-            AttrKeyType::Static => AttrKeyData::Static(self.read_string_id()),
-            AttrKeyType::Dynamic => AttrKeyData::Dynamic,
-        }
     }
 
     pub(crate) fn pc(&self) -> usize {

fix-vm/src/dispatch_tailcall.rs

@@ -180,20 +180,18 @@ 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));
 
-tail_fn!(op_assert, (reader));
+tail_fn!(op_assert, (ctx, reader, mc));
 
-tail_fn!(op_push_with, (ctx, reader, mc));
-tail_fn!(op_pop_with, ());
 tail_fn!(op_lookup_with, (ctx, reader, mc));
-tail_fn!(op_prepare_with, ());
 
 tail_fn!(op_load_builtins, ());
 tail_fn!(op_load_builtin, (reader));
 
-tail_fn!(op_mk_pos, (reader));
 tail_fn!(op_load_repl_binding, (reader));
 tail_fn!(op_load_scoped_binding, (reader));
 
@@ -273,20 +271,18 @@ table! {
     JumpIfTrue            => op_jump_if_true,
     Jump                  => op_jump,
 
+    CoerceToString        => op_coerce_to_string,
+
     ConcatStrings         => op_concat_strings,
     ResolvePath           => op_resolve_path,
 
     Assert                => op_assert,
 
-    PushWith              => op_push_with,
-    PopWith               => op_pop_with,
     LookupWith            => op_lookup_with,
-    PrepareWith           => op_prepare_with,
 
     LoadBuiltins          => op_load_builtins,
     LoadBuiltin           => op_load_builtin,
 
-    MkPos                 => op_mk_pos,
     LoadReplBinding       => op_load_repl_binding,
     LoadScopedBinding     => op_load_scoped_binding,
 

fix-vm/src/instructions/arithmetic.rs

@@ -13,7 +13,7 @@ impl<'gc> crate::Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         mc: &Mutation<'gc>,
     ) -> Step {
-        let (lhs, rhs) = self.try_force::<(StrictValue, StrictValue)>(reader, mc)?;
+        let (lhs, rhs) = self.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
         if let (Some(ls), Some(rs)) = (ctx.get_string(lhs), ctx.get_string(rhs)) {
             let ns = Gc::new(mc, crate::NixString::new(format!("{ls}{rs}")));
             self.push(Value::new_gc(ns));
@@ -47,7 +47,7 @@ impl<'gc> crate::Vm<'gc> {
         int_op: fn(i64, i64) -> i64,
         float_op: fn(f64, f64) -> f64,
     ) -> Step {
-        let (lhs, rhs) = self.try_force::<(StrictValue, StrictValue)>(reader, mc)?;
+        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) => {
@@ -60,7 +60,7 @@ impl<'gc> crate::Vm<'gc> {
 
     #[inline(always)]
     pub(crate) fn op_div(&mut self, reader: &mut BytecodeReader<'_>, mc: &Mutation<'gc>) -> Step {
-        let (lhs, rhs) = self.try_force::<(StrictValue, StrictValue)>(reader, mc)?;
+        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(
@@ -86,7 +86,7 @@ impl<'gc> crate::Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         mc: &Mutation<'gc>,
     ) -> Step {
-        let (lhs, rhs) = self.try_force::<(StrictValue, StrictValue)>(reader, mc)?;
+        let (lhs, rhs) = self.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
         let eq = match self.values_equal(ctx, lhs, rhs) {
             Ok(eq) => eq,
             Err(e) => return self.finish_vm_err(e),
@@ -102,7 +102,7 @@ impl<'gc> crate::Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         mc: &Mutation<'gc>,
     ) -> Step {
-        let (lhs, rhs) = self.try_force::<(StrictValue, StrictValue)>(reader, mc)?;
+        let (lhs, rhs) = self.force_and_retry::<(StrictValue, StrictValue)>(reader, mc)?;
         let eq = match self.values_equal(ctx, lhs, rhs) {
             Ok(eq) => eq,
             Err(e) => return self.finish_vm_err(e),
@@ -158,7 +158,7 @@ impl<'gc> crate::Vm<'gc> {
         mc: &Mutation<'gc>,
         pred: fn(Ordering) -> bool,
     ) -> Step {
-        let (lhs, rhs) = self.try_force::<(StrictValue, StrictValue)>(reader, mc)?;
+        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),
@@ -171,7 +171,7 @@ impl<'gc> crate::Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         mc: &Mutation<'gc>,
     ) -> Step {
-        let (l, r) = self.try_force::<(Gc<List>, Gc<List>)>(reader, mc)?;
+        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());
@@ -190,14 +190,14 @@ impl<'gc> crate::Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         mc: &Mutation<'gc>,
     ) -> Step {
-        let (l, r) = self.try_force::<(Gc<AttrSet>, Gc<AttrSet>)>(reader, mc)?;
+        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.try_force::<NixNum>(reader, mc)?;
+        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)),
@@ -207,7 +207,7 @@ impl<'gc> crate::Vm<'gc> {
 
     #[inline(always)]
     pub(crate) fn op_not(&mut self, reader: &mut BytecodeReader<'_>, mc: &Mutation<'gc>) -> Step {
-        let rhs = self.try_force::<bool>(reader, mc)?;
+        let rhs = self.force_and_retry::<bool>(reader, mc)?;
         self.push(Value::new_inline(!rhs));
         Step::Continue(())
     }
@@ -249,8 +249,8 @@ impl<'gc> crate::Vm<'gc> {
             return Ok(true);
         }
         if let (Some(a), Some(b)) = (lhs.as_gc::<crate::AttrSet>(), rhs.as_gc::<crate::AttrSet>()) {
-            let a = a.entries.borrow();
-            let b = b.entries.borrow();
+            let a = &a.entries;
+            let b = &b.entries;
             if a.len() != b.len() {
                 return Ok(false);
             }
@@ -326,6 +326,9 @@ fn numeric_binop<'gc>(
         (Some(NixNum::Float(a)), Some(NixNum::Int(b))) => {
             Ok(Value::new_float(float_op(a, b as f64)))
         }
-        _ => Err(crate::vm_err("cannot perform arithmetic on non-numbers")),
+        _ => Err(crate::vm_err(format!(
+            "cannot perform arithmetic on non-numbers: {:?}",
+            (lhs.ty(), rhs.ty())
+        ))),
     }
 }

fix-vm/src/instructions/calls.rs

@@ -17,7 +17,7 @@ impl<'gc> crate::Vm<'gc> {
         arg: Value<'gc>,
         resume_pc: usize,
     ) -> Step {
-        let func = self.try_force::<StrictValue>(reader, mc)?;
+        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"));
         }
@@ -29,10 +29,8 @@ impl<'gc> crate::Vm<'gc> {
                 self.push(arg);
                 self.call_stack.push(CallFrame {
                     pc: resume_pc,
-                    stack_depth: 0,
                     thunk: None,
                     env: self.env,
-                    with_env: self.with_env,
                 });
                 reader.set_pc(PrimOpPhase::CallPattern.ip() as usize);
                 return Step::Continue(());
@@ -44,10 +42,8 @@ impl<'gc> crate::Vm<'gc> {
             let new_env = Gc::new(mc, RefLock::new(Env::with_arg(arg, n_locals, env)));
             self.call_stack.push(CallFrame {
                 pc: resume_pc,
-                stack_depth: 0,
                 thunk: None,
                 env: self.env,
-                with_env: self.with_env,
             });
             reader.set_pc(ip as usize);
             self.env = new_env;
@@ -56,10 +52,8 @@ impl<'gc> crate::Vm<'gc> {
                 self.push(arg);
                 self.call_stack.push(CallFrame {
                     pc: resume_pc,
-                    stack_depth: 0,
                     thunk: None,
                     env: self.env,
-                    with_env: self.with_env,
                 });
                 reader.set_pc(primop.dispatch_ip as usize)
             } else {
@@ -78,10 +72,8 @@ impl<'gc> crate::Vm<'gc> {
                 self.push(arg);
                 self.call_stack.push(CallFrame {
                     pc: resume_pc,
-                    stack_depth: 0,
                     thunk: None,
                     env: self.env,
-                    with_env: self.with_env,
                 });
                 reader.set_pc(app.primop.dispatch_ip as usize)
             } else {
@@ -91,8 +83,30 @@ impl<'gc> crate::Vm<'gc> {
                 };
                 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 {
-            todo!("call other types: {func:?}")
+            return self.finish_err(Error::eval_error(format!(
+                "attempt to call something which is not a function but {}",
+                func.ty()
+            )));
         }
         Step::Continue(())
     }
@@ -116,13 +130,11 @@ impl<'gc> crate::Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         mc: &Mutation<'gc>,
     ) -> Step {
-        let val = self.try_force::<StrictValue>(reader, mc)?;
+        let val = self.force_and_retry::<StrictValue>(reader, mc)?;
         let Some(CallFrame {
             pc: ret_pc,
-            stack_depth,
             thunk,
             env,
-            with_env,
         }) = self.call_stack.pop()
         else {
             match self.force_mode {
@@ -137,10 +149,8 @@ impl<'gc> crate::Vm<'gc> {
                     self.push(val.relax());
                     self.call_stack.push(CallFrame {
                         pc: PrimOpPhase::ForceResultDeepFinish.ip() as usize,
-                        stack_depth: 0,
                         thunk: None,
                         env: self.env,
-                        with_env: self.with_env,
                     });
                     self.call_depth += 1;
                     reader.set_pc(PrimOpPhase::DeepSeq.ip() as usize);
@@ -151,13 +161,11 @@ impl<'gc> crate::Vm<'gc> {
         reader.set_pc(ret_pc);
         if let Some(outer_thunk) = thunk {
             *outer_thunk.borrow_mut(mc) = ThunkState::Evaluated(val);
-            self.replace(stack_depth, val.relax());
         } else {
             self.call_depth -= 1;
             self.push(val.relax())
         }
         self.env = env;
-        self.with_env = with_env;
         Step::Continue(())
     }
 }

fix-vm/src/instructions/closures.rs

@@ -15,7 +15,6 @@ impl<'gc> crate::Vm<'gc> {
             RefLock::new(ThunkState::Pending {
                 ip: entry_point as usize,
                 env: self.env,
-                with_env: self.with_env,
             }),
         );
         self.push(Value::new_gc(thunk));

fix-vm/src/instructions/collections.rs

@@ -5,8 +5,7 @@ use smallvec::SmallVec;
 
 use crate::value::NixType;
 use crate::{
-    AttrKeyData, AttrSet, BytecodeReader, List, OperandData, Step, StrictValue, Value,
-    VmRuntimeCtx, VmRuntimeCtxExt,
+    AttrSet, BytecodeReader, List, Step, StrictValue, Value, VmRuntimeCtx, VmRuntimeCtxExt,
 };
 
 impl<'gc> crate::Vm<'gc> {
@@ -17,25 +16,46 @@ impl<'gc> crate::Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         mc: &gc_arena::Mutation<'gc>,
     ) -> Step {
-        let count = reader.read_u32() as usize;
-        let mut entries: SmallVec<[AttrEntry; 4]> = SmallVec::with_capacity(count);
-        for _ in 0..count {
-            let key = reader.read_attr_key_data();
-            let val = reader.read_operand_data(ctx);
-            let _span_id = reader.read_u32();
-            entries.push(AttrEntry { key, val });
-        }
-        let mut kv: SmallVec<[(crate::StringId, Value); 4]> = SmallVec::with_capacity(count);
-        for entry in &entries {
-            let key_sid = match &entry.key {
-                AttrKeyData::Static(sid) => *sid,
-                AttrKeyData::Dynamic => {
-                    todo!()
+        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),
             };
-            let val = entry.val.resolve(mc, self);
-            kv.push((key_sid, val));
+            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 = reader.read_operand_data(ctx).resolve(mc, self);
+            let _span_id = reader.read_u32();
+            kv.push((key, val));
+        }
+
+        for key in dyn_keys {
+            let val = reader.read_operand_data(ctx).resolve(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));
@@ -58,7 +78,7 @@ impl<'gc> crate::Vm<'gc> {
         let _span_id = reader.read_u32();
         let key = reader.read_string_id();
 
