diff --git a/nix-js/src/codegen.rs b/nix-js/src/codegen.rs
index 13103a3..42505ad 100644
--- a/nix-js/src/codegen.rs
+++ b/nix-js/src/codegen.rs
@@ -2,6 +2,7 @@ use std::fmt::{self, Write as _};
 use std::path::Path;
 
 use crate::ir::*;
+use crate::value::Symbol;
 
 pub(crate) struct CodeBuffer {
     buf: String,
@@ -83,7 +84,7 @@ fn joined<Ctx: CodegenContext, I: Iterator, F: Fn(&Ctx, &mut CodeBuffer, I::Item
 }
 
 macro_rules! code {
-    ($buf:expr, $ctx:expr; $($item:expr),* $(,)?) => {{
+    ($buf:expr, $ctx:expr; $($item:expr)*) => {{
         $(
             ($item).compile($ctx, $buf);
         )*
@@ -99,8 +100,8 @@ macro_rules! code {
         write!($buf, $fmt, $($arg)*).unwrap()
     };
 
-    ($buf:expr, $lit:literal) => {
-        $buf.push_str($lit)
+    ($buf:expr, $fmt:literal) => {
+        write!($buf, $fmt).unwrap()
     };
 }
 
@@ -206,7 +207,7 @@ impl<Ctx: CodegenContext> Compile<Ctx> for rnix::TextRange {
 
 pub(crate) trait CodegenContext {
     fn get_ir(&self, id: ExprId) -> &Ir;
-    fn get_sym(&self, id: SymId) -> &str;
+    fn get_sym(&self, id: SymId) -> Symbol<'_>;
     fn get_current_dir(&self) -> &Path;
     fn get_store_dir(&self) -> &str;
     fn get_current_source_id(&self) -> usize;
@@ -219,6 +220,12 @@ impl<Ctx: CodegenContext> Compile<Ctx> for ExprId {
     }
 }
 
+impl<Ctx: CodegenContext> Compile<Ctx> for Symbol<'_> {
+    fn compile(&self, ctx: &Ctx, buf: &mut CodeBuffer) {
+        quoted(self).compile(ctx, buf);
+    }
+}
+
 impl<Ctx: CodegenContext> Compile<Ctx> for Ir {
     fn compile(&self, ctx: &Ctx, buf: &mut CodeBuffer) {
         match self {
@@ -260,8 +267,8 @@ impl<Ctx: CodegenContext> Compile<Ctx> for Ir {
             }
             &Ir::Builtin(Builtin { inner: name, .. }) => {
                 code!(buf, ctx;
-                    "Nix.builtins[",
-                    quoted(ctx.get_sym(name)),
+                    "Nix.builtins["
+                        ctx.get_sym(name)
                     "]"
                 );
             }
@@ -277,37 +284,37 @@ impl<Ctx: CodegenContext> Compile<Ctx> for Ir {
                 let assertion_span = assertion_ir.span();
 
                 code!(buf, ctx;
-                    "Nix.assert(Nix.withContext(\"while evaluating the condition of the assert statement\",",
-                    assertion_span,
-                    ",()=>(",
-                    assertion_ir,
-                    ")),",
-                    ctx.get_ir(expr),
-                    ",",
-                    quoted(assertion_raw),
-                    ",",
-                    assert_span,
+                    "Nix.assert(Nix.withContext(\"while evaluating the condition of the assert statement\","
+                    assertion_span
+                    ",()=>("
+                    assertion_ir
+                    ")),"
+                    ctx.get_ir(expr)
+                    ","
+                    quoted(assertion_raw)
+                    ","
+                    assert_span
                     ")"
                 );
             }
             Ir::CurPos(cur_pos) => {
                 code!(buf, ctx;
-                    "Nix.mkPos(",
-                    cur_pos.span,
+                    "Nix.mkPos("
+                    cur_pos.span
                     ")"
                 );
             }
             &Ir::ReplBinding(ReplBinding { inner: name, .. }) => {
                 code!(buf, ctx;
                     "Nix.getReplBinding("
-                    quoted(ctx.get_sym(name))
+                    ctx.get_sym(name)
                     ")"
                 );
             }
             &Ir::ScopedImportBinding(ScopedImportBinding { inner: name, .. }) => {
                 code!(buf, ctx;
                     "__scope["
-                    quoted(ctx.get_sym(name))
+                    ctx.get_sym(name)
                     "]"
                 );
             }
@@ -397,22 +404,10 @@ impl<Ctx: CodegenContext> Compile<Ctx> for BinOp {
                 );
             }
             PipeL => {
-                code!(buf, ctx;
-                    "Nix.call(",
-                    rhs,
-                    ",",
-                    lhs,
-                    ")"
-                );
+                code!(buf, ctx; "Nix.call(" rhs "," lhs ")");
             }
             PipeR => {
-                code!(buf, ctx;
-                    "Nix.call(",
-                    lhs,
-                    ",",
-                    rhs,
-                    ")"
-                );
+                code!(buf, ctx; "Nix.call(" lhs "," rhs ")");
             }
         }
     }
@@ -421,20 +416,13 @@ impl<Ctx: CodegenContext> Compile<Ctx> for BinOp {
 impl<Ctx: CodegenContext> Compile<Ctx> for UnOp {
     fn compile(&self, ctx: &Ctx, buf: &mut CodeBuffer) {
         use UnOpKind::*;
+        let rhs = ctx.get_ir(self.rhs);
         match self.kind {
             Neg => {
-                code!(buf, ctx;
-                    "Nix.op.sub(0n,",
-                    ctx.get_ir(self.rhs),
-                    ")"
-                );
+                code!(buf, ctx; "Nix.op.sub(0n," rhs ")");
             }
             Not => {
-                code!(buf, ctx;
-                    "Nix.op.bnot(",
-                    ctx.get_ir(self.rhs),
-                    ")"
-                );
+                code!(buf, ctx; "Nix.op.bnot(" ctx.get_ir(self.rhs) ")");
             }
         }
     }
@@ -454,32 +442,33 @@ impl<Ctx: CodegenContext> Compile<Ctx> for Func {
         {
             code!(buf, "Nix.mkFunction(arg{}=>", id);
             if has_thunks {
-                code!(buf, ctx; "{", &self.thunks, "return ", self.body, "}");
+                code!(buf, ctx; "{" self.thunks "return " self.body "}");
             } else {
-                code!(buf, ctx; "(", self.body, ")");
+                code!(buf, ctx; "(" self.body ")");
             }
             code!(buf, ctx;
                 ",["
                 joined(required.iter(), ",", |ctx: &Ctx, buf, &(sym, _)| {
-                    code!(buf, ctx; quoted(ctx.get_sym(sym)));
+                    code!(buf, ctx; ctx.get_sym(sym));
                 })
                 "],["
                 joined(optional.iter(), ",", |ctx: &Ctx, buf, &(sym, _)| {
-                    code!(buf, ctx; quoted(ctx.get_sym(sym)));
+                    code!(buf, ctx; ctx.get_sym(sym));
                 })
                 "],{"
                 joined(required.iter().chain(optional.iter()), ",", |ctx: &Ctx, buf, &(sym, span)| {
-                    code!(buf, ctx; quoted(ctx.get_sym(sym)), ":", span);
+                    code!(buf, ctx; ctx.get_sym(sym) ":" span);
                 })
                 "},"
+                ellipsis
+                ")"
             );
-            code!(buf, "{})", ellipsis);
         } else {
             code!(buf, "arg{}=>", id);
             if has_thunks {
-                code!(buf, ctx; "{", &self.thunks, "return ", self.body, "}");
+                code!(buf, ctx; "{" self.thunks "return " self.body "}");
             } else {
-                code!(buf, ctx; "(", self.body, ")");
+                code!(buf, ctx; "(" self.body ")");
             }
         }
     }
@@ -488,12 +477,12 @@ impl<Ctx: CodegenContext> Compile<Ctx> for Func {
 impl<Ctx: CodegenContext> Compile<Ctx> for Call {
     fn compile(&self, ctx: &Ctx, buf: &mut CodeBuffer) {
         code!(buf, ctx;
-            "Nix.call(",
-            ctx.get_ir(self.func),
-            ",",
-            ctx.get_ir(self.arg),
-            ",",
-            self.span,
+            "Nix.call("
+                ctx.get_ir(self.func)
+                ","
+                ctx.get_ir(self.arg)
+                ","
+                self.span
             ")"
         );
     }
@@ -527,11 +516,8 @@ impl<Ctx: CodegenContext> Compile<Ctx> for TopLevel {
         if self.thunks.is_empty() {
             ctx.get_ir(self.body).compile(ctx, buf);
         } else {
-            code!(buf, "(()=>{");
-            code!(buf, ctx; &self.thunks);
-            code!(buf, "return ");
-            ctx.get_ir(self.body).compile(ctx, buf);
-            code!(buf, "})()");
+            let body = ctx.get_ir(self.body);
+            code!(buf, ctx; "(()=>{" self.thunks "return " body "})()");
         }
     }
 }
@@ -545,7 +531,7 @@ impl<Ctx: CodegenContext> Compile<Ctx> for Select {
                 ",["
                 joined(self.attrpath.iter(), ",", |ctx: &Ctx, buf, attr| {
                     match attr {
-                        Attr::Str(sym, _) => code!(buf, ctx; quoted(ctx.get_sym(*sym))),
+                        Attr::Str(sym, _) => code!(buf, ctx; ctx.get_sym(*sym)),
                         Attr::Dynamic(expr_id, _) => code!(buf, ctx; ctx.get_ir(*expr_id)),
                     }
                 })
@@ -562,7 +548,7 @@ impl<Ctx: CodegenContext> Compile<Ctx> for Select {
                 ",["
                 joined(self.attrpath.iter(), ",", |ctx: &Ctx, buf, attr| {
                     match attr {
-                        Attr::Str(sym, _) => code!(buf, ctx; quoted(ctx.get_sym(*sym))),
+                        Attr::Str(sym, _) => code!(buf, ctx; ctx.get_sym(*sym)),
                         Attr::Dynamic(expr_id, _) => code!(buf, ctx; ctx.get_ir(*expr_id)),
                     }
                 })
@@ -585,12 +571,12 @@ impl<Ctx: CodegenContext> Compile<Ctx> for AttrSet {
 
