Merge pull request #46 from typst/parser-ng

Next Generation Parser

4 files changed, 284 insertions, 144 deletions

diff --git a/src/eval/capture.rs b/src/eval/capture.rs
index f0a2b729..e47831df 100644
--- a/src/eval/capture.rs
+++ b/src/eval/capture.rs
@@ -1,8 +1,8 @@
 use std::rc::Rc;
 
 use super::{Scope, Scopes, Value};
-use crate::syntax::visit::{immutable::visit_expr, Visit};
-use crate::syntax::{Expr, Ident};
+use crate::syntax::ast::{ClosureParam, Expr, Ident, Imports, TypedNode};
+use crate::syntax::RedRef;
 
 /// A visitor that captures variable slots.
 pub struct CapturesVisitor<'a> {
@@ -25,32 +25,153 @@ impl<'a> CapturesVisitor<'a> {
     pub fn finish(self) -> Scope {
         self.captures
     }
-}
 
-impl<'ast> Visit<'ast> for CapturesVisitor<'_> {
-    fn visit_expr(&mut self, node: &'ast Expr) {
-        if let Expr::Ident(ident) = node {
-            // Find out whether the name is not locally defined and if so if it
-            // can be captured.
-            if self.internal.get(ident).is_none() {
-                if let Some(slot) = self.external.get(ident) {
-                    self.captures.def_slot(ident.as_str(), Rc::clone(slot));
-                }
+    /// Bind a new internal variable.
+    pub fn bind(&mut self, ident: Ident) {
+        self.internal.def_mut(ident.take(), Value::None);
+    }
+
+    /// Capture a variable if it isn't internal.
+    pub fn capture(&mut self, ident: Ident) {
+        if self.internal.get(&ident).is_none() {
+            if let Some(slot) = self.external.get(&ident) {
+                self.captures.def_slot(ident.take(), Rc::clone(slot));
             }
-        } else {
-            visit_expr(self, node);
         }
     }
 
-    fn visit_binding(&mut self, ident: &'ast Ident) {
-        self.internal.def_mut(ident.as_str(), Value::None);
+    /// Visit any node and collect all captured variables.
+    pub fn visit(&mut self, node: RedRef) {
+        match node.cast() {
+            // Every identifier is a potential variable that we need to capture.
+            // Identifiers that shouldn't count as captures because they
+            // actually bind a new name are handled further below (individually
+            // through the expressions that contain them).
+            Some(Expr::Ident(ident)) => self.capture(ident),
+
+            // A closure contains parameter bindings, which are bound before the
+            // body is evaluated. Take must be taken so that the default values
+            // of named parameters cannot access previous parameter bindings.
+            Some(Expr::Closure(expr)) => {
+                for param in expr.params() {
+                    if let ClosureParam::Named(named) = param {
+                        self.visit(named.expr().as_red());
+                    }
+                }
+
+                for param in expr.params() {
+                    match param {
+                        ClosureParam::Pos(ident) => self.bind(ident),
+                        ClosureParam::Named(named) => self.bind(named.name()),
+                        ClosureParam::Sink(ident) => self.bind(ident),
+                    }
+                }
+
+                self.visit(expr.body().as_red());
+            }
+
+            // A let expression contains a binding, but that binding is only
+            // active after the body is evaluated.
+            Some(Expr::Let(expr)) => {
+                if let Some(init) = expr.init() {
+                    self.visit(init.as_red());
+                }
+                self.bind(expr.binding());
+            }
+
+            // A for loop contains one or two bindings in its pattern. These are
+            // active after the iterable is evaluated but before the body is
+            // evaluated.
+            Some(Expr::For(expr)) => {
+                self.visit(expr.iter().as_red());
+                let pattern = expr.pattern();
+                if let Some(key) = pattern.key() {
+                    self.bind(key);
+                }
+                self.bind(pattern.value());
+                self.visit(expr.body().as_red());
+            }
+
+            // An import contains items, but these are active only after the
+            // path is evaluated.
+            Some(Expr::Import(expr)) => {
+                self.visit(expr.path().as_red());
+                if let Imports::Items(items) = expr.imports() {
+                    for item in items {
+                        self.bind(item);
+                    }
+                }
+            }
+
+            // Blocks and templates create a scope.
+            Some(Expr::Block(_) | Expr::Template(_)) => {
+                self.internal.enter();
+                for child in node.children() {
+                    self.visit(child);
+                }
+                self.internal.exit();
+            }
+
+            // Everything else is traversed from left to right.
+            _ => {
+                for child in node.children() {
+                    self.visit(child);
+                }
+            }
+        }
     }
+}
 