-        let attrset = self.try_force::<Gc<AttrSet>>(reader, mc)?;
+        let attrset = self.force_and_retry::<Gc<AttrSet>>(reader, mc)?;
 
         match attrset.lookup(key) {
             Some(v) => {
@@ -78,7 +98,7 @@ impl<'gc> crate::Vm<'gc> {
     ) -> Step {
         let _span_id = reader.read_u32();
 
-        let (attrset, key_val) = self.try_force::<(Gc<AttrSet>, StrictValue)>(reader, mc)?;
+        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,
@@ -174,7 +194,7 @@ impl<'gc> crate::Vm<'gc> {
         let _span_id = reader.read_u32();
         let key = reader.read_string_id();
 
-        let current = self.try_force::<StrictValue>(reader, mc)?;
+        let current = self.force_and_retry::<StrictValue>(reader, mc)?;
 
         match current
             .as_gc::<AttrSet>()
@@ -197,7 +217,7 @@ impl<'gc> crate::Vm<'gc> {
     ) -> Step {
         let _span_id = reader.read_u32();
 
-        let (current, key_val) = self.try_force::<(StrictValue, StrictValue)>(reader, mc)?;
+        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,
@@ -237,7 +257,7 @@ impl<'gc> crate::Vm<'gc> {
         mc: &gc_arena::Mutation<'gc>,
     ) -> Step {
         let key = reader.read_string_id();
-        let current = self.try_force::<StrictValue>(reader, mc)?;
+        let current = self.force_and_retry::<StrictValue>(reader, mc)?;
 
         self.push(Value::new_inline(
             current
@@ -258,7 +278,7 @@ impl<'gc> crate::Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         mc: &gc_arena::Mutation<'gc>,
     ) -> Step {
-        let (current, dyn_key) = self.try_force::<(StrictValue, StrictValue)>(reader, mc)?;
+        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,
@@ -312,8 +332,3 @@ impl<'gc> crate::Vm<'gc> {
         Step::Continue(())
     }
 }
-
-pub(crate) struct AttrEntry {
-    pub(crate) key: AttrKeyData,
-    pub(crate) val: OperandData,
-}

fix-vm/src/instructions/control.rs

@@ -1,5 +1,8 @@
+use fix_error::Error;
+use gc_arena::Mutation;
+
 use crate::value::*;
-use crate::{BytecodeReader, Step};
+use crate::{BytecodeReader, Step, VmRuntimeCtx};
 
 impl<'gc> crate::Vm<'gc> {
     #[inline(always)]
@@ -9,7 +12,7 @@ impl<'gc> crate::Vm<'gc> {
         mc: &gc_arena::Mutation<'gc>,
     ) -> Step {
         let offset = reader.read_i32();
-        let cond = self.try_force::<StrictValue>(reader, mc)?;
+        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);
         }
@@ -20,10 +23,10 @@ impl<'gc> crate::Vm<'gc> {
     pub(crate) fn op_jump_if_true(
         &mut self,
         reader: &mut BytecodeReader<'_>,
-        mc: &gc_arena::Mutation<'gc>,
+        mc: &Mutation<'gc>,
     ) -> Step {
         let offset = reader.read_i32();
-        let cond = self.try_force::<StrictValue>(reader, mc)?;
+        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);
         }
@@ -38,9 +41,20 @@ impl<'gc> crate::Vm<'gc> {
     }
 
     #[inline(always)]
-    pub(crate) fn op_assert(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
-        let _raw_idx = reader.read_u32();
+    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();
-        todo!("implement Assert (force TOS)");
+        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/misc.rs

@@ -1,7 +1,12 @@
+use std::path::{Component, PathBuf};
+
 use fix_builtins::BuiltinId;
+use fix_common::StringId;
+use fix_error::Error;
 use num_enum::TryFromPrimitive;
 
-use crate::{BytecodeReader, PrimOp, Step, Value, VmRuntimeCtx};
+use crate::value::{AttrSet, NixString, StrictValue};
+use crate::{BytecodeReader, PrimOp, Step, Value, VmRuntimeCtx, VmRuntimeCtxExt};
 
 impl<'gc> crate::Vm<'gc> {
     #[inline(always)]
@@ -22,12 +27,6 @@ impl<'gc> crate::Vm<'gc> {
         Step::Continue(())
     }
 
-    #[inline(always)]
-    pub(crate) fn op_mk_pos(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
-        let _span_id = reader.read_u32();
-        todo!("MkPos");
-    }
-
     #[inline(always)]
     pub(crate) fn op_load_repl_binding(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
         let _name = reader.read_string_id();
@@ -35,9 +34,51 @@ impl<'gc> crate::Vm<'gc> {
     }
 
     #[inline(always)]
-    pub(crate) fn op_load_scoped_binding(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
-        let _name = reader.read_string_id();
-        todo!("LoadScopedBinding");
+    pub(crate) fn op_load_scoped_binding(
+        &mut self,
+        ctx: &impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+    ) -> 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 {
+            todo!("coerce other types to string: {:?}", val.ty());
+        }
+        Step::Continue(())
     }
 
     #[inline(always)]
@@ -47,18 +88,89 @@ impl<'gc> crate::Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         _mc: &gc_arena::Mutation<'gc>,
     ) -> Step {
-        let _parts_count = reader.read_u16() as usize;
+        let count = reader.read_u16() as usize;
         let _force_string = reader.read_u8() != 0;
-        let mut _operands: smallvec::SmallVec<[crate::OperandData; 4]> =
-            smallvec::SmallVec::with_capacity(_parts_count);
-        for _ in 0.._parts_count {
-            _operands.push(reader.read_operand_data(ctx));
+
+        let mut total_len = 0;
+        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();
         }
-        todo!("implement ConcatStrings (force parts, coerce to string, concatenate)");
+
+        let mut result = String::with_capacity(total_len);
+        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);
+        }
+
+        self.stack.truncate(self.stack.len() - count);
+
+        let sid = ctx.intern_string(result);
+        self.push(Value::new_inline(sid));
+        Step::Continue(())
     }
 
     #[inline(always)]
-    pub(crate) fn op_resolve_path(&mut self, _ctx: &mut impl VmRuntimeCtx) -> Step {
-        todo!("implement ResolvePath");
+    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();
+        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(sid));
+        Step::Continue(())
     }
 }
+
+/// Resolve a Nix path literal against `current_dir`.
+///
+/// Mirrors nix-js's `op_resolve_path`: absolute paths returned as-is, `~/X`
+/// expanded against `$HOME`, otherwise joined onto `current_dir`. The result
+/// is normalized by removing `.` components and resolving `..` lexically
+/// (no symlink resolution).
+fn resolve_path_str(current_dir: &str, path: &str) -> Result<String, Box<Error>> {
+    let raw = if path.starts_with('/') {
+        return Ok(path.to_owned());
+    } else if let Some(rest) = path.strip_prefix("~/") {
+        #[allow(deprecated)]
+        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
+    };
+    let mut normalized = PathBuf::new();
+    for component in raw.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),
+        }
+    }
+    Ok(normalized.to_string_lossy().into_owned())
+}

fix-vm/src/instructions/mod.rs

@@ -1,5 +1,4 @@
 pub(crate) mod arithmetic;
-pub(crate) mod builtins;
 pub(crate) mod calls;
 pub(crate) mod closures;
 pub(crate) mod collections;

fix-vm/src/instructions/with_scope.rs

@@ -1,51 +1,11 @@
 use fix_common::Symbol;
 use fix_error::Error;
-use gc_arena::Gc;
+use smallvec::SmallVec;
 
 use crate::value::*;
-use crate::{BytecodeReader, CallFrame, Step, VmRuntimeCtx, WithEnv};
+use crate::{Break, BytecodeReader, CallFrame, Step, VmRuntimeCtx};
 
 impl<'gc> crate::Vm<'gc> {
-    #[inline(always)]
-    pub(crate) fn op_push_with(
-        &mut self,
-        ctx: &mut impl VmRuntimeCtx,
-        reader: &mut BytecodeReader<'_>,
-        mc: &gc_arena::Mutation<'gc>,
-    ) -> Step {
-        let env = reader.read_operand_data(ctx).resolve(mc, self);
-        let scope = Gc::new(
-            mc,
-            WithEnv {
-                env,
-                prev: self.with_env,
-            },
-        );
-        self.with_env = Some(scope);
-        Step::Continue(())
-    }
-
-    #[inline(always)]
-    pub(crate) fn op_pop_with(&mut self) -> Step {
-        let Some(scope) = self.with_env else {
-            unreachable!("no with_scope to pop");
-        };
-        self.with_env = scope.prev;
-        Step::Continue(())
-    }
-
-    #[inline(always)]
-    pub(crate) fn op_prepare_with(&mut self) -> Step {
-        self.call_stack.push(CallFrame {
-            pc: usize::MAX,
-            stack_depth: 0,
-            thunk: None,
-            env: self.env,
-            with_env: self.with_env,
-        });
-        Step::Continue(())
-    }
-
     #[inline(always)]
     pub(crate) fn op_lookup_with(
         &mut self,
@@ -53,31 +13,66 @@ impl<'gc> crate::Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         mc: &gc_arena::Mutation<'gc>,
     ) -> Step {
-        let name = reader.read_string_id();
+        #[allow(clippy::unwrap_used)]
+        let counter = self.peek_forced(0).as_inline::<i32>().unwrap();
 