                     code!(
                         buf, ctx;
-                        quoted(key) ":Nix.withContext(\"while evaluating the attribute '" escaped(key) "'\"," val.span() ",()=>(" val "))"
+                        key ":Nix.withContext(\"while evaluating the attribute '" escaped(&key) "'\"," val.span() ",()=>(" val "))"
                     );
                 })
                 "},{"
                 joined(self.stcs.iter(), ",", |ctx: &Ctx, buf, (&sym, &(_, span))| {
-                    code!(buf, ctx; quoted(ctx.get_sym(sym)) ":" span);
+                    code!(buf, ctx; ctx.get_sym(sym) ":" span);
                 })
                 "},{dynKeys:["
                 joined(self.dyns.iter(), ",", |ctx: &Ctx, buf, (key, _, _)| {
@@ -619,12 +605,12 @@ impl<Ctx: CodegenContext> Compile<Ctx> for AttrSet {
 
                     code!(
                         buf, ctx;
-                        quoted(key) ":Nix.withContext(\"while evaluating the attribute '" escaped(key) "'\"," val.span() ",()=>(" val "))"
+                        key ":Nix.withContext(\"while evaluating the attribute '" escaped(&key) "'\"," val.span() ",()=>(" val "))"
                     );
                 })
                 "},{"
                 joined(self.stcs.iter(), ",", |ctx: &Ctx, buf, (&sym, &(_, span))| {
-                    code!(buf, ctx; quoted(ctx.get_sym(sym)) ":" span);
+                    code!(buf, ctx; ctx.get_sym(sym) ":" span);
                 })
                 "})"
             );
@@ -674,7 +660,7 @@ impl<Ctx: CodegenContext> Compile<Ctx> for HasAttr {
             ",["
             joined(self.rhs.iter(), ",", |ctx: &Ctx, buf, attr| {
                 match attr {
-                    Attr::Str(sym, _) => code!(buf, ctx; quoted(ctx.get_sym(*sym))),
+                    Attr::Str(sym, _) => code!(buf, ctx; ctx.get_sym(*sym)),
                     Attr::Dynamic(expr_id, _) => code!(buf, ctx; ctx.get_ir(*expr_id)),
                 }
             })
diff --git a/nix-js/src/context.rs b/nix-js/src/context.rs
index e09905c..415b2f4 100644
--- a/nix-js/src/context.rs
+++ b/nix-js/src/context.rs
@@ -7,14 +7,15 @@ use rnix::TextRange;
 use string_interner::DefaultStringInterner;
 
 use crate::codegen::{CodegenContext, compile};
+use crate::downgrade::*;
 use crate::error::{Error, Result, Source};
 use crate::ir::{
-    Arg, ArgId, Bool, Builtin, Downgrade as _, DowngradeContext, ExprId, Ir, Null, ReplBinding,
-    ScopedImportBinding, SymId, Thunk, ToIr as _,
+    Arg, ArgId, Bool, Builtin, ExprId, Ir, Null, ReplBinding, ScopedImportBinding, SymId, Thunk,
+    ToIr as _,
 };
 use crate::runtime::{Runtime, RuntimeContext};
 use crate::store::{Store, StoreBackend, StoreConfig};
-use crate::value::Value;
+use crate::value::{Symbol, Value};
 
 pub struct Context {
     ctx: Ctx,
@@ -54,7 +55,8 @@ impl Context {
         let code = self.ctx.compile(source, Some(Scope::Repl(scope)))?;
 
         tracing::debug!("Executing JavaScript");
-        self.runtime.eval(format!("Nix.forceShallow({})", code), &mut self.ctx)
+        self.runtime
+            .eval(format!("Nix.forceShallow({})", code), &mut self.ctx)
     }
 
     pub fn compile(&mut self, source: Source) -> Result<String> {
@@ -65,7 +67,12 @@ impl Context {
         self.ctx.get_store_dir()
     }
 
-    pub fn add_binding<'a>(&'a mut self, name: &str, expr: &str, scope: &'a mut HashSet<SymId>) -> Result<Value> {
+    pub fn add_binding<'a>(
+        &'a mut self,
+        name: &str,
+        expr: &str,
+        scope: &'a mut HashSet<SymId>,
+    ) -> Result<Value> {
         let source = Source::new_repl(expr.to_string())?;
         let code = self.ctx.compile(source, Some(Scope::Repl(scope)))?;
 