-    fn visit_enter(&mut self) {
-        self.internal.enter();
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::parse::parse;
+    use crate::source::SourceId;
+    use crate::syntax::RedNode;
+
+    #[track_caller]
+    fn test(src: &str, result: &[&str]) {
+        let green = parse(src);
+        let red = RedNode::from_root(green, SourceId::from_raw(0));
+
+        let mut scopes = Scopes::new(None);
+        scopes.def_const("x", 0);
+        scopes.def_const("y", 0);
+        scopes.def_const("z", 0);
+
+        let mut visitor = CapturesVisitor::new(&scopes);
+        visitor.visit(red.as_ref());
+
+        let captures = visitor.finish();
+        let mut names: Vec<_> = captures.iter().map(|(k, _)| k).collect();
+        names.sort();
+
+        assert_eq!(names, result);
     }
 
-    fn visit_exit(&mut self) {
-        self.internal.exit();
+    #[test]
+    fn test_captures() {
+        // Let binding and function definition.
+        test("#let x = x", &["x"]);
+        test("#let x; {x + y}", &["y"]);
+        test("#let f(x, y) = x + y", &[]);
+
+        // Closure with different kinds of params.
+        test("{(x, y) => x + z}", &["z"]);
+        test("{(x: y, z) => x + z}", &["y"]);
+        test("{(..x) => x + y}", &["y"]);
+        test("{(x, y: x + z) => x + y}", &["x", "z"]);
+
+        // For loop.
+        test("#for x in y { x + z }", &["y", "z"]);
+        test("#for x, y in y { x + y }", &["y"]);
+
+        // Import.
+        test("#import x, y from z", &["z"]);
+        test("#import x, y, z from x + y", &["x", "y"]);
+
+        // Scoping.
+        test("{ let x = 1; { let y = 2; y }; x + y }", &["y"]);
+        test("[#let x = 1]#x", &["x"]);
     }
 }
diff --git a/src/eval/mod.rs b/src/eval/mod.rs
index 691e3c49..fda2184e 100644
--- a/src/eval/mod.rs
+++ b/src/eval/mod.rs
@@ -30,16 +30,14 @@ use std::collections::HashMap;
 use std::io;
 use std::mem;
 use std::path::PathBuf;
-use std::rc::Rc;
 
 use crate::diag::{At, Error, StrResult, Trace, Tracepoint, TypResult};
 use crate::geom::{Angle, Fractional, Length, Relative};
 use crate::image::ImageStore;
 use crate::loading::Loader;
-use crate::parse::parse;
 use crate::source::{SourceId, SourceStore};
-use crate::syntax::visit::Visit;
-use crate::syntax::*;
+use crate::syntax::ast::*;
+use crate::syntax::{Span, Spanned};
 use crate::util::RefMutExt;
 use crate::Context;
 
@@ -114,7 +112,7 @@ impl<'a> EvalContext<'a> {
 
         // Parse the file.
         let source = self.sources.get(id);
-        let ast = parse(&source)?;
+        let ast = source.ast()?;
 
         // Prepare the new context.
         let new_scopes = Scopes::new(self.scopes.base);
@@ -122,7 +120,7 @@ impl<'a> EvalContext<'a> {
         self.route.push(id);
 