-        let Some(&WithEnv { env, prev }) = self.with_env.as_deref() else {
-            let Some(CallFrame { with_env, .. }) = self.call_stack.pop() else {
-                unreachable!()
+        let name = reader.read_string_id();
+        let n = reader.read_u8();
+        let mut namespaces = SmallVec::<[_; 2]>::new();
+        for _ in 0..n {
+            namespaces.push(reader.read_operand_data(ctx).resolve(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"));
+                    }
+                }
+            }
         };
-            self.with_env = with_env;
+
+        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))
             )));
-        };
-        self.push(env);
-        let env = self.try_force::<Gc<AttrSet>>(reader, mc)?;
-        let Some(val) = env.lookup(name) else {
-            reader.set_pc(reader.inst_start_pc());
-            self.with_env = prev;
-            return Step::Continue(());
-        };
+        } else {
+            self.replace(0, Value::new_inline(counter + 1));
+            reader.set_pc(resume_pc);
+        }
 
-        self.push(val);
-        let Some(CallFrame { with_env, .. }) = self.call_stack.pop() else {
-            unreachable!()
-        };
-        self.with_env = with_env;
         Step::Continue(())
     }
 }

fix-vm/src/lib.rs

@@ -26,10 +26,11 @@ mod value;
 pub use value::StaticValue;
 use value::*;
 mod helpers;
-pub(crate) mod instructions;
-pub(crate) use bytecode_reader::BytecodeReader;
-pub(crate) use forced::Forced;
+mod instructions;
+use bytecode_reader::BytecodeReader;
+use forced::Forced;
 use helpers::*;
+mod primops;
 
 type VmResult<T> = std::result::Result<T, VmError>;
 
@@ -76,14 +77,26 @@ pub trait VmRuntimeCtx {
 
 pub trait VmCode {
     fn bytecode(&self) -> &[u8];
-    fn compile(
+    fn compile_with_scope(
         &mut self,
         source: Source,
+        extra_scope: Option<ExtraScope>,
         ctx: &mut impl VmRuntimeCtx,
     ) -> fix_error::Result<InstructionPtr>;
 }
 
-pub(crate) trait VmRuntimeCtxExt: VmRuntimeCtx {
+/// 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,
+    },
+}
+
+trait VmRuntimeCtxExt: VmRuntimeCtx {
     fn get_string<'a, 'gc: 'a>(&'a self, val: StrictValue<'gc>) -> Option<&'a str>;
     fn get_string_id<'a, 'gc: 'a>(
         &'a mut self,
@@ -143,14 +156,14 @@ impl<T: VmRuntimeCtx> ConvertValueWithSeen for T {
             Value::String(ns.as_str().to_owned())
         } else if let Some(attrs) = val.as_gc::<AttrSet>() {
             let bits = val.to_bits();
-            if attrs.entries.borrow().is_empty() {
+            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.borrow().iter() {
+            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);
@@ -193,50 +206,80 @@ impl<T: VmRuntimeCtx> ConvertValueWithSeen for T {
 }
 
 #[repr(u8)]
-pub(crate) enum Break {
+enum Break {
     Force,
     Done,
+    LoadFile,
 }
 
-pub(crate) type Step = std::ops::ControlFlow<Break>;
+type Step = std::ops::ControlFlow<Break>;
 
 #[derive(Collect)]
 #[collect(no_drop)]
 pub struct Vm<'gc> {
-    pub(crate) stack: Vec<Value<'gc>>,
-    pub(crate) call_stack: Vec<CallFrame<'gc>>,
-    pub(crate) call_depth: usize,
+    stack: Vec<Value<'gc>>,
+    call_stack: Vec<CallFrame<'gc>>,
+    call_depth: usize,
     #[allow(dead_code)]
     #[collect(require_static)]
-    pub(crate) error_context: Vec<ErrorFrame>,
+    error_context: Vec<ErrorFrame>,
 
-    pub(crate) env: GcEnv<'gc>,
-    pub(crate) with_env: Option<GcWithEnv<'gc>>,
+    env: GcEnv<'gc>,
 
-    pub(crate) import_cache: HashMap<PathBuf, Value<'gc>>,
+    import_cache: HashMap<PathBuf, Value<'gc>>,
+    /// Stack of attrsets, one per `scopedImport` invocation. Indexed by
+    /// `slot_id` baked into the bytecode at compile time. Slots are never
+    /// freed — they live for the lifetime of the [`Vm`] (i.e. one
+    /// `Vm::run` call).
+    scope_slots: Vec<Value<'gc>>,
 
-    pub(crate) builtins: Value<'gc>,
-    pub(crate) empty_list: Value<'gc>,
-    pub(crate) empty_attrs: Value<'gc>,
+    builtins: Value<'gc>,
+    empty_list: Value<'gc>,
+    empty_attrs: Value<'gc>,
 
-    pub(crate) force_mode: ForceMode,
+    force_mode: ForceMode,
 
     #[collect(require_static)]
-    pub(crate) result: Option<Result<fix_common::Value>>,
+    result: Option<Result<fix_common::Value>>,
+
+    /// Set by `import` / `scopedImport` primops just before they yield
+    /// `Break::LoadFile`. The outer [`Vm::run`] loop consumes it via
+    /// `Action::LoadFile`.
+    #[collect(require_static)]
+    pending_load: Option<PendingLoad>,
+
+    functor_sym: StringId,
 }
 
-pub(crate) enum OperandData {
+#[derive(Debug)]
+pub(crate) struct PendingLoad {
+    pub path: PathBuf,
+    pub scope: Option<PendingScope>,
+}
+
+#[derive(Debug)]
+pub(crate) struct PendingScope {
+    pub keys: HashSet<StringId>,
+    pub slot_id: u32,
+}
+
+enum OperandData {
     Const(StaticValue),
-    Local { layer: u8, idx: u32 },
-    Builtins,
     BigInt(i64),
+    Local { layer: u8, idx: u32 },
+    BuiltinConst(StringId),
+    Builtins,
+    ReplBinding(StringId),
+    ScopedImportBinding { slot_id: u32, name: StringId },
 }
 
 impl OperandData {
-    pub(crate) fn resolve<'gc>(&self, mc: &Mutation<'gc>, root: &Vm<'gc>) -> Value<'gc> {
+    fn resolve<'gc>(&self, mc: &Mutation<'gc>, root: &Vm<'gc>) -> Value<'gc> {
+        use OperandData::*;
         match *self {
-            OperandData::Const(sv) => sv.into(),
-            OperandData::Local { layer, idx } => {
+            Const(sv) => sv.into(),
+            BigInt(val) => Value::new_gc(Gc::new(mc, val)),
+            Local { layer, idx } => {
                 let mut cur = root.env;
                 for _ in 0..layer {
                     let prev = cur.borrow().prev.expect("env chain too short");
@@ -244,15 +287,28 @@ impl OperandData {
                 }
                 cur.borrow().locals[idx as usize]
             }
-            OperandData::Builtins => root.builtins,
-            OperandData::BigInt(val) => Value::new_gc(Gc::new(mc, val)),
+            #[allow(clippy::unwrap_used)]
+            BuiltinConst(id) => root
+                .builtins
+                .as_gc::<AttrSet>()
+                .unwrap()
+                .lookup(id)
+                .unwrap(),
+            Builtins => root.builtins,
+            ReplBinding(_id) => todo!(),
+            ScopedImportBinding { slot_id, name } => {
+                #[allow(clippy::unwrap_used)]
+                let scope = root
+                    .scope_slots
+                    .get(slot_id as usize)
+                    .expect("invalid scope slot");
+                #[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")
             }
         }
     }
-
-pub(crate) enum AttrKeyData {
-    Static(StringId),
-    Dynamic,
 }
 
 fn init_builtins<'gc>(mc: &Mutation<'gc>, ctx: &mut impl VmRuntimeCtx) -> Value<'gc> {
@@ -322,9 +378,9 @@ impl<'gc> Vm<'gc> {
             error_context: Vec::with_capacity(1024),
 
             env: Gc::new(mc, RefLock::new(Env::empty())),
-            with_env: None,
 
             import_cache: HashMap::new(),
+            scope_slots: Vec::new(),
 
             builtins,
             empty_list: Value::new_gc(Gc::new(mc, List::default())),
@@ -333,23 +389,26 @@ impl<'gc> Vm<'gc> {
             force_mode,
 
             result: None,
+            pending_load: None,
+
+            functor_sym: ctx.intern_string("__functor"),
         }
     }
 
     #[inline(always)]
-    pub(crate) fn finish_ok(&mut self, val: fix_common::Value) -> Step {
+    fn finish_ok(&mut self, val: fix_common::Value) -> Step {
         self.result = Some(Ok(val));
         Step::Break(Break::Done)
     }
 
     #[inline(always)]
-    pub(crate) fn finish_err(&mut self, err: Box<Error>) -> Step {
+    fn finish_err(&mut self, err: Box<Error>) -> Step {
         self.result = Some(Err(err));
         Step::Break(Break::Done)
     }
 
     #[inline(always)]
-    pub(crate) fn finish_type_err(&mut self, expected: NixType, got: NixType) -> Step {
+    fn finish_type_err(&mut self, expected: NixType, got: NixType) -> Step {
         self.result = Some(Err(Error::eval_error(format!(
             "expected {expected}, got {got}"
         ))));
@@ -357,24 +416,24 @@ impl<'gc> Vm<'gc> {
     }
 
     #[inline(always)]
-    pub(crate) fn finish_vm_err(&mut self, err: VmError) -> Step {
+    fn finish_vm_err(&mut self, err: VmError) -> Step {
         self.finish_err(err.into_error())
     }
 
     #[inline(always)]
-    pub(crate) fn push(&mut self, val: Value<'gc>) {
+    fn push(&mut self, val: Value<'gc>) {
         self.stack.push(val);
     }
 
     #[inline(always)]
     #[must_use]
-    pub(crate) fn pop(&mut self) -> Value<'gc> {
+    fn pop(&mut self) -> Value<'gc> {
         self.stack.pop().expect("stack underflow")
     }
 
     #[inline(always)]
     #[must_use]
-    pub(crate) fn peek(&mut self, depth: usize) -> Value<'gc> {
+    fn peek(&mut self, depth: usize) -> Value<'gc> {
         *self
             .stack
             .get(self.stack.len() - depth - 1)
@@ -383,7 +442,7 @@ impl<'gc> Vm<'gc> {
 