@@ -186,10 +193,7 @@ impl Ctx {
         })
     }
 
-    fn downgrade_ctx<'a>(
-        &'a mut self,
-        extra_scope: Option<Scope<'a>>,
-    ) -> DowngradeCtx<'a> {
+    fn downgrade_ctx<'a>(&'a mut self, extra_scope: Option<Scope<'a>>) -> DowngradeCtx<'a> {
         let global_ref = unsafe { self.global.as_ref() };
         DowngradeCtx::new(self, global_ref, extra_scope)
     }
@@ -236,11 +240,7 @@ impl Ctx {
         Ok(code)
     }
 
-    pub(crate) fn compile_scoped(
-        &mut self,
-        source: Source,
-        scope: Vec<String>,
-    ) -> Result<String> {
+    pub(crate) fn compile_scoped(&mut self, source: Source, scope: Vec<String>) -> Result<String> {
         use crate::codegen::compile_scoped;
 
         tracing::debug!("Parsing Nix expression for scoped import");
@@ -262,7 +262,9 @@ impl Ctx {
         );
 
         #[allow(clippy::unwrap_used)]
-        let root = self.downgrade_ctx(Some(scope)).downgrade(root.tree().expr().unwrap())?;
+        let root = self
+            .downgrade_ctx(Some(scope))
+            .downgrade(root.tree().expr().unwrap())?;
 
         tracing::debug!("Generating JavaScript code for scoped import");
         let code = compile_scoped(self.get_ir(root), self);
@@ -275,8 +277,11 @@ impl CodegenContext for Ctx {
     fn get_ir(&self, id: ExprId) -> &Ir {
         self.irs.get(id.0).expect("ExprId out of bounds")
     }
-    fn get_sym(&self, id: SymId) -> &str {
-        self.symbols.resolve(id).expect("SymId out of bounds")
+    fn get_sym(&self, id: SymId) -> Symbol<'_> {
+        self.symbols
+            .resolve(id)
+            .expect("SymId out of bounds")
+            .into()
     }
     fn get_current_dir(&self) -> &std::path::Path {
         self.get_current_dir()
@@ -420,7 +425,7 @@ impl DowngradeContext for DowngradeCtx<'_> {
         self.ctx.symbols.get_or_intern(sym)
     }
 
-    fn get_sym(&self, id: SymId) -> &str {
+    fn get_sym(&self, id: SymId) -> Symbol<'_> {
         self.ctx.get_sym(id)
     }
 
diff --git a/nix-js/src/ir/utils.rs b/nix-js/src/downgrade.rs
similarity index 62%
rename from nix-js/src/ir/utils.rs
rename to nix-js/src/downgrade.rs
index a149e43..42020d8 100644
--- a/nix-js/src/ir/utils.rs
+++ b/nix-js/src/downgrade.rs
@@ -5,14 +5,488 @@ use hashbrown::hash_map::Entry;
 use hashbrown::{HashMap, HashSet};
 use itertools::Itertools as _;
 use rnix::TextRange;
-use rnix::ast::{self, HasEntry};
+use rnix::ast::{self, AstToken, Expr, HasEntry};
 use rowan::ast::AstNode;
 
-use crate::error::{Error, Result};
-use crate::ir::{Attr, AttrSet, ConcatStrings, ExprId, Select, Str, SymId};
-use crate::value::format_symbol;
+use crate::error::{Error, Result, Source};
+use crate::ir::*;
+use crate::value::Symbol;
 