         // Evaluate the module.
-        let template = Rc::new(ast).eval(self).trace(|| Tracepoint::Import, span)?;
+        let template = ast.eval(self).trace(|| Tracepoint::Import, span)?;
 
         // Restore the old context.
         let new_scopes = mem::replace(&mut self.scopes, old_scopes);
@@ -176,8 +174,8 @@ impl Eval for Expr {
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
         match self {
-            Self::Ident(v) => v.eval(ctx),
             Self::Lit(v) => v.eval(ctx),
+            Self::Ident(v) => v.eval(ctx),
             Self::Array(v) => v.eval(ctx).map(Value::Array),
             Self::Dict(v) => v.eval(ctx).map(Value::Dict),
             Self::Template(v) => v.eval(ctx).map(Value::Template),
@@ -202,17 +200,17 @@ impl Eval for Lit {
     type Output = Value;
 
     fn eval(&self, _: &mut EvalContext) -> TypResult<Self::Output> {
-        Ok(match *self {
-            Self::None(_) => Value::None,
-            Self::Auto(_) => Value::Auto,
-            Self::Bool(_, v) => Value::Bool(v),
-            Self::Int(_, v) => Value::Int(v),
-            Self::Float(_, v) => Value::Float(v),
-            Self::Length(_, v, unit) => Value::Length(Length::with_unit(v, unit)),
-            Self::Angle(_, v, unit) => Value::Angle(Angle::with_unit(v, unit)),
-            Self::Percent(_, v) => Value::Relative(Relative::new(v / 100.0)),
-            Self::Fractional(_, v) => Value::Fractional(Fractional::new(v)),
-            Self::Str(_, ref v) => Value::Str(v.into()),
+        Ok(match self.kind() {
+            LitKind::None => Value::None,
+            LitKind::Auto => Value::Auto,
+            LitKind::Bool(v) => Value::Bool(v),
+            LitKind::Int(v) => Value::Int(v),
+            LitKind::Float(v) => Value::Float(v),
+            LitKind::Length(v, unit) => Value::Length(Length::with_unit(v, unit)),
+            LitKind::Angle(v, unit) => Value::Angle(Angle::with_unit(v, unit)),
+            LitKind::Percent(v) => Value::Relative(Relative::new(v / 100.0)),
+            LitKind::Fractional(v) => Value::Fractional(Fractional::new(v)),
+            LitKind::Str(ref v) => Value::Str(v.into()),
         })
     }
 }
@@ -223,7 +221,7 @@ impl Eval for Ident {
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
         match ctx.scopes.get(self) {
             Some(slot) => Ok(slot.borrow().clone()),
-            None => bail!(self.span, "unknown variable"),
+            None => bail!(self.span(), "unknown variable"),
         }
     }
 }
@@ -232,7 +230,7 @@ impl Eval for ArrayExpr {
     type Output = Array;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        self.items.iter().map(|expr| expr.eval(ctx)).collect()
+        self.items().map(|expr| expr.eval(ctx)).collect()
     }
 }
 
@@ -240,9 +238,8 @@ impl Eval for DictExpr {
     type Output = Dict;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        self.items
-            .iter()
-            .map(|Named { name, expr }| Ok(((&name.string).into(), expr.eval(ctx)?)))
+        self.items()
+            .map(|x| Ok((x.name().take().into(), x.expr().eval(ctx)?)))
             .collect()
     }
 }
@@ -251,7 +248,7 @@ impl Eval for TemplateExpr {
     type Output = Template;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        self.body.eval(ctx)
+        self.body().eval(ctx)
     }
 }
 
@@ -259,7 +256,7 @@ impl Eval for GroupExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        self.expr.eval(ctx)
+        self.expr().eval(ctx)
     }
 }
 