     #[inline(always)]
     #[must_use]
-    pub(crate) fn peek_forced(&mut self, depth: usize) -> StrictValue<'gc> {
+    fn peek_forced(&mut self, depth: usize) -> StrictValue<'gc> {
         self.stack
             .get(self.stack.len() - depth - 1)
             .expect("stack underflow")
@@ -392,7 +451,7 @@ impl<'gc> Vm<'gc> {
     }
 
     #[inline(always)]
-    pub(crate) fn replace(&mut self, depth: usize, val: Value<'gc>) {
+    fn replace(&mut self, depth: usize, val: Value<'gc>) {
         let len = self.stack.len();
         *self
             .stack
@@ -402,7 +461,7 @@ impl<'gc> Vm<'gc> {
 
     #[inline(always)]
     #[cfg_attr(debug_assertions, track_caller)]
-    pub(crate) fn pop_forced(&mut self) -> StrictValue<'gc> {
+    fn pop_forced(&mut self) -> StrictValue<'gc> {
         self.stack
             .pop()
             .expect("stack underflow")
@@ -410,17 +469,45 @@ impl<'gc> Vm<'gc> {
             .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)]
-    pub(crate) fn try_force<T: Forced<'gc>>(
+    fn force_and_retry<T: Forced<'gc>>(
         &mut self,
         reader: &mut BytecodeReader<'_>,
         mc: &Mutation<'gc>,
     ) -> std::ops::ControlFlow<Break, T> {
-        self.try_force_to_pc(reader, mc, reader.inst_start_pc())
+        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)]
-    pub(crate) fn try_force_to_pc<T: Forced<'gc>>(
+    fn force_and_retry_pc<T: Forced<'gc>>(
         &mut self,
         reader: &mut BytecodeReader<'_>,
         mc: &Mutation<'gc>,
@@ -432,7 +519,7 @@ impl<'gc> Vm<'gc> {
 
     #[inline(always)]
     #[allow(unused)]
-    pub(crate) fn force_slot(
+    fn force_slot(
         &mut self,
         depth: usize,
         reader: &mut BytecodeReader<'_>,
@@ -442,7 +529,7 @@ impl<'gc> Vm<'gc> {
     }
 
     #[inline(always)]
-    pub(crate) fn force_slot_to_pc(
+    fn force_slot_to_pc(
         &mut self,
         depth: usize,
         reader: &mut BytecodeReader<'_>,
@@ -454,29 +541,31 @@ impl<'gc> Vm<'gc> {
         };
         let mut state = thunk.borrow_mut(mc);
         match *state {
-            ThunkState::Pending { ip, env, with_env } => {
+            ThunkState::Pending { ip, env } => {
                 *state = ThunkState::Blackhole;
-                drop(state);
                 self.call_stack.push(CallFrame {
                     thunk: Some(thunk),
-                    stack_depth: depth,
                     pc: resume_pc,
                     env: self.env,
-                    with_env: self.with_env,
                 });
                 self.env = env;
-                self.with_env = with_env;
                 reader.set_pc(ip);
                 Step::Break(Break::Force)
             }
             ThunkState::Evaluated(v) => {
-                drop(state);
                 self.replace(depth, v.relax());
                 Step::Continue(())
             }
-            ThunkState::Apply { .. } => todo!("force apply"),
+            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 => {
-                drop(state);
                 self.finish_err(Error::eval_error("infinite recursion encountered"))
             }
         }
@@ -491,20 +580,19 @@ struct ErrorFrame {
 
 #[derive(Collect, Debug)]
 #[collect(no_drop)]
-pub(crate) struct CallFrame<'gc> {
-    pub(crate) pc: usize,
-    pub(crate) stack_depth: usize,
-    pub(crate) thunk: Option<Gc<'gc, Thunk<'gc>>>,
-    pub(crate) env: Gc<'gc, RefLock<Env<'gc>>>,
-    pub(crate) with_env: Option<Gc<'gc, WithEnv<'gc>>>,
+struct CallFrame<'gc> {
+    pc: usize,
+    thunk: Option<Gc<'gc, Thunk<'gc>>>,
+    env: Gc<'gc, RefLock<Env<'gc>>>,
 }
 
-pub(crate) enum Action {
+enum Action {
     Continue { pc: usize },
     Done(Result<fix_common::Value>),
+    LoadFile(PendingLoad),
 }
 
-pub(crate) enum NixNum {
+enum NixNum {
     Int(i64),
     Float(f64),
 }
@@ -534,6 +622,21 @@ impl Vm<'_> {
                         }
                     }
                 }
+                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;
+                }
                 Action::Done(done) => break done,
             }
         }
@@ -565,6 +668,11 @@ impl<'gc> Vm<'gc> {
                 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"),
+                ),
             }
         }
     }
@@ -649,21 +757,18 @@ impl<'gc> Vm<'gc> {
                 Jump => self.op_jump(&mut reader),
 
                 ConcatStrings => self.op_concat_strings(ctx, &mut reader, mc),
-                ResolvePath => self.op_resolve_path(ctx),
+                CoerceToString => self.op_coerce_to_string(&mut reader, mc),
+                ResolvePath => self.op_resolve_path(ctx, &mut reader, mc),
 
-                Assert => self.op_assert(&mut reader),
+                Assert => self.op_assert(ctx, &mut reader, mc),
 
-                PushWith => self.op_push_with(ctx, &mut reader, mc),
-                PopWith => self.op_pop_with(),
                 LookupWith => self.op_lookup_with(ctx, &mut reader, mc),
-                PrepareWith => self.op_prepare_with(),
 
                 LoadBuiltins => self.op_load_builtins(),
                 LoadBuiltin => self.op_load_builtin(&mut reader),
 
-                MkPos => self.op_mk_pos(&mut reader),
                 LoadReplBinding => self.op_load_repl_binding(&mut reader),
-                LoadScopedBinding => self.op_load_scoped_binding(&mut reader),
+                LoadScopedBinding => self.op_load_scoped_binding(ctx, &mut reader),
 
                 Illegal => unreachable!(),
             };
@@ -673,6 +778,13 @@ impl<'gc> Vm<'gc> {
                 Step::Break(Break::Done) => {
                     return Action::Done(self.result.take().expect("Break::Done without result"));
                 }
+                Step::Break(Break::LoadFile) => {
+                    return Action::LoadFile(
+                        self.pending_load
+                            .take()
+                            .expect("Break::LoadFile without pending_load"),
+                    );
+                }
             }
         }
     }

fix-vm/src/primops/attrs.rs

@@ -0,0 +1 @@
+

fix-vm/src/primops/control.rs

@@ -1,131 +1,12 @@
 use fix_builtins::PrimOpPhase;
 use fix_error::Error;
 use gc_arena::{Gc, Mutation, RefLock};
-use num_enum::TryFromPrimitive as _;
 use smallvec::SmallVec;
 
 use crate::value::*;
-use crate::{BytecodeReader, CallFrame, Step, Vm, VmRuntimeCtx, VmRuntimeCtxExt};
+use crate::{BytecodeReader, Step, Vm, VmRuntimeCtx, VmRuntimeCtxExt};
 
 impl<'gc> Vm<'gc> {
-    #[allow(clippy::too_many_lines)]
-    pub(crate) fn op_dispatch_primop(
-        &mut self,
-        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_primitive(phase_disc) else {
-            return self.finish_err(Error::eval_error("invalid primop phase"));
-        };
-        match phase {
-            Abort => self.primop_abort(ctx, reader, mc),
-
-            DeepSeq => self.primop_deep_seq_force_top(reader, mc),
-            DeepSeqPush => self.primop_deep_seq_push(reader, mc),
-            DeepSeqLoop => self.primop_deep_seq_loop(reader, mc),
-            Seq => self.primop_seq(reader, mc),
-
-            FilterForceList => self.primop_filter_force_list(reader, mc),
-            FilterCallPred => self.primop_filter_call_pred(reader, mc),
-            FilterCheck => self.primop_filter_check(reader, mc),
-
-            ForceResultShallow => self.primop_force_result_shallow(ctx, reader, mc),
-            ForceResultShallowPush => self.primop_force_result_shallow_push(ctx, reader, mc),
-            ForceResultShallowLoop => self.primop_force_result_shallow_loop(reader, mc),
-            ForceResultDeepFinish => self.primop_force_result_deep_finish(ctx, reader, mc),
-
-            CallPattern => self.primop_call_pattern(ctx, reader, mc),
-
-            phase => todo!("primop phase {phase:?}"),
-        }
-    }
-
-    fn return_from_primop(&mut self, reader: &mut BytecodeReader<'_>) -> Step {
-        let Some(CallFrame {
-            pc: ret_pc,
-            stack_depth: _,
-            thunk: _,
-            env,
-            with_env,
-        }) = self.call_stack.pop()
-        else {
-            unreachable!()
-        };
-        reader.set_pc(ret_pc);
-        self.call_depth -= 1;
-        self.env = env;
-        self.with_env = with_env;
-        Step::Continue(())
-    }
-
-    pub(crate) fn primop_filter_force_list(
-        &mut self,
-        reader: &mut BytecodeReader<'_>,
-        mc: &Mutation<'gc>,
-    ) -> Step {
-        self.force_slot(0, reader, mc)?;
-        let list = match self.peek_forced(0).expect_gc::<List>() {
-            Ok(list) => list,
-            Err(got) => return self.finish_type_err(NixType::List, got),
-        };
-        if list.inner.borrow().is_empty() {
-            return self.return_from_primop(reader);
-        }
-        // prepare stack layout: [ pred list idx acc ]
-        self.push(Value::new_inline(0));
-        self.push(Value::new_gc(List::new_gc(mc)));
-        reader.set_pc(PrimOpPhase::FilterCallPred.ip() as usize);
-        Step::Continue(())
-    }
-
-    pub(crate) fn primop_filter_call_pred(
-        &mut self,
-        reader: &mut BytecodeReader<'_>,
-        mc: &Mutation<'gc>,
-    ) -> Step {
-        self.force_slot(3, reader, mc)?;
-        let pred = self.peek_forced(3);
-        #[allow(clippy::unwrap_used)]
-        let idx = self.peek(1).as_inline::<i32>().unwrap();
-        #[allow(clippy::unwrap_used)]
-        let elem = self.peek_forced(2).as_gc::<List>().unwrap().inner.borrow()[idx as usize];
-        self.push(pred.relax());
-        self.call(reader, mc, elem, PrimOpPhase::FilterCheck.ip() as usize)
-    }
-
-    pub(crate) fn primop_filter_check(
-        &mut self,
-        reader: &mut BytecodeReader<'_>,
-        mc: &Mutation<'gc>,
-    ) -> Step {
-        let ret = self.try_force::<bool>(reader, mc)?;
-        #[allow(clippy::unwrap_used)]
-        let idx = self.peek(1).as_inline::<i32>().unwrap();
-        #[allow(clippy::unwrap_used)]
-        let list = self.peek_forced(2).as_gc::<List>().unwrap();
-        let list = list.inner.borrow();
-        #[allow(clippy::unwrap_used)]
-        let acc = self.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 = self.pop();
-            let _ = self.pop(); // idx
-            let _ = self.pop(); // list
-            let _ = self.pop(); // pred
-            self.push(acc);
-            return self.return_from_primop(reader);
-        }
-        self.replace(1, Value::new_inline(idx + 1));
-        reader.set_pc(PrimOpPhase::FilterCallPred.ip() as usize);
-        Step::Continue(())
-    }
-
     pub(crate) fn primop_seq(
         &mut self,
         reader: &mut BytecodeReader<'_>,
@@ -135,8 +16,7 @@ impl<'gc> Vm<'gc> {
         self.force_slot(1, reader, mc)?;
         let e2 = self.pop();
         let _ = self.pop();
-        self.push(e2);
-        self.return_from_primop(reader)
+        self.return_from_primop(e2, reader)
     }
 