-use super::*;
+pub trait DowngradeContext {
+    fn downgrade(self, expr: rnix::ast::Expr) -> Result<ExprId>;
+
+    fn new_expr(&mut self, expr: Ir) -> ExprId;
+    fn new_arg(&mut self, span: TextRange) -> ExprId;
+    fn maybe_thunk(&mut self, id: ExprId) -> ExprId;
+
+    fn new_sym(&mut self, sym: String) -> SymId;
+    fn get_sym(&self, id: SymId) -> Symbol<'_>;
+    fn lookup(&mut self, sym: SymId, span: TextRange) -> Result<ExprId>;
+
+    fn get_ir(&self, id: ExprId) -> &Ir;
+    fn replace_ir(&mut self, id: ExprId, expr: Ir);
+    fn reserve_slots(&mut self, slots: usize) -> impl Iterator<Item = ExprId> + Clone + use<Self>;
+    fn get_current_source(&self) -> Source;
+
+    fn with_param_scope<F, R>(&mut self, param: SymId, arg: ExprId, f: F) -> R
+    where
+        F: FnOnce(&mut Self) -> R;
+    fn with_let_scope<F, R>(&mut self, bindings: HashMap<SymId, ExprId>, f: F) -> R
+    where
+        F: FnOnce(&mut Self) -> R;
+    fn with_with_scope<F, R>(&mut self, namespace: ExprId, f: F) -> R
+    where
+        F: FnOnce(&mut Self) -> R;
+
+    fn push_thunk_scope(&mut self);
+    fn pop_thunk_scope(&mut self) -> Vec<(ExprId, ExprId)>;
+    fn register_thunk(&mut self, slot: ExprId, inner: ExprId);
+}
+
+pub trait Downgrade<Ctx: DowngradeContext> {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId>;
+}
+
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for Expr {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        use Expr::*;
+        match self {
+            Apply(apply) => apply.downgrade(ctx),
+            Assert(assert) => assert.downgrade(ctx),
+            Error(error) => {
+                let span = error.syntax().text_range();
+                Err(self::Error::downgrade_error(
+                    error.to_string(),
+                    ctx.get_current_source(),
+                    span,
+                ))
+            }
+            IfElse(ifelse) => ifelse.downgrade(ctx),
+            Select(select) => select.downgrade(ctx),
+            Str(str) => str.downgrade(ctx),
+            Path(path) => path.downgrade(ctx),
+            Literal(lit) => lit.downgrade(ctx),
+            Lambda(lambda) => lambda.downgrade(ctx),
+            LegacyLet(let_) => let_.downgrade(ctx),
+            LetIn(letin) => letin.downgrade(ctx),
+            List(list) => list.downgrade(ctx),
+            BinOp(op) => op.downgrade(ctx),
+            AttrSet(attrs) => attrs.downgrade(ctx),
+            UnaryOp(op) => op.downgrade(ctx),
+            Ident(ident) => ident.downgrade(ctx),
+            With(with) => with.downgrade(ctx),
+            HasAttr(has) => has.downgrade(ctx),
+            Paren(paren) => paren.expr().unwrap().downgrade(ctx),
+            Root(root) => root.expr().unwrap().downgrade(ctx),
+        }
+    }
+}
+
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Assert {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let assertion = self.condition().unwrap();
+        let assertion_raw = assertion.to_string();
+        let assertion = assertion.downgrade(ctx)?;
+        let expr = self.body().unwrap().downgrade(ctx)?;
+        let span = self.syntax().text_range();
+        Ok(ctx.new_expr(
+            Assert {
+                assertion,
+                expr,
+                assertion_raw,
+                span,
+            }
+            .to_ir(),
+        ))
+    }
+}
+
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::IfElse {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let cond = self.condition().unwrap().downgrade(ctx)?;
+        let consq = self.body().unwrap().downgrade(ctx)?;
+        let alter = self.else_body().unwrap().downgrade(ctx)?;
+        let span = self.syntax().text_range();
+        Ok(ctx.new_expr(
+            If {
+                cond,
+                consq,
+                alter,
+                span,
+            }
+            .to_ir(),
+        ))
+    }
+}
+
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Path {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let span = self.syntax().text_range();
+        let parts = self
+            .parts()
+            .map(|part| match part {
+                ast::InterpolPart::Literal(lit) => Ok(ctx.new_expr(
+                    Str {
+                        val: lit.to_string(),
+                        span: lit.syntax().text_range(),
+                    }
+                    .to_ir(),
+                )),
+                ast::InterpolPart::Interpolation(interpol) => {
+                    interpol.expr().unwrap().downgrade(ctx)
+                }
+            })
+            .collect::<Result<Vec<_>>>()?;
+
+        let expr = if parts.len() == 1 {
+            let part = parts.into_iter().next().unwrap();
+            if let &Ir::Str(Str { ref val, span }) = ctx.get_ir(part)
+                && let Some(path) = val.strip_prefix("<").map(|path| &path[..path.len() - 1])
+            {
+                ctx.replace_ir(
+                    part,
+                    Str {
+                        val: path.to_string(),
+                        span,
+                    }
+                    .to_ir(),
+                );
+                let sym = ctx.new_sym("findFile".into());
+                let find_file = ctx.new_expr(Builtin { inner: sym, span }.to_ir());
+                let sym = ctx.new_sym("nixPath".into());
+                let nix_path = ctx.new_expr(Builtin { inner: sym, span }.to_ir());
+                let call = ctx.new_expr(
+                    Call {
+                        func: find_file,
+                        arg: nix_path,
+                        span,
+                    }
+                    .to_ir(),
+                );
+                return Ok(ctx.new_expr(
+                    Call {
+                        func: call,
+                        arg: part,
+                        span,
+                    }
+                    .to_ir(),
+                ));
+            } else {
+                part
+            }
+        } else {
+            ctx.new_expr(
+                ConcatStrings {
+                    parts,
+                    span,
+                    force_string: false,
+                }
+                .to_ir(),
+            )
+        };
+        Ok(ctx.new_expr(Path { expr, span }.to_ir()))
+    }
+}
+
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Str {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let span = self.syntax().text_range();
+        let normalized = self.normalized_parts();
+        let is_single_literal = normalized.len() == 1
+            && matches!(normalized.first(), Some(ast::InterpolPart::Literal(_)));
+
+        let parts = normalized
+            .into_iter()
+            .map(|part| match part {
+                ast::InterpolPart::Literal(lit) => Ok(ctx.new_expr(Str { val: lit, span }.to_ir())),
+                ast::InterpolPart::Interpolation(interpol) => {
+                    let inner = interpol.expr().unwrap().downgrade(ctx)?;
+                    Ok(ctx.maybe_thunk(inner))
+                }
+            })
+            .collect::<Result<Vec<_>>>()?;
+
+        Ok(if is_single_literal {
+            parts.into_iter().next().unwrap()
+        } else {
+            ctx.new_expr(
+                ConcatStrings {
+                    parts,
+                    span,
+                    force_string: true,
+                }
+                .to_ir(),
+            )
+        })
+    }
+}
+
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Literal {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let span = self.syntax().text_range();
+        Ok(ctx.new_expr(match self.kind() {
+            ast::LiteralKind::Integer(int) => Int {
+                inner: int.value().unwrap(),
+                span,
+            }
+            .to_ir(),
+            ast::LiteralKind::Float(float) => Float {
+                inner: float.value().unwrap(),
+                span,
+            }
+            .to_ir(),
+            ast::LiteralKind::Uri(uri) => Str {
+                val: uri.to_string(),
+                span,
+            }
+            .to_ir(),
+        }))
+    }
+}
+
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Ident {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let text = self.ident_token().unwrap().to_string();
+        let span = self.syntax().text_range();
+
+        if text == "__curPos" {
+            return Ok(ctx.new_expr(CurPos { span }.to_ir()));
+        }
+
+        let sym = ctx.new_sym(text);
+        ctx.lookup(sym, span)
+    }
+}
+
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::AttrSet {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let rec = self.rec_token().is_some();
+        let span = self.syntax().text_range();
+
+        if !rec {
+            let attrs = downgrade_attrs(self, ctx)?;
+            return Ok(ctx.new_expr(attrs.to_ir()));
+        }
+
+        // rec { a = 1; b = a; } => let a = 1; b = a; in { inherit a b; }
+        let entries: Vec<_> = self.entries().collect();
+        downgrade_rec_bindings(entries, ctx, span)
+    }
+}
+
+/// Downgrades a list.
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::List {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let items = self
+            .items()
+            .map(|item| {
+                let id = item.downgrade(ctx)?;
+                Ok(ctx.maybe_thunk(id))
+            })
+            .collect::<Result<_>>()?;
+        let span = self.syntax().text_range();
+        Ok(ctx.new_expr(List { items, span }.to_ir()))
+    }
+}
+
+/// Downgrades a binary operation.
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::BinOp {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let lhs = self.lhs().unwrap().downgrade(ctx)?;
+        let rhs = self.rhs().unwrap().downgrade(ctx)?;
+        let kind = self.operator().unwrap().into();
+        let span = self.syntax().text_range();
+        Ok(ctx.new_expr(
+            BinOp {
+                lhs,
+                rhs,
+                kind,
+                span,
+            }
+            .to_ir(),
+        ))
+    }
+}
+
+/// Downgrades a "has attribute" (`?`) expression.
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::HasAttr {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let lhs = self.expr().unwrap().downgrade(ctx)?;
+        let rhs = downgrade_attrpath(self.attrpath().unwrap(), ctx)?;
+        let span = self.syntax().text_range();
+        Ok(ctx.new_expr(HasAttr { lhs, rhs, span }.to_ir()))
+    }
+}
+
+/// Downgrades a unary operation.
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::UnaryOp {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let rhs = self.expr().unwrap().downgrade(ctx)?;
+        let kind = self.operator().unwrap().into();
+        let span = self.syntax().text_range();
+        Ok(ctx.new_expr(UnOp { rhs, kind, span }.to_ir()))
+    }
+}
+
+/// Downgrades an attribute selection (`.`).
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Select {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let expr = self.expr().unwrap().downgrade(ctx)?;
+        let attrpath = downgrade_attrpath(self.attrpath().unwrap(), ctx)?;
+        let default = if let Some(default) = self.default_expr() {
+            let default_expr = default.downgrade(ctx)?;
+            Some(ctx.maybe_thunk(default_expr))
+        } else {
+            None
+        };
+        let span = self.syntax().text_range();
+        Ok(ctx.new_expr(
+            Select {
+                expr,
+                attrpath,
+                default,
+                span,
+            }
+            .to_ir(),
+        ))
+    }
+}
+
+/// Downgrades a `legacy let`, which is essentially a recursive attribute set.
+/// The body of the `let` is accessed via `let.body`.
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::LegacyLet {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let span = self.syntax().text_range();
+        let entries: Vec<_> = self.entries().collect();
+        let attrset_expr = downgrade_let_bindings(entries, ctx, span, |ctx, binding_keys| {
+            // Create plain attrset as body with inherit
+            let mut attrs = AttrSet {
+                stcs: HashMap::new(),
+                dyns: Vec::new(),
+                span,
+            };
+
+            for sym in binding_keys {
+                let expr = ctx.lookup(*sym, rnix::TextRange::default())?;
+                attrs.stcs.insert(*sym, (expr, rnix::TextRange::default()));
+            }
+
+            Ok(ctx.new_expr(attrs.to_ir()))
+        })?;
+
+        let body_sym = ctx.new_sym("body".to_string());
+        let select = Select {
+            expr: attrset_expr,
+            attrpath: vec![Attr::Str(body_sym, rnix::TextRange::default())],
+            default: None,
+            span,
+        };
+
+        Ok(ctx.new_expr(select.to_ir()))
+    }
+}
+
+/// Downgrades a `let ... in ...` expression.
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::LetIn {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let entries: Vec<_> = self.entries().collect();
+        let body_expr = self.body().unwrap();
+        let span = self.syntax().text_range();
+
+        downgrade_let_bindings(entries, ctx, span, |ctx, _binding_keys| {
+            body_expr.downgrade(ctx)
+        })
+    }
+}
+
+/// Downgrades a `with` expression.
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::With {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        // with namespace; expr
+        let namespace = self.namespace().unwrap().downgrade(ctx)?;
+
+        // Downgrade body in With scope
+        let expr = ctx.with_with_scope(namespace, |ctx| self.body().unwrap().downgrade(ctx))?;
+
+        Ok(expr)
+    }
+}
+
+/// Downgrades a lambda (function) expression.
+/// This involves desugaring pattern-matching arguments into `let` bindings.
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Lambda {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let raw_param = self.param().unwrap();
+        let arg = ctx.new_arg(raw_param.syntax().text_range());
+
+        ctx.push_thunk_scope();
+
+        let param;
+        let body;
+
+        match raw_param {
+            ast::Param::IdentParam(id) => {
+                // Simple case: `x: body`
+                let param_sym = ctx.new_sym(id.to_string());
+                param = None;
+
+                // Downgrade body in Param scope
+                body = ctx
+                    .with_param_scope(param_sym, arg, |ctx| self.body().unwrap().downgrade(ctx))?;
+            }
+            ast::Param::Pattern(pattern) => {
+                let alias = pattern
+                    .pat_bind()
+                    .map(|alias| ctx.new_sym(alias.ident().unwrap().to_string()));
+
+                let ellipsis = pattern.ellipsis_token().is_some();
+                let pat_entries = pattern.pat_entries();
+
+                let PatternBindings {
+                    body: inner_body,
+                    required,
+                    optional,
+                } = downgrade_pattern_bindings(pat_entries, alias, arg, ctx, |ctx, _| {
+                    self.body().unwrap().downgrade(ctx)
+                })?;
+
+                param = Some(Param {
+                    required,
+                    optional,
+                    ellipsis,
+                });
+
+                body = inner_body;
+            }
+        }
+
+        let thunks = ctx.pop_thunk_scope();
+        let span = self.syntax().text_range();
+        Ok(ctx.new_expr(
+            Func {
+                body,
+                param,
+                arg,
+                thunks,
+                span,
+            }
+            .to_ir(),
+        ))
+    }
+}
+
+/// Downgrades a function application.
+/// In Nix, function application is left-associative, so `f a b` should be parsed as `((f a) b)`.
+/// Each Apply node represents a single function call with one argument.
+impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Apply {
+    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
+        let func = self.lambda().unwrap().downgrade(ctx)?;
+        let arg = self.argument().unwrap().downgrade(ctx)?;
+        let arg = ctx.maybe_thunk(arg);
+        let span = self.syntax().text_range();
+        Ok(ctx.new_expr(Call { func, arg, span }.to_ir()))
+    }
+}
 