@@ -270,7 +267,7 @@ impl Eval for BlockExpr {
         ctx.scopes.enter();
 
         let mut output = Value::None;
-        for expr in &self.exprs {
+        for expr in self.exprs() {
             let value = expr.eval(ctx)?;
             output = ops::join(output, value).at(expr.span())?;
         }
@@ -285,13 +282,13 @@ impl Eval for UnaryExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        let value = self.expr.eval(ctx)?;
-        let result = match self.op {
+        let value = self.expr().eval(ctx)?;
+        let result = match self.op() {
             UnOp::Pos => ops::pos(value),
             UnOp::Neg => ops::neg(value),
             UnOp::Not => ops::not(value),
         };
-        result.at(self.span)
+        result.at(self.span())
     }
 }
 
@@ -299,7 +296,7 @@ impl Eval for BinaryExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        match self.op {
+        match self.op() {
             BinOp::Add => self.apply(ctx, ops::add),
             BinOp::Sub => self.apply(ctx, ops::sub),
             BinOp::Mul => self.apply(ctx, ops::mul),
@@ -327,17 +324,17 @@ impl BinaryExpr {
     where
         F: FnOnce(Value, Value) -> StrResult<Value>,
     {
-        let lhs = self.lhs.eval(ctx)?;
+        let lhs = self.lhs().eval(ctx)?;
 
         // Short-circuit boolean operations.
-        if (self.op == BinOp::And && lhs == Value::Bool(false))
-            || (self.op == BinOp::Or && lhs == Value::Bool(true))
+        if (self.op() == BinOp::And && lhs == Value::Bool(false))
+            || (self.op() == BinOp::Or && lhs == Value::Bool(true))
         {
             return Ok(lhs);
         }
 
-        let rhs = self.rhs.eval(ctx)?;
-        op(lhs, rhs).at(self.span)
+        let rhs = self.rhs().eval(ctx)?;
+        op(lhs, rhs).at(self.span())
     }
 
     /// Apply an assignment operation.
@@ -345,10 +342,10 @@ impl BinaryExpr {
     where
         F: FnOnce(Value, Value) -> StrResult<Value>,
     {
-        let rhs = self.rhs.eval(ctx)?;
-        let mut target = self.lhs.access(ctx)?;
+        let rhs = self.rhs().eval(ctx)?;
+        let mut target = self.lhs().access(ctx)?;
         let lhs = mem::take(&mut *target);
-        *target = op(lhs, rhs).at(self.span)?;
+        *target = op(lhs, rhs).at(self.span())?;
         Ok(Value::None)
     }
 }
@@ -357,27 +354,27 @@ impl Eval for CallExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        let callee = self.callee.eval(ctx)?;
-        let mut args = self.args.eval(ctx)?;
+        let callee = self.callee().eval(ctx)?;
+        let mut args = self.args().eval(ctx)?;
 
         match callee {
             Value::Array(array) => {
-                array.get(args.into_index()?).map(Value::clone).at(self.span)
+                array.get(args.into_index()?).map(Value::clone).at(self.span())
             }
 
             Value::Dict(dict) => {
-                dict.get(args.into_key()?).map(Value::clone).at(self.span)
+                dict.get(args.into_key()?).map(Value::clone).at(self.span())
             }
 
             Value::Func(func) => {
                 let point = || Tracepoint::Call(func.name().map(ToString::to_string));
-                let value = func.call(ctx, &mut args).trace(point, self.span)?;
+                let value = func.call(ctx, &mut args).trace(point, self.span())?;
                 args.finish()?;
                 Ok(value)
             }
 
             v => bail!(
-                self.callee.span(),
+                self.callee().span(),
                 "expected function or collection, found {}",
                 v.type_name(),
             ),
@@ -389,9 +386,9 @@ impl Eval for CallArgs {
     type Output = Args;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        let mut items = Vec::with_capacity(self.items.len());
+        let mut items = Vec::new();
 