     pub(crate) fn primop_abort(
@@ -165,7 +45,7 @@ impl<'gc> Vm<'gc> {
         let e1 = self.peek_forced(1);
 
         let children: SmallVec<_> = if let Some(attrs) = e1.as_gc::<AttrSet>() {
-            let attrs = attrs.entries.borrow();
+            let attrs = &attrs.entries;
             if attrs.is_empty() {
                 SmallVec::new()
             } else {
@@ -185,8 +65,7 @@ impl<'gc> Vm<'gc> {
         if children.is_empty() {
             let e2 = self.pop();
             let _ = self.pop();
-            self.push(e2);
-            return self.return_from_primop(reader);
+            return self.return_from_primop(e2, reader);
         }
 
         let count = children.len() as i32;
@@ -215,7 +94,8 @@ impl<'gc> Vm<'gc> {
             let _ = self.pop(); // counter
             let _ = self.pop(); // worklist
             let _ = self.pop(); // seen
-            return self.return_from_primop(reader);
+            let val = self.pop();
+            return self.return_from_primop(val, reader);
         }
 
         #[allow(clippy::unwrap_used)]
@@ -243,7 +123,7 @@ impl<'gc> Vm<'gc> {
 
         let mut added: usize = 0;
         if let Some(attrs) = item.as_gc::<AttrSet>() {
-            let attrs = attrs.entries.borrow();
+            let attrs = &attrs.entries;
             #[allow(clippy::unwrap_used)]
             let seen = self.peek_forced(2).as_gc::<List<'gc>>().unwrap();
             if !self.is_value_in_seen(seen, item) {
@@ -291,7 +171,7 @@ impl<'gc> Vm<'gc> {
         let val = self.peek_forced(0);
 
         let (count, has_children) = if let Some(attrs) = val.as_gc::<AttrSet>() {
-            let len = attrs.entries.borrow().len();
+            let len = attrs.entries.len();
             (len, len > 0)
         } else if let Some(list) = val.as_gc::<List<'gc>>() {
             let len = list.inner.borrow().len();
@@ -331,7 +211,7 @@ impl<'gc> Vm<'gc> {
 
         let val = self.peek_forced(2);
         let child = if let Some(attrs) = val.as_gc::<AttrSet>() {
-            attrs.entries.borrow().get(idx as usize).map(|&(_, v)| v)
+            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 {
@@ -368,17 +248,73 @@ impl<'gc> Vm<'gc> {
         reader: &mut BytecodeReader<'_>,
         mc: &Mutation<'gc>,
     ) -> Step {
-        let val = self.try_force::<StrictValue>(reader, mc)?;
+        let val = self.force_and_retry::<StrictValue>(reader, mc)?;
         self.finish_ok(ctx.convert_value(val.relax()))
     }
 
+    fn is_value_in_seen(&self, 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(&self, seen: Gc<'gc, List<'gc>>, mc: &Mutation<'gc>, val: Value<'gc>) {
+        if is_container(val) {
+            seen.unlock(mc).borrow_mut().push(val);
+        }
+    }
+
+    pub(crate) fn primop_call_functor_1(
+        &mut self,
+        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 = self.force_and_retry::<StrictValue>(reader, mc)?;
+        // Stack now: [..., orig_arg, self]
+        let self_val = self.pop();
+        self.push(functor.relax());
+        // Stack: [..., orig_arg, functor]
+        // Call 1: functor(self). Resume into CallFunctor2 once it returns.
+        self.call(
+            reader,
+            mc,
+            self_val,
+            PrimOpPhase::CallFunctor2.ip() as usize,
+        )
+    }
+
+    pub(crate) fn primop_call_functor_2(
+        &mut self,
+        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 = self.pop();
+        let orig_arg = self.pop();
+        let saved = self.call_stack.pop().expect("functor outer frame missing");
+        self.env = saved.env;
+        self.push(intermediate);
+        // Call 2: intermediate(orig_arg). Resume to caller.
+        self.call(reader, mc, orig_arg, saved.pc)
+    }
+
     pub(crate) fn primop_call_pattern(
         &mut self,
         ctx: &mut impl VmRuntimeCtx,
         reader: &mut BytecodeReader<'_>,
         mc: &Mutation<'gc>,
     ) -> Step {
-        let (func, attrset) = self.try_force::<(Gc<Closure>, Gc<AttrSet>)>(reader, mc)?;
+        let (func, attrset) = self.force_and_retry::<(Gc<Closure>, Gc<AttrSet>)>(reader, mc)?;
 
         let Closure {
             ip,
@@ -400,7 +336,7 @@ impl<'gc> Vm<'gc> {
                     )));
                 }
             }
-            for &(key, _) in attrset.entries.borrow().iter() {
+            for &(key, _) in attrset.entries.iter() {
                 let is_expected =
                     pattern.required.contains(&key) || pattern.optional.contains(&key);
                 if !is_expected {
@@ -421,25 +357,6 @@ impl<'gc> Vm<'gc> {
 
         Step::Continue(())
     }
-
-    fn is_value_in_seen(&self, 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(&self, seen: Gc<'gc, List<'gc>>, mc: &Mutation<'gc>, val: Value<'gc>) {
-        if is_container(val) {
-            seen.unlock(mc).borrow_mut().push(val);
-        }
-    }
 }
 
 fn is_container(val: Value<'_>) -> bool {

fix-vm/src/primops/conv.rs

@@ -0,0 +1 @@
+

fix-vm/src/primops/io.rs

@@ -0,0 +1,169 @@
+use std::path::PathBuf;
+
+use fix_builtins::PrimOpPhase;
+use fix_common::StringId;
+use fix_error::Error;
+use gc_arena::{Gc, Mutation};
+use hashbrown::HashSet;
+
+use crate::bytecode_reader::BytecodeReader;
+use crate::value::*;
+use crate::{Break, CallFrame, PendingLoad, PendingScope, Step, Vm, VmRuntimeCtx, VmRuntimeCtxExt};
+
+impl<'gc> Vm<'gc> {
+    pub(crate) fn primop_import(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        // stack: [path]
+        let path_val = self.force_and_retry::<StrictValue>(reader, mc)?;
+        let path_str = match ctx.get_string(path_val) {
+            Some(s) => s.to_owned(),
+            None => {
+                return self.finish_err(Error::eval_error(format!(
+                    "expected a path string, got {}",
+                    path_val.ty()
+                )));
+            }
+        };
+        let abs = match resolve_import_target(&path_str) {
+            Ok(p) => p,
+            Err(e) => return self.finish_err(e),
+        };
+
+        if let Some(&cached) = self.import_cache.get(&abs) {
+            return self.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());
+        self.push(Value::new_inline(path_sid));
+        self.call_stack.push(CallFrame {
+            pc: PrimOpPhase::ImportFinalize.ip() as usize,
+            thunk: None,
+            env: self.env,
+        });
+
+        self.pending_load = Some(PendingLoad {
+            path: abs,
+            scope: None,
+        });
+        Step::Break(Break::LoadFile)
+    }
+
+    pub(crate) fn primop_import_finalize(
+        &mut self,
+        _ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        _mc: &Mutation<'gc>,
+    ) -> Step {
+        // stack: [path_sid, return_value]
+        let val = self.pop();
+        #[allow(clippy::unwrap_used)]
+        let path_sid = self.pop().as_inline::<StringId>().unwrap();
+        // The cache key is keyed by the absolute path string we interned in
+        // `primop_import`. Resolve it back to the host PathBuf.
+        let path_str = _ctx.resolve_string(path_sid).to_owned();
+        self.import_cache.insert(PathBuf::from(path_str), val);
+        self.return_from_primop(val, reader)
+    }
+
+    pub(crate) fn primop_scoped_import(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        // stack: [scope, path]
+        let (scope_attrs, path_val) =
+            self.force_and_retry::<(Gc<AttrSet>, StrictValue)>(reader, mc)?;
+        let path_str = match ctx.get_string(path_val) {
+            Some(s) => s.to_owned(),
+            None => {
+                return self.finish_err(Error::eval_error(format!(
+                    "expected a path string, got {}",
+                    path_val.ty()
+                )));
+            }
+        };
+        let abs = match resolve_import_target(&path_str) {
+            Ok(p) => p,
+            Err(e) => return self.finish_err(e),
+        };
+
+        let keys: HashSet<StringId> = scope_attrs.entries.iter().map(|&(k, _)| k).collect();
+        let slot_id = self.scope_slots.len() as u32;
+        self.scope_slots.push(Value::new_gc(scope_attrs));
+
+        self.call_stack.push(CallFrame {
+            pc: PrimOpPhase::ScopedImportFinalize.ip() as usize,
+            thunk: None,
+            env: self.env,
+        });
+
+        self.pending_load = Some(PendingLoad {
+            path: abs,
+            scope: Some(PendingScope { keys, slot_id }),
+        });
+        Step::Break(Break::LoadFile)
+    }
+
+    pub(crate) fn primop_scoped_import_finalize(
+        &mut self,
+        _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 = self.pop();
+        self.return_from_primop(val, reader)
+    }
+
+    pub(crate) fn primop_path_exists(
+        &mut self,
+        ctx: &mut impl VmRuntimeCtx,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let path_val = self.force_and_retry::<StrictValue>(reader, mc)?;
+        let path = match ctx.get_string(path_val) {
+            Some(s) => s.to_owned(),
+            None => {
+                return self.finish_err(Error::eval_error(format!(
+                    "expected a path string, got {}",
+                    path_val.ty()
+                )));
+            }
+        };
+        let must_be_dir = path.ends_with('/') || path.ends_with("/.");
+        let p = std::path::Path::new(&path);
+        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()
+        };
+        self.return_from_primop(Value::new_inline(exists), reader)
+    }
+}
+
+/// Convert the user-supplied path string into an absolute, dotted-segment
+/// resolved `PathBuf` and append `default.nix` if the target is a directory.
+fn resolve_import_target(path: &str) -> Result<PathBuf, Box<Error>> {
+    let mut abs = PathBuf::from(path);
+    if !abs.is_absolute() {
+        return Err(Error::eval_error(format!(
+            "import: expected an absolute path, got '{path}'"
+        )));
+    }
+    if abs.is_dir() {
+        abs.push("default.nix");
+    }
+    Ok(abs)
+}