 enum PendingValue {
     Expr(ast::Expr),
@@ -321,10 +795,7 @@ impl PendingAttrSet {
 
             if self.stcs.contains_key(&sym) {
                 return Err(Error::downgrade_error(
-                    format!(
-                        "attribute '{}' already defined",
-                        format_symbol(ctx.get_sym(sym))
-                    ),
+                    format!("attribute '{}' already defined", ctx.get_sym(sym)),
                     ctx.get_current_source(),
                     span,
                 ));
@@ -401,7 +872,7 @@ fn make_attrpath_value_entry(path: Vec<ast::Attr>, value: ast::Expr) -> ast::Ent
 }
 
 /// Downgrades the entries of a non-recursive attribute set.
-pub fn downgrade_attrs(
+fn downgrade_attrs(
     attrs: impl ast::HasEntry + AstNode,
     ctx: &mut impl DowngradeContext,
 ) -> Result<AttrSet> {
@@ -412,7 +883,7 @@ pub fn downgrade_attrs(
 }
 
 /// Downgrades a single attribute key (part of an attribute path).
-pub fn downgrade_attr(attr: ast::Attr, ctx: &mut impl DowngradeContext) -> Result<Attr> {
+fn downgrade_attr(attr: ast::Attr, ctx: &mut impl DowngradeContext) -> Result<Attr> {
     use ast::Attr::*;
     use ast::InterpolPart::*;
     match attr {
@@ -462,7 +933,7 @@ pub fn downgrade_attr(attr: ast::Attr, ctx: &mut impl DowngradeContext) -> Resul
 }
 
 /// Downgrades an attribute path (e.g., `a.b."${c}".d`) into a `Vec<Attr>`.
-pub fn downgrade_attrpath(
+fn downgrade_attrpath(
     attrpath: ast::Attrpath,
     ctx: &mut impl DowngradeContext,
 ) -> Result<Vec<Attr>> {
@@ -472,14 +943,14 @@ pub fn downgrade_attrpath(
         .collect::<Result<Vec<_>>>()
 }
 
-pub struct PatternBindings {
-    pub body: ExprId,
-    pub required: Vec<(SymId, TextRange)>,
-    pub optional: Vec<(SymId, TextRange)>,
+struct PatternBindings {
+    body: ExprId,
+    required: Vec<(SymId, TextRange)>,
+    optional: Vec<(SymId, TextRange)>,
 }
 
 /// Helper function for Lambda pattern parameters.
-pub fn downgrade_pattern_bindings<Ctx>(
+fn downgrade_pattern_bindings<Ctx>(
     pat_entries: impl Iterator<Item = ast::PatEntry>,
     alias: Option<SymId>,
     arg: ExprId,
@@ -507,7 +978,7 @@ where
 
             if !seen_params.insert(sym) {
                 return Err(Error::downgrade_error(
-                    format!("duplicate parameter '{}'", format_symbol(ctx.get_sym(sym))),
+                    format!("duplicate parameter '{}'", ctx.get_sym(sym)),
                     ctx.get_current_source(),
                     span,
                 ));
@@ -603,7 +1074,7 @@ where
 
 /// Downgrades a `let...in` expression. This is a special case of rec attrs
 /// that disallows dynamic attributes and has a body expression.
-pub fn downgrade_let_bindings<Ctx, F>(
+fn downgrade_let_bindings<Ctx, F>(
     entries: Vec<ast::Entry>,
     ctx: &mut Ctx,
     span: TextRange,
@@ -619,7 +1090,7 @@ where
 }
 
 /// Downgrades a `rec` attribute set.
-pub fn downgrade_rec_bindings<Ctx>(
+fn downgrade_rec_bindings<Ctx>(
     entries: Vec<ast::Entry>,
     ctx: &mut Ctx,
     span: TextRange,
@@ -691,7 +1162,7 @@ where
             } else {
                 return Err(Error::internal(format!(
                     "binding '{}' not found",
-                    format_symbol(ctx.get_sym(sym))
+                    ctx.get_sym(sym)
                 )));
             }
         }
@@ -733,10 +1204,7 @@ fn collect_binding_syms<Ctx: DowngradeContext, const ALLOW_DYN: bool>(
     for (sym, (_, span)) in &pending.stcs {
         if !binding_syms.insert(*sym) {
             return Err(Error::downgrade_error(
-                format!(
-                    "attribute '{}' already defined",
-                    format_symbol(ctx.get_sym(*sym))
-                ),
+                format!("attribute '{}' already defined", ctx.get_sym(*sym)),
                 ctx.get_current_source(),
                 *span,
             ));
diff --git a/nix-js/src/ir.rs b/nix-js/src/ir.rs
index 7574a00..30b48cf 100644
--- a/nix-js/src/ir.rs
+++ b/nix-js/src/ir.rs
@@ -3,47 +3,8 @@ use hashbrown::HashMap;
 use rnix::{TextRange, ast};
 use string_interner::symbol::SymbolU32;
 
-use crate::error::{Result, Source};
 use nix_js_macros::ir;
 
-mod downgrade;
-mod utils;
-
-use utils::*;
-
-pub use downgrade::Downgrade;
-
-pub trait DowngradeContext {
-    fn downgrade(self, expr: rnix::ast::Expr) -> Result<ExprId>;
-
-    fn new_expr(&mut self, expr: Ir) -> ExprId;
-    fn new_arg(&mut self, span: TextRange) -> ExprId;
-    fn maybe_thunk(&mut self, id: ExprId) -> ExprId;
-
-    fn new_sym(&mut self, sym: String) -> SymId;
-    fn get_sym(&self, id: SymId) -> &str;
-    fn lookup(&mut self, sym: SymId, span: TextRange) -> Result<ExprId>;
-
-    fn get_ir(&self, id: ExprId) -> &Ir;
-    fn replace_ir(&mut self, id: ExprId, expr: Ir);
-    fn reserve_slots(&mut self, slots: usize) -> impl Iterator<Item = ExprId> + Clone + use<Self>;
-    fn get_current_source(&self) -> Source;
-
-    fn with_param_scope<F, R>(&mut self, param: SymId, arg: ExprId, f: F) -> R
-    where
-        F: FnOnce(&mut Self) -> R;
-    fn with_let_scope<F, R>(&mut self, bindings: HashMap<SymId, ExprId>, f: F) -> R
-    where
-        F: FnOnce(&mut Self) -> R;
-    fn with_with_scope<F, R>(&mut self, namespace: ExprId, f: F) -> R
-    where
-        F: FnOnce(&mut Self) -> R;
-
-    fn push_thunk_scope(&mut self);
-    fn pop_thunk_scope(&mut self) -> Vec<(ExprId, ExprId)>;
-    fn register_thunk(&mut self, slot: ExprId, inner: ExprId);
-}
-
 ir! {
     Ir,
 