fix-vm/src/primops/list.rs

@@ -0,0 +1,73 @@
+use fix_builtins::PrimOpPhase;
+use gc_arena::Mutation;
+
+use crate::bytecode_reader::BytecodeReader;
+use crate::value::*;
+use crate::{Step, Vm};
+
+impl<'gc> Vm<'gc> {
+    pub(crate) fn primop_filter_force_list(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        self.force_slot(0, reader, mc)?;
+        let list = match self.peek_forced(0).expect_gc::<List>() {
+            Ok(list) => list,
+            Err(got) => return self.finish_type_err(NixType::List, got),
+        };
+        if list.inner.borrow().is_empty() {
+            let val = self.pop();
+            return self.return_from_primop(val, reader);
+        }
+        // prepare stack layout: [ pred list idx acc ]
+        self.push(Value::new_inline(0));
+        self.push(Value::new_gc(List::new_gc(mc)));
+        reader.set_pc(PrimOpPhase::FilterCallPred.ip() as usize);
+        Step::Continue(())
+    }
+
+    pub(crate) fn primop_filter_call_pred(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        self.force_slot(3, reader, mc)?;
+        let pred = self.peek_forced(3);
+        #[allow(clippy::unwrap_used)]
+        let idx = self.peek(1).as_inline::<i32>().unwrap();
+        #[allow(clippy::unwrap_used)]
+        let elem = self.peek_forced(2).as_gc::<List>().unwrap().inner.borrow()[idx as usize];
+        self.push(pred.relax());
+        self.call(reader, mc, elem, PrimOpPhase::FilterCheck.ip() as usize)
+    }
+
+    pub(crate) fn primop_filter_check(
+        &mut self,
+        reader: &mut BytecodeReader<'_>,
+        mc: &Mutation<'gc>,
+    ) -> Step {
+        let ret = self.force_and_retry::<bool>(reader, mc)?;
+        #[allow(clippy::unwrap_used)]
+        let idx = self.peek(1).as_inline::<i32>().unwrap();
+        #[allow(clippy::unwrap_used)]
+        let list = self.peek_forced(2).as_gc::<List>().unwrap();
+        let list = list.inner.borrow();
+        #[allow(clippy::unwrap_used)]
+        let acc = self.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 = self.pop();
+            let _ = self.pop(); // idx
+            let _ = self.pop(); // list
+            let _ = self.pop(); // pred
+            return self.return_from_primop(acc, reader);
+        }
+        self.replace(1, Value::new_inline(idx + 1));
+        reader.set_pc(PrimOpPhase::FilterCallPred.ip() as usize);
+        Step::Continue(())
+    }
+}

fix-vm/src/primops/mod.rs

@@ -0,0 +1,79 @@
+use fix_builtins::PrimOpPhase;
+use fix_error::Error;
+use gc_arena::Mutation;
+use num_enum::TryFromPrimitive;
+
+use crate::bytecode_reader::BytecodeReader;
+use crate::value::Value;
+use crate::{CallFrame, Step, Vm, VmRuntimeCtx};
+
+mod attrs;
+mod control;
+mod conv;
+mod io;
+mod list;
+mod path;
+mod regex;
+mod version;
+
+impl<'gc> Vm<'gc> {
+    #[allow(clippy::too_many_lines)]
+    pub(crate) fn op_dispatch_primop(
+        &mut self,
+        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_primitive(phase_disc) else {
+            return self.finish_err(Error::eval_error("invalid primop phase"));
+        };
+        match phase {
+            Abort => self.primop_abort(ctx, reader, mc),
+
+            DeepSeq => self.primop_deep_seq_force_top(reader, mc),
+            DeepSeqPush => self.primop_deep_seq_push(reader, mc),
+            DeepSeqLoop => self.primop_deep_seq_loop(reader, mc),
+            Seq => self.primop_seq(reader, mc),
+
+            FilterForceList => self.primop_filter_force_list(reader, mc),
+            FilterCallPred => self.primop_filter_call_pred(reader, mc),
+            FilterCheck => self.primop_filter_check(reader, mc),
+
+            ForceResultShallow => self.primop_force_result_shallow(ctx, reader, mc),
+            ForceResultShallowPush => self.primop_force_result_shallow_push(ctx, reader, mc),
+            ForceResultShallowLoop => self.primop_force_result_shallow_loop(reader, mc),
+            ForceResultDeepFinish => self.primop_force_result_deep_finish(ctx, reader, mc),
+
+            CallPattern => self.primop_call_pattern(ctx, reader, mc),
+            CallFunctor1 => self.primop_call_functor_1(reader, mc),
+            CallFunctor2 => self.primop_call_functor_2(reader, mc),
+
+            Import => self.primop_import(ctx, reader, mc),
+            ImportFinalize => self.primop_import_finalize(ctx, reader, mc),
+            ScopedImport => self.primop_scoped_import(ctx, reader, mc),
+            ScopedImportFinalize => self.primop_scoped_import_finalize(ctx, reader, mc),
+
+            PathExists => self.primop_path_exists(ctx, reader, mc),
+
+            phase => todo!("primop phase {phase:?}"),
+        }
+    }
+
+    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.call_stack.pop()
+        else {
+            unreachable!()
+        };
+        reader.set_pc(ret_pc);
+        self.call_depth -= 1;
+        self.env = env;
+        Step::Continue(())
+    }
+}

fix-vm/src/primops/path.rs

@@ -0,0 +1 @@
+

fix-vm/src/primops/regex.rs

@@ -0,0 +1 @@
+

fix-vm/src/primops/version.rs

@@ -0,0 +1 @@
+

fix-vm/src/value.rs

@@ -435,78 +435,58 @@ impl fmt::Debug for NixString {
 #[derive(Collect, Debug, Default)]
 #[collect(no_drop)]
 pub(crate) struct AttrSet<'gc> {
-    pub(crate) entries: RefLock<SmallVec<[(StringId, Value<'gc>); 4]>>,
-}
-
-impl<'gc> Unlock for AttrSet<'gc> {
-    type Unlocked = RefCell<SmallVec<[(StringId, Value<'gc>); 4]>>;
-    unsafe fn unlock_unchecked(&self) -> &Self::Unlocked {
-        unsafe { self.entries.unlock_unchecked() }
-    }
+    pub(crate) entries: SmallVec<[(StringId, Value<'gc>); 4]>,
 }
 
 impl<'gc> AttrSet<'gc> {
     pub(crate) fn from_sorted_unchecked(entries: SmallVec<[(StringId, Value<'gc>); 4]>) -> Self {
         debug_assert!(entries.is_sorted_by_key(|(key, _)| *key));
-        Self {
-            entries: RefLock::new(entries),
-        }
+        Self { entries }
     }
 
     pub(crate) fn lookup(&self, key: StringId) -> Option<Value<'gc>> {
-        let entries = self.entries.borrow();
-        entries
+        self.entries
             .binary_search_by_key(&key, |(k, _)| *k)
             .ok()
-            .map(|i| entries[i].1)
+            .map(|i| self.entries[i].1)
     }
 
     pub(crate) fn has(&self, key: StringId) -> bool {
-        self.entries
-            .borrow()
-            .binary_search_by_key(&key, |(k, _)| *k)
-            .is_ok()
+        self.entries.binary_search_by_key(&key, |(k, _)| *k).is_ok()
     }
 
     pub(crate) fn merge(&self, other: &Self, mc: &Mutation<'gc>) -> Gc<'gc, Self> {
         use std::cmp::Ordering::*;
 
-        let self_entries = self.entries.borrow();
-        let other_entries = other.entries.borrow();
-        debug_assert!(self_entries.is_sorted_by_key(|(key, _)| *key));
-        debug_assert!(other_entries.is_sorted_by_key(|(key, _)| *key));
+        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) {
+        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]);
+                    entries.push(self.entries[i]);
                     i += 1;
                 }
                 Greater => {
-                    entries.push(other_entries[j]);
+                    entries.push(other.entries[j]);
                     j += 1;
                 }
                 Equal => {
-                    entries.push(other_entries[j]);
+                    entries.push(other.entries[j]);
                     i += 1;
                     j += 1;
                 }
             }
         }
-        entries.extend(other_entries[j..].iter().cloned());
-        entries.extend(self_entries[i..].iter().cloned());
+        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: RefLock::new(entries),
-            },
-        )
+        Gc::new(mc, AttrSet { entries })
     }
 }
 