diff --git a/nix-js/src/ir/downgrade.rs b/nix-js/src/ir/downgrade.rs
deleted file mode 100644
index 6301305..0000000
--- a/nix-js/src/ir/downgrade.rs
+++ /dev/null
@@ -1,453 +0,0 @@
-// Assume no parse error
-#![allow(clippy::unwrap_used)]
-
-use rnix::ast::{self, AstToken, Expr, HasEntry};
-use rowan::ast::AstNode;
-
-use super::*;
-use crate::error::{Error, Result};
-
-pub trait Downgrade<Ctx: DowngradeContext> {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId>;
-}
-
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for Expr {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        use Expr::*;
-        match self {
-            Apply(apply) => apply.downgrade(ctx),
-            Assert(assert) => assert.downgrade(ctx),
-            Error(error) => {
-                let span = error.syntax().text_range();
-                Err(self::Error::downgrade_error(
-                    error.to_string(),
-                    ctx.get_current_source(),
-                    span,
-                ))
-            }
-            IfElse(ifelse) => ifelse.downgrade(ctx),
-            Select(select) => select.downgrade(ctx),
-            Str(str) => str.downgrade(ctx),
-            Path(path) => path.downgrade(ctx),
-            Literal(lit) => lit.downgrade(ctx),
-            Lambda(lambda) => lambda.downgrade(ctx),
-            LegacyLet(let_) => let_.downgrade(ctx),
-            LetIn(letin) => letin.downgrade(ctx),
-            List(list) => list.downgrade(ctx),
-            BinOp(op) => op.downgrade(ctx),
-            AttrSet(attrs) => attrs.downgrade(ctx),
-            UnaryOp(op) => op.downgrade(ctx),
-            Ident(ident) => ident.downgrade(ctx),
-            With(with) => with.downgrade(ctx),
-            HasAttr(has) => has.downgrade(ctx),
-            Paren(paren) => paren.expr().unwrap().downgrade(ctx),
-            Root(root) => root.expr().unwrap().downgrade(ctx),
-        }
-    }
-}
-
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Assert {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let assertion = self.condition().unwrap();
-        let assertion_raw = assertion.to_string();
-        let assertion = assertion.downgrade(ctx)?;
-        let expr = self.body().unwrap().downgrade(ctx)?;
-        let span = self.syntax().text_range();
-        Ok(ctx.new_expr(
-            Assert {
-                assertion,
-                expr,
-                assertion_raw,
-                span,
-            }
-            .to_ir(),
-        ))
-    }
-}
-
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::IfElse {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let cond = self.condition().unwrap().downgrade(ctx)?;
-        let consq = self.body().unwrap().downgrade(ctx)?;
-        let alter = self.else_body().unwrap().downgrade(ctx)?;
-        let span = self.syntax().text_range();
-        Ok(ctx.new_expr(
-            If {
-                cond,
-                consq,
-                alter,
-                span,
-            }
-            .to_ir(),
-        ))
-    }
-}
-
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Path {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let span = self.syntax().text_range();
-        let parts = self
-            .parts()
-            .map(|part| match part {
-                ast::InterpolPart::Literal(lit) => Ok(ctx.new_expr(
-                    Str {
-                        val: lit.to_string(),
-                        span: lit.syntax().text_range(),
-                    }
-                    .to_ir(),
-                )),
-                ast::InterpolPart::Interpolation(interpol) => {
-                    interpol.expr().unwrap().downgrade(ctx)
-                }
-            })
-            .collect::<Result<Vec<_>>>()?;
-
-        let expr = if parts.len() == 1 {
-            let part = parts.into_iter().next().unwrap();
-            if let &Ir::Str(Str { ref val, span }) = ctx.get_ir(part)
-                && let Some(path) = val.strip_prefix("<").map(|path| &path[..path.len() - 1])
-            {
-                ctx.replace_ir(
-                    part,
-                    Str {
-                        val: path.to_string(),
-                        span,
-                    }
-                    .to_ir(),
-                );
-                let sym = ctx.new_sym("findFile".into());
-                let find_file = ctx.new_expr(Builtin { inner: sym, span }.to_ir());
-                let sym = ctx.new_sym("nixPath".into());
-                let nix_path = ctx.new_expr(Builtin { inner: sym, span }.to_ir());
-                let call = ctx.new_expr(
-                    Call {
-                        func: find_file,
-                        arg: nix_path,
-                        span,
-                    }
-                    .to_ir(),
-                );
-                return Ok(ctx.new_expr(
-                    Call {
-                        func: call,
-                        arg: part,
-                        span,
-                    }
-                    .to_ir(),
-                ));
-            } else {
-                part
-            }
-        } else {
-            ctx.new_expr(
-                ConcatStrings {
-                    parts,
-                    span,
-                    force_string: false,
-                }
-                .to_ir(),
-            )
-        };
-        Ok(ctx.new_expr(Path { expr, span }.to_ir()))
-    }
-}
-
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Str {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let span = self.syntax().text_range();
-        let normalized = self.normalized_parts();
-        let is_single_literal = normalized.len() == 1
-            && matches!(normalized.first(), Some(ast::InterpolPart::Literal(_)));
-
-        let parts = normalized
-            .into_iter()
-            .map(|part| match part {
-                ast::InterpolPart::Literal(lit) => Ok(ctx.new_expr(Str { val: lit, span }.to_ir())),
-                ast::InterpolPart::Interpolation(interpol) => {
-                    let inner = interpol.expr().unwrap().downgrade(ctx)?;
-                    Ok(ctx.maybe_thunk(inner))
-                }
-            })
-            .collect::<Result<Vec<_>>>()?;
-
-        Ok(if is_single_literal {
-            parts.into_iter().next().unwrap()
-        } else {
-            ctx.new_expr(
-                ConcatStrings {
-                    parts,
-                    span,
-                    force_string: true,
-                }
-                .to_ir(),
-            )
-        })
-    }
-}
-
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Literal {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let span = self.syntax().text_range();
-        Ok(ctx.new_expr(match self.kind() {
-            ast::LiteralKind::Integer(int) => Int {
-                inner: int.value().unwrap(),
-                span,
-            }
-            .to_ir(),
-            ast::LiteralKind::Float(float) => Float {
-                inner: float.value().unwrap(),
-                span,
-            }
-            .to_ir(),
-            ast::LiteralKind::Uri(uri) => Str {
-                val: uri.to_string(),
-                span,
-            }
-            .to_ir(),
-        }))
-    }
-}
-
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Ident {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let text = self.ident_token().unwrap().to_string();
-        let span = self.syntax().text_range();
-
-        if text == "__curPos" {
-            return Ok(ctx.new_expr(CurPos { span }.to_ir()));
-        }
-
-        let sym = ctx.new_sym(text);
-        ctx.lookup(sym, span)
-    }
-}
-
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::AttrSet {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let rec = self.rec_token().is_some();
-        let span = self.syntax().text_range();
-
-        if !rec {
-            let attrs = downgrade_attrs(self, ctx)?;
-            return Ok(ctx.new_expr(attrs.to_ir()));
-        }
-
-        // rec { a = 1; b = a; } => let a = 1; b = a; in { inherit a b; }
-        let entries: Vec<_> = self.entries().collect();
-        downgrade_rec_bindings(entries, ctx, span)
-    }
-}
-
-/// Downgrades a list.
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::List {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let items = self
-            .items()
-            .map(|item| {
-                let id = item.downgrade(ctx)?;
-                Ok(ctx.maybe_thunk(id))
-            })
-            .collect::<Result<_>>()?;
-        let span = self.syntax().text_range();
-        Ok(ctx.new_expr(List { items, span }.to_ir()))
-    }
-}
-
-/// Downgrades a binary operation.
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::BinOp {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let lhs = self.lhs().unwrap().downgrade(ctx)?;
-        let rhs = self.rhs().unwrap().downgrade(ctx)?;
-        let kind = self.operator().unwrap().into();
-        let span = self.syntax().text_range();
-        Ok(ctx.new_expr(
-            BinOp {
-                lhs,
-                rhs,
-                kind,
-                span,
-            }
-            .to_ir(),
-        ))
-    }
-}
-
-/// Downgrades a "has attribute" (`?`) expression.
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::HasAttr {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let lhs = self.expr().unwrap().downgrade(ctx)?;
-        let rhs = downgrade_attrpath(self.attrpath().unwrap(), ctx)?;
-        let span = self.syntax().text_range();
-        Ok(ctx.new_expr(HasAttr { lhs, rhs, span }.to_ir()))
-    }
-}
-
-/// Downgrades a unary operation.
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::UnaryOp {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let rhs = self.expr().unwrap().downgrade(ctx)?;
-        let kind = self.operator().unwrap().into();
-        let span = self.syntax().text_range();
-        Ok(ctx.new_expr(UnOp { rhs, kind, span }.to_ir()))
-    }
-}
-
-/// Downgrades an attribute selection (`.`).
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Select {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let expr = self.expr().unwrap().downgrade(ctx)?;
-        let attrpath = downgrade_attrpath(self.attrpath().unwrap(), ctx)?;
-        let default = if let Some(default) = self.default_expr() {
-            let default_expr = default.downgrade(ctx)?;
-            Some(ctx.maybe_thunk(default_expr))
-        } else {
-            None
-        };
-        let span = self.syntax().text_range();
-        Ok(ctx.new_expr(
-            Select {
-                expr,
-                attrpath,
-                default,
-                span,
-            }
-            .to_ir(),
-        ))
-    }
-}
-
-/// Downgrades a `legacy let`, which is essentially a recursive attribute set.
-/// The body of the `let` is accessed via `let.body`.
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::LegacyLet {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let span = self.syntax().text_range();
-        let entries: Vec<_> = self.entries().collect();
-        let attrset_expr = downgrade_let_bindings(entries, ctx, span, |ctx, binding_keys| {
-            // Create plain attrset as body with inherit
-            let mut attrs = AttrSet {
-                stcs: HashMap::new(),
-                dyns: Vec::new(),
-                span,
-            };
-
-            for sym in binding_keys {
-                let expr = ctx.lookup(*sym, rnix::TextRange::default())?;
-                attrs.stcs.insert(*sym, (expr, rnix::TextRange::default()));
-            }
-
-            Ok(ctx.new_expr(attrs.to_ir()))
-        })?;
-
-        let body_sym = ctx.new_sym("body".to_string());
-        let select = Select {
-            expr: attrset_expr,
-            attrpath: vec![Attr::Str(body_sym, rnix::TextRange::default())],
-            default: None,
-            span,
-        };
-
-        Ok(ctx.new_expr(select.to_ir()))
-    }
-}
-
-/// Downgrades a `let ... in ...` expression.
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::LetIn {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let entries: Vec<_> = self.entries().collect();
-        let body_expr = self.body().unwrap();
-        let span = self.syntax().text_range();
-
-        downgrade_let_bindings(entries, ctx, span, |ctx, _binding_keys| {
-            body_expr.downgrade(ctx)
-        })
-    }
-}
-
-/// Downgrades a `with` expression.
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::With {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        // with namespace; expr
-        let namespace = self.namespace().unwrap().downgrade(ctx)?;
-
-        // Downgrade body in With scope
-        let expr = ctx.with_with_scope(namespace, |ctx| self.body().unwrap().downgrade(ctx))?;
-
-        Ok(expr)
-    }
-}
-
-/// Downgrades a lambda (function) expression.
-/// This involves desugaring pattern-matching arguments into `let` bindings.
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Lambda {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let raw_param = self.param().unwrap();
-        let arg = ctx.new_arg(raw_param.syntax().text_range());
-
-        ctx.push_thunk_scope();
-
-        let param;
-        let body;
-
-        match raw_param {
-            ast::Param::IdentParam(id) => {
-                // Simple case: `x: body`
-                let param_sym = ctx.new_sym(id.to_string());
-                param = None;
-
-                // Downgrade body in Param scope
-                body = ctx
-                    .with_param_scope(param_sym, arg, |ctx| self.body().unwrap().downgrade(ctx))?;
-            }
-            ast::Param::Pattern(pattern) => {
-                let alias = pattern
-                    .pat_bind()
-                    .map(|alias| ctx.new_sym(alias.ident().unwrap().to_string()));
-
-                let ellipsis = pattern.ellipsis_token().is_some();
-                let pat_entries = pattern.pat_entries();
-
-                let PatternBindings {
-                    body: inner_body,
-                    required,
-                    optional,
-                } = downgrade_pattern_bindings(pat_entries, alias, arg, ctx, |ctx, _| {
-                    self.body().unwrap().downgrade(ctx)
-                })?;
-
-                param = Some(Param {
-                    required,
-                    optional,
-                    ellipsis,
-                });
-
-                body = inner_body;
-            }
-        }
-
-        let thunks = ctx.pop_thunk_scope();
-        let span = self.syntax().text_range();
-        Ok(ctx.new_expr(
-            Func {
-                body,
-                param,
-                arg,
-                thunks,
-                span,
-            }
-            .to_ir(),
-        ))
-    }
-}
-
-/// Downgrades a function application.
-/// In Nix, function application is left-associative, so `f a b` should be parsed as `((f a) b)`.
-/// Each Apply node represents a single function call with one argument.
-impl<Ctx: DowngradeContext> Downgrade<Ctx> for ast::Apply {
-    fn downgrade(self, ctx: &mut Ctx) -> Result<ExprId> {
-        let func = self.lambda().unwrap().downgrade(ctx)?;
-        let arg = self.argument().unwrap().downgrade(ctx)?;
-        let arg = ctx.maybe_thunk(arg);
-        let span = self.syntax().text_range();
-        Ok(ctx.new_expr(Call { func, arg, span }.to_ir()))
-    }
-}
diff --git a/nix-js/src/lib.rs b/nix-js/src/lib.rs
index 2f729c1..c627c50 100644
--- a/nix-js/src/lib.rs
+++ b/nix-js/src/lib.rs
@@ -6,6 +6,7 @@ pub mod logging;
 pub mod value;
 
 mod codegen;
+mod downgrade;
 mod fetcher;
 mod ir;
 mod nar;
diff --git a/nix-js/src/runtime.rs b/nix-js/src/runtime.rs
index 9e22c10..496cca3 100644
--- a/nix-js/src/runtime.rs
+++ b/nix-js/src/runtime.rs
@@ -332,7 +332,7 @@ fn to_value<'a>(
                     let val = val.get(scope, key).expect("infallible operation");
                     let key = key.to_rust_string_lossy(scope);
                     (
-                        Symbol::new(key),
+                        Symbol::from(key),
                         to_value(
                             val,
                             scope,
diff --git a/nix-js/src/value.rs b/nix-js/src/value.rs
index 9165704..ad63573 100644
--- a/nix-js/src/value.rs
+++ b/nix-js/src/value.rs
@@ -10,11 +10,19 @@ use derive_more::{Constructor, IsVariant, Unwrap};
 
 /// Represents a Nix symbol, which is used as a key in attribute sets.
 #[derive(Debug, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Constructor)]
-pub struct Symbol(String);
+pub struct Symbol<'a>(Cow<'a, str>);
 
-impl<T: Into<String>> From<T> for Symbol {
-    fn from(value: T) -> Self {
-        Symbol(value.into())
+pub type StaticSymbol = Symbol<'static>;
+
+impl From<String> for Symbol<'_> {
+    fn from(value: String) -> Self {
+        Symbol(Cow::Owned(value))
+    }
+}
+
+impl<'a> From<&'a str> for Symbol<'a> {
+    fn from(value: &'a str) -> Self {
+        Symbol(Cow::Borrowed(value))
     }
 }
 
@@ -28,7 +36,7 @@ pub fn format_symbol<'a>(sym: impl Into<Cow<'a, str>>) -> Cow<'a, str> {
     }
 }
 
-impl Display for Symbol {
+impl Display for Symbol<'_> {
     fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
         if self.normal() {
             write!(f, "{}", self.0)
@@ -38,7 +46,7 @@ impl Display for Symbol {
     }
 }
 
-impl Symbol {
+impl Symbol<'_> {
     const NORMAL_REGEX: ere::Regex<1> = ere::compile_regex!("^[a-zA-Z_][a-zA-Z0-9_'-]*$");
     /// Checks if the symbol is a "normal" identifier that doesn't require quotes.
     fn normal(&self) -> bool {
@@ -46,45 +54,33 @@ impl Symbol {
     }
 }
 
-impl Deref for Symbol {
+impl Deref for Symbol<'_> {
     type Target = str;
     fn deref(&self) -> &Self::Target {
         &self.0
     }
 }
 
-impl Symbol {
-    /// Consumes the `Symbol`, returning its inner `String`.
-    pub fn into_inner(self) -> String {
-        self.0
-    }
-
-    /// Returns a reference to the inner `String`.
-    pub fn as_inner(&self) -> &String {
-        &self.0
-    }
-}
-
 /// Represents a Nix attribute set, which is a map from symbols to values.
 #[derive(Constructor, Default, Clone, PartialEq)]
 pub struct AttrSet {
-    data: BTreeMap<Symbol, Value>,
+    data: BTreeMap<StaticSymbol, Value>,
 }
 
 impl AttrSet {
     /// Gets a value by key (string or Symbol).
-    pub fn get(&self, key: impl Into<Symbol>) -> Option<&Value> {
+    pub fn get<'a, 'sym: 'a>(&'a self, key: impl Into<Symbol<'sym>>) -> Option<&'a Value> {
         self.data.get(&key.into())
     }
 
     /// Checks if a key exists in the attribute set.
-    pub fn contains_key(&self, key: impl Into<Symbol>) -> bool {
+    pub fn contains_key<'a, 'sym: 'a>(&'a self, key: impl Into<Symbol<'sym>>) -> bool {
         self.data.contains_key(&key.into())
     }
 }
 
 impl Deref for AttrSet {
-    type Target = BTreeMap<Symbol, Value>;
+    type Target = BTreeMap<StaticSymbol, Value>;
     fn deref(&self) -> &Self::Target {
         &self.data
     }