@@ -544,15 +524,8 @@ pub(crate) type Thunk<'gc> = RefLock<ThunkState<'gc>>;
 #[derive(Collect, Debug)]
 #[collect(no_drop)]
 pub(crate) enum ThunkState<'gc> {
-    Pending {
-        ip: usize,
-        env: GcEnv<'gc>,
-        with_env: Option<GcWithEnv<'gc>>,
-    },
-    Apply {
-        func: Value<'gc>,
-        arg: Value<'gc>,
-    },
+    Pending { ip: usize, env: GcEnv<'gc> },
+    Apply { func: Value<'gc>, arg: Value<'gc> },
     Blackhole,
     Evaluated(StrictValue<'gc>),
 }

fix/src/lib.rs

@@ -8,7 +8,10 @@ use fix_codegen::{BytecodeContext, InstructionPtr, Op};
 use fix_common::{StringId, Symbol};
 use fix_error::{Error, Result, Source};
 use fix_ir::downgrade::{Downgrade as _, DowngradeContext};
-use fix_ir::{Ir, IrRef, MaybeThunk, RawIrRef, ThunkId};
+use fix_ir::{
+    GhostMaybeThunkRef, GhostRoIrRef, GhostRoMaybeThunkRef, GhostRoRef, Ir, MaybeThunk, RawIrRef,
+    ThunkId,
+};
 use fix_vm::{ForceMode, StaticValue, Vm, VmCode, VmContext, VmRuntimeCtx};
 use ghost_cell::{GhostCell, GhostToken};
 use hashbrown::{HashMap, HashSet};
@@ -30,7 +33,10 @@ pub struct CodeState {
     pub sources: Vec<Source>,
     pub spans: Vec<(usize, rnix::TextRange)>,
     pub thunk_count: usize,
-    pub global_env: HashMap<StringId, Ir<'static, RawIrRef<'static>>>,
+    pub global_env: HashMap<StringId, MaybeThunk>,
+    /// Set during a compilation pass when the code is being compiled under a
+    /// `scopedImport` scope. Read by [`CompilerCtx::current_scope_slot`].
+    pub current_scope_slot: Option<u32>,
 }
 
 pub struct Evaluator {
@@ -64,6 +70,7 @@ impl Evaluator {
                 thunk_count: 0,
                 bytecode,
                 global_env,
+                current_scope_slot: None,
             },
         }
     }
@@ -85,13 +92,13 @@ impl Evaluator {
         source: Source,
         scope: &HashSet<StringId>,
     ) -> Result<fix_common::Value> {
-        self.do_eval(source, Some(Scope::Repl(scope)), ForceMode::Shallow)
+        self.do_eval(source, Some(ExtraScope::Repl(scope)), ForceMode::Shallow)
     }
 
     fn do_eval<'ctx>(
         &'ctx mut self,
         source: Source,
-        extra_scope: Option<Scope<'ctx>>,
+        extra_scope: Option<ExtraScope<'ctx>>,
         force_mode: ForceMode,
     ) -> Result<fix_common::Value> {
         let ip = {
@@ -110,7 +117,7 @@ impl Evaluator {
         _expr: &str,
         _scope: &mut HashSet<StringId>,
     ) -> Result<fix_common::Value> {
-        todo!()
+        todo!("add_binding")
     }
 
     pub fn compile_bytecode(&mut self, source: Source) -> Result<InstructionPtr> {
@@ -147,16 +154,22 @@ impl VmCode for CodeState {
     fn bytecode(&self) -> &[u8] {
         &self.bytecode
     }
-    fn compile(
+    fn compile_with_scope(
         &mut self,
         source: Source,
+        extra_scope: Option<fix_vm::ExtraScope>,
         runtime: &mut impl VmRuntimeCtx,
     ) -> Result<InstructionPtr> {
         let mut compiler = CompilerCtx {
             code: self,
             runtime,
         };
-        compiler.compile_bytecode(source, None)
+        let extra = extra_scope.map(|s| match s {
+            fix_vm::ExtraScope::ScopedImport { keys, slot_id } => {
+                ExtraScope::ScopedImport { keys, slot_id }
+            }
+        });
+        compiler.compile_bytecode(source, extra)
     }
 }
 
@@ -175,14 +188,23 @@ impl<'a, R: VmRuntimeCtx> CompilerCtx<'a, R> {
     fn compile_bytecode(
         &mut self,
         source: Source,
-        extra_scope: Option<Scope>,
+        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<Scope>) -> Result<OwnedIr> {
+    fn downgrade(&mut self, source: Source, extra_scope: Option<ExtraScope>) -> Result<OwnedIr> {
         tracing::debug!("Parsing Nix expression");
 
         self.code.sources.push(source.clone());
@@ -202,7 +224,7 @@ impl<'a, R: VmRuntimeCtx> CompilerCtx<'a, R> {
                 token,
                 self.runtime,
                 &self.code.global_env,
-                extra_scope,
+                extra_scope.map(Into::into),
                 &mut self.code.thunk_count,
                 source,
             );
@@ -245,6 +267,7 @@ impl<'a, R: VmRuntimeCtx> BytecodeContext for CompilerCtx<'a, R> {
             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,
@@ -254,6 +277,22 @@ impl<'a, R: VmRuntimeCtx> BytecodeContext for CompilerCtx<'a, R> {
         };
         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)]
@@ -310,34 +349,20 @@ struct DowngradeCtx<'ctx, 'id, 'ir, R: VmRuntimeCtx> {
     token: GhostToken<'id>,
     runtime: &'ctx mut R,
     source: Source,
-    scopes: Vec<Scope<'ctx>>,
-    with_scope_count: u32,
+    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>>,
 }
 
-fn should_thunk<'id>(ir: IrRef<'id, '_>, token: &GhostToken<'id>) -> bool {
-    !matches!(
-        ir.borrow(token),
-        Ir::Builtin(_)
-            | Ir::Builtins
-            | Ir::Int(_)
-            | Ir::Float(_)
-            | Ir::Bool(_)
-            | Ir::Null
-            | Ir::Str(_)
-            | Ir::Thunk(_)
-    )
-}
-
 impl<'ctx, 'id, 'ir, R: VmRuntimeCtx> DowngradeCtx<'ctx, 'id, 'ir, R> {
     fn new(
         bump: &'ir Bump,
         token: GhostToken<'id>,
         runtime: &'ctx mut R,
-        global: &'ctx HashMap<StringId, Ir<'static, RawIrRef<'static>>>,
-        extra_scope: Option<Scope<'ctx>>,
+        global: &'ctx HashMap<StringId, MaybeThunk>,
+        extra_scope: Option<Scope<'ctx, 'id, 'ir>>,
         thunk_count: &'ctx mut usize,
         source: Source,
     ) -> Self {
@@ -351,7 +376,7 @@ impl<'ctx, 'id, 'ir, R: VmRuntimeCtx> DowngradeCtx<'ctx, 'id, 'ir, R> {
                 .collect(),
             thunk_count,
             arg_count: 0,
-            with_scope_count: 0,
+            with_stack: Vec::new(),
             thunk_scopes: vec![ThunkScope::new_in(bump)],
         }
     }
@@ -360,31 +385,37 @@ impl<'ctx, 'id, 'ir, R: VmRuntimeCtx> DowngradeCtx<'ctx, 'id, 'ir, R> {
 impl<'ctx: 'ir, 'id, 'ir, R: VmRuntimeCtx> DowngradeContext<'id, 'ir>
     for DowngradeCtx<'ctx, 'id, 'ir, R>
 {
-    fn new_expr(&self, expr: Ir<'ir, IrRef<'id, 'ir>>) -> IrRef<'id, 'ir> {
-        IrRef::new(self.bump.alloc(GhostCell::new(expr)))
+    fn new_expr(&self, expr: Ir<'ir, GhostRoRef<'id, 'ir>>) -> GhostRoIrRef<'id, 'ir> {
+        self.bump.alloc(GhostCell::new(expr).into())
     }
 
-    fn maybe_thunk(&mut self, ir: IrRef<'id, 'ir>) -> MaybeThunk {
+    fn maybe_thunk(&mut self, ir: GhostRoIrRef<'id, 'ir>) -> GhostRoMaybeThunkRef<'id, 'ir> {
         use MaybeThunk::*;
-        match *ir.borrow(&self.token) {
-            Ir::Builtin(x) => return Builtin(x),
-            Ir::Int(x) => return Int(x),
-            Ir::Float(x) => return Float(x),
-            Ir::Bool(x) => return Bool(x),
-            Ir::Str(x) => return Str(x),
-            Ir::Thunk(x) => return Thunk(x),
-            Ir::Arg { layer } => return Arg { layer },
-            Ir::Builtins => return Builtins,
-            Ir::Null => return Null,
-            _ => (),
+        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.token);
-        Thunk(id)
+            .add_binding(id, ir);
+        self.bump.alloc(GhostCell::new(Thunk(id)).into())
     }
 
     fn intern_string(&mut self, sym: impl AsRef<str>) -> StringId {
@@ -395,35 +426,35 @@ impl<'ctx: 'ir, 'id, 'ir, R: VmRuntimeCtx> DowngradeContext<'id, 'ir>
         self.runtime.resolve_string(id).into()
     }
 
-    fn lookup(&self, sym: StringId, span: rnix::TextRange) -> Result<MaybeThunk> {
+    fn lookup(
+        &mut self,
+        sym: StringId,
+        span: rnix::TextRange,
+    ) -> Result<GhostRoMaybeThunkRef<'id, 'ir>> {
         for scope in self.scopes.iter().rev() {
             match scope {
                 &Scope::Global(global_scope) => {
-                    use MaybeThunk::*;
                     if let Some(expr) = global_scope.get(&sym) {
-                        let val = match expr {
-                            Ir::Builtins => Builtins,
-                            Ir::Builtin(s) => Builtin(*s),
-                            Ir::Bool(b) => Bool(*b),
-                            Ir::Null => Null,
-                            _ => unreachable!("globals should only contain leaf IR nodes"),
-                        };
-                        return Ok(val);
+                        return Ok(expr.into());
                     }
                 }
                 &Scope::Repl(repl_bindings) => {
                     if repl_bindings.contains(&sym) {
-                        return Ok(MaybeThunk::ReplBinding(sym));
+                        return Ok(self
+                            .bump
+                            .alloc(GhostCell::new(MaybeThunk::ReplBinding(sym)).into()));
                     }
                 }
-                Scope::ScopedImport(scoped_bindings) => {
-                    if scoped_bindings.contains(&sym) {
-                        return Ok(MaybeThunk::ScopedImportBinding(sym));
+                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(MaybeThunk::Thunk(expr));
+                        return Ok(expr.into());
                     }
                 }
                 &Scope::Param {
@@ -431,16 +462,33 @@ impl<'ctx: 'ir, 'id, 'ir, R: VmRuntimeCtx> DowngradeContext<'id, 'ir>
                     abs_layer,
                 } => {
                     if param_sym == sym {
-                        return Ok(MaybeThunk::Arg {
-                            layer: self.thunk_scopes.len() - abs_layer,
-                        });
+                        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_scope_count > 0 {
-            Ok(MaybeThunk::WithLookup(sym))
+        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)),
@@ -456,25 +504,40 @@ impl<'ctx: 'ir, 'id, 'ir, R: VmRuntimeCtx> DowngradeContext<'id, 'ir>
 
     fn with_let_scope<F, Ret>(&mut self, keys: &[StringId], f: F) -> Result<Ret>
     where
-        F: FnOnce(&mut Self) -> Result<(bumpalo::collections::Vec<'ir, IrRef<'id, 'ir>>, Ret)>,
+        F: FnOnce(
+            &mut Self,
+        ) -> Result<(
+            bumpalo::collections::Vec<'ir, GhostRoMaybeThunkRef<'id, 'ir>>,
+            Ret,
+        )>,
     {
         let base = *self.thunk_count;
         *self.thunk_count = self
             .thunk_count
             .checked_add(keys.len())
             .expect("thunk id overflow");
-        let iter = keys
-            .iter()
-            .enumerate()
-            .map(|(offset, &key)| (key, ThunkId(base + offset)));
-        self.scopes.push(Scope::Let(iter.collect()));
-        let (vals, ret) = {
-            let mut guard = ScopeGuard { ctx: self };
-            f(guard.as_ctx())?
-        };
+        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");
-        scope.extend_bindings((base..base + keys.len()).map(ThunkId).zip(vals));
+        for (i, (val, handle)) in vals.into_iter().zip(handles).enumerate() {
+            let thunk = *val.borrow(&self.token);
+            *handle.borrow_mut(&mut self.token) = thunk;
+            let id = ThunkId(base + i);
+            let ir_ref = self
+                .bump
+                .alloc(GhostCell::new(Ir::MaybeThunk(handle.into())).into());
+            scope.add_binding(id, ir_ref);
+        }
         Ok(ret)
     }
 
@@ -484,19 +547,19 @@ impl<'ctx: 'ir, 'id, 'ir, R: VmRuntimeCtx> DowngradeContext<'id, 'ir>
     {
         self.scopes.push(Scope::Param {
             sym,
-            abs_layer: self.thunk_scopes.len(),
+            abs_layer: self.thunk_scopes.len().try_into().expect("scope too deep!"),
         });
         let mut guard = ScopeGuard { ctx: self };
         f(guard.as_ctx())
     }
 
-    fn with_with_scope<F, Ret>(&mut self, f: F) -> Ret
+    fn with_with_scope<F, Ret>(&mut self, namespace: GhostRoMaybeThunkRef<'id, 'ir>, f: F) -> Ret
     where
         F: FnOnce(&mut Self) -> Ret,
     {
-        self.with_scope_count += 1;
+        self.with_stack.push(namespace);
         let ret = f(self);
-        self.with_scope_count -= 1;
+        self.with_stack.pop();
         ret
     }
 
@@ -505,11 +568,14 @@ impl<'ctx: 'ir, 'id, 'ir, R: VmRuntimeCtx> DowngradeContext<'id, 'ir>
         f: F,
     ) -> (
         Ret,
-        bumpalo::collections::Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>,
+        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);
         (
@@ -534,13 +600,15 @@ impl<'id, 'ir, 'ctx: 'ir, R: VmRuntimeCtx> DowngradeCtx<'ctx, 'id, 'ir, R> {
             .pop()
             .expect("no thunk scope left???")
             .bindings;
-        let ir = IrRef::alloc(self.bump, Ir::TopLevel { body, thunks });
-        Ok(ir.freeze(self.token))
+        Ok(Ir::freeze(
+            self.new_expr(Ir::TopLevel { body, thunks }),
+            self.token,
+        ))
     }
 }
 
 struct ThunkScope<'id, 'ir> {
-    bindings: bumpalo::collections::Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>,
+    bindings: bumpalo::collections::Vec<'ir, (ThunkId, GhostRoIrRef<'id, 'ir>)>,
 }
 
 impl<'id, 'ir> ThunkScope<'id, 'ir> {
@@ -550,21 +618,45 @@ impl<'id, 'ir> ThunkScope<'id, 'ir> {
         }
     }
 
-    fn add_binding(&mut self, id: ThunkId, ir: IrRef<'id, 'ir>, _token: &GhostToken<'id>) {
+    fn add_binding(&mut self, id: ThunkId, ir: GhostRoIrRef<'id, 'ir>) {
         self.bindings.push((id, ir));
     }
 
-    fn extend_bindings(&mut self, iter: impl IntoIterator<Item = (ThunkId, IrRef<'id, 'ir>)>) {
+    fn extend_bindings(
+        &mut self,
+        iter: impl IntoIterator<Item = (ThunkId, GhostRoIrRef<'id, 'ir>)>,
+    ) {
         self.bindings.extend(iter);
     }
 }
 
-enum Scope<'ctx> {
-    Global(&'ctx HashMap<StringId, Ir<'static, RawIrRef<'static>>>),
+enum Scope<'ctx, 'id, 'ir> {
+    Global(&'ctx HashMap<StringId, MaybeThunk>),
     Repl(&'ctx HashSet<StringId>),
-    ScopedImport(HashSet<StringId>),
-    Let(HashMap<StringId, ThunkId>),
-    Param { sym: StringId, abs_layer: usize },
+    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> {
@@ -589,15 +681,31 @@ struct OwnedIr {
 }
 
 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(&self) -> RawIrRef<'_> {
-        self.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) }
     }
 }
 

flake.lock

@@ -31,7 +31,6 @@
           "llm-agents",
           "flake-parts"
         ],
-        "import-tree": "import-tree",
         "nixpkgs": [
           "llm-agents",
           "nixpkgs"
@@ -46,11 +45,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1776192490,
-        "narHash": "sha256-5gYQNEs0/vDkHhg63aHS5g0IwG/8HNvU1Vr00cElofk=",
+        "lastModified": 1777369708,
+        "narHash": "sha256-1xW7cRZNsFNPQD+cE0fwnLVStnDth0HSoASEIFeT7uI=",
         "owner": "nix-community",
         "repo": "bun2nix",
-        "rev": "6ef9f144616eedea90b364bb408ef2e1de7b310a",
+        "rev": "e659e1cc4b8e1b21d0aa85f1c481f9db61ecfa98",
         "type": "github"
       },
       "original": {
@@ -68,11 +67,11 @@
         "rust-analyzer-src": "rust-analyzer-src"
       },
       "locked": {
-        "lastModified": 1777018861,
-        "narHash": "sha256-l+dfxHtTq1jQM53xgYudV8ciECFmJ72PcRAqRS4ys04=",
+        "lastModified": 1777796307,
+        "narHash": "sha256-L7xLjorTwVf2aLu5b0ZZY2D0RFXwD/a/a/fFFDikB2w=",
         "owner": "nix-community",
         "repo": "fenix",
-        "rev": "7b33c6466f781cd699fe250c5b69dc4193da67a7",
+        "rev": "0f9881f2344c0b1c100bd9e774555759b7da6fd5",
         "type": "github"
       },
       "original": {
@@ -84,11 +83,11 @@
     "flake-compat": {
       "flake": false,
       "locked": {
-        "lastModified": 1751685974,
-        "narHash": "sha256-NKw96t+BgHIYzHUjkTK95FqYRVKB8DHpVhefWSz/kTw=",
-        "rev": "549f2762aebeff29a2e5ece7a7dc0f955281a1d1",
+        "lastModified": 1777699697,
+        "narHash": "sha256-Eg9b/rq/ECYwNwEXs5i9wHyhxNI0JrYx2srdI2uZMaQ=",
+        "rev": "382052b74656a369c5408822af3f2501e9b1af81",
         "type": "tarball",
-        "url": "https://git.lix.systems/api/v1/repos/lix-project/flake-compat/archive/549f2762aebeff29a2e5ece7a7dc0f955281a1d1.tar.gz"
+        "url": "https://git.lix.systems/api/v1/repos/lix-project/flake-compat/archive/382052b74656a369c5408822af3f2501e9b1af81.tar.gz"
       },
       "original": {
         "type": "tarball",
@@ -103,11 +102,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1775087534,
-        "narHash": "sha256-91qqW8lhL7TLwgQWijoGBbiD4t7/q75KTi8NxjVmSmA=",
+        "lastModified": 1777678872,
+        "narHash": "sha256-EPIFsulyon7Z1vLQq5Fk64GR8L7cQsT+IPhcsukVbgk=",
         "owner": "hercules-ci",
         "repo": "flake-parts",
-        "rev": "3107b77cd68437b9a76194f0f7f9c55f2329ca5b",
+        "rev": "5250617bffd85403b14dbf43c3870e7f255d2c16",
         "type": "github"
       },
       "original": {
@@ -116,21 +115,6 @@
         "type": "github"
       }
     },
-    "import-tree": {
-      "locked": {
-        "lastModified": 1763762820,
-        "narHash": "sha256-ZvYKbFib3AEwiNMLsejb/CWs/OL/srFQ8AogkebEPF0=",
-        "owner": "vic",
-        "repo": "import-tree",
-        "rev": "3c23749d8013ec6daa1d7255057590e9ca726646",
-        "type": "github"
-      },
-      "original": {
-        "owner": "vic",
-        "repo": "import-tree",
-        "type": "github"
-      }
-    },
     "llm-agents": {
       "inputs": {
         "blueprint": "blueprint",
@@ -143,11 +127,11 @@
         "treefmt-nix": "treefmt-nix"
       },
       "locked": {
-        "lastModified": 1777019177,
-        "narHash": "sha256-YjPvucTsKmGO9QVNz07x7sSsK11PB0jtMniRkTolbq4=",
+        "lastModified": 1777786380,
+        "narHash": "sha256-GGKC1WrEoTafJwIXn+fim6cZ/w1ZWVc+DUYdk2lvPvA=",
         "owner": "numtide",
         "repo": "llm-agents.nix",
-        "rev": "8ff0f2a7fcd176b4547da6879ad549de2bbded41",
+        "rev": "961b1096bc0b2ecc7096e360646cd2f29671c55e",
         "type": "github"
       },
       "original": {
@@ -158,11 +142,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1776548001,
-        "narHash": "sha256-ZSK0NL4a1BwVbbTBoSnWgbJy9HeZFXLYQizjb2DPF24=",
+        "lastModified": 1777578337,
+        "narHash": "sha256-Ad49moKWeXtKBJNy2ebiTQUEgdLyvGmTeykAQ9xM+Z4=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "b12141ef619e0a9c1c84dc8c684040326f27cdcc",
+        "rev": "15f4ee454b1dce334612fa6843b3e05cf546efab",
         "type": "github"
       },
       "original": {
@@ -183,11 +167,11 @@
     "rust-analyzer-src": {
       "flake": false,
       "locked": {
-        "lastModified": 1776800521,
-        "narHash": "sha256-f8YJfwAOsLFpIoqZuX3yF69UvMLrkx7iVzMH1pJU7cM=",
+        "lastModified": 1777768857,
+        "narHash": "sha256-zfekJcaVctfAps1KDHwZpwkvAQn7GObRHh3Gl3xocGI=",
         "owner": "rust-lang",
         "repo": "rust-analyzer",
-        "rev": "8954b66d43225e62c92e8bbcc8500191b5cceb1e",
+        "rev": "1102c0b633599564919e36076d4362d7e68dbddc",
         "type": "github"
       },
       "original": {

flake.nix

@@ -48,6 +48,7 @@
               samply
               tokei
 
+              llm-agents.codex
               llm-agents.claude-code
               llm-agents.opencode
               llm-agents.forge