-        for arg in &self.items {
+        for arg in self.items() {
             let span = arg.span();
             match arg {
                 CallArg::Pos(expr) => {
@@ -401,11 +398,11 @@ impl Eval for CallArgs {
                         value: Spanned::new(expr.eval(ctx)?, expr.span()),
                     });
                 }
-                CallArg::Named(Named { name, expr }) => {
+                CallArg::Named(named) => {
                     items.push(Arg {
                         span,
-                        name: Some((&name.string).into()),
-                        value: Spanned::new(expr.eval(ctx)?, expr.span()),
+                        name: Some(named.name().take().into()),
+                        value: Spanned::new(named.expr().eval(ctx)?, named.expr().span()),
                     });
                 }
                 CallArg::Spread(expr) => match expr.eval(ctx)? {
@@ -438,7 +435,7 @@ impl Eval for CallArgs {
             }
         }
 
-        Ok(Args { span: self.span, items })
+        Ok(Args { span: self.span(), items })
     }
 }
 
@@ -446,39 +443,38 @@ impl Eval for ClosureExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        let name = self.name.as_ref().map(|name| name.string.clone());
-
         // Collect captured variables.
         let captured = {
             let mut visitor = CapturesVisitor::new(&ctx.scopes);
-            visitor.visit_closure(self);
+            visitor.visit(self.as_red());
             visitor.finish()
         };
 
         let mut sink = None;
-        let mut params = Vec::with_capacity(self.params.len());
+        let mut params = Vec::new();
 
         // Collect parameters and an optional sink parameter.
-        for param in &self.params {
+        for param in self.params() {
             match param {
                 ClosureParam::Pos(name) => {
-                    params.push((name.string.clone(), None));
+                    params.push((name.take(), None));
                 }
-                ClosureParam::Named(Named { name, expr }) => {
-                    params.push((name.string.clone(), Some(expr.eval(ctx)?)));
+                ClosureParam::Named(named) => {
+                    params.push((named.name().take(), Some(named.expr().eval(ctx)?)));
                 }
                 ClosureParam::Sink(name) => {
                     if sink.is_some() {
-                        bail!(name.span, "only one argument sink is allowed");
+                        bail!(name.span(), "only one argument sink is allowed");
                     }
-                    sink = Some(name.string.clone());
+                    sink = Some(name.take());
                 }
             }
         }
 
         // Clone the body expression so that we don't have a lifetime
         // dependence on the AST.
-        let body = Rc::clone(&self.body);
+        let name = self.name().map(Ident::take);
+        let body = self.body();
 
         // Define the actual function.
         let func = Function::new(name, move |ctx, args| {
@@ -515,8 +511,9 @@ impl Eval for WithExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        let wrapped = self.callee.eval(ctx)?.cast::<Function>().at(self.callee.span())?;
-        let applied = self.args.eval(ctx)?;
+        let callee = self.callee();
+        let wrapped = callee.eval(ctx)?.cast::<Function>().at(callee.span())?;
+        let applied = self.args().eval(ctx)?;
 
         let name = wrapped.name().cloned();
         let func = Function::new(name, move |ctx, args| {
@@ -532,11 +529,11 @@ impl Eval for LetExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        let value = match &self.init {
+        let value = match self.init() {
             Some(expr) => expr.eval(ctx)?,
             None => Value::None,
         };
-        ctx.scopes.def_mut(self.binding.as_str(), value);
+        ctx.scopes.def_mut(self.binding().take(), value);
         Ok(Value::None)
     }
 }
@@ -545,12 +542,10 @@ impl Eval for IfExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        let condition =
-            self.condition.eval(ctx)?.cast::<bool>().at(self.condition.span())?;
-
-        if condition {
-            self.if_body.eval(ctx)
-        } else if let Some(else_body) = &self.else_body {
+        let condition = self.condition();
+        if condition.eval(ctx)?.cast::<bool>().at(condition.span())? {
+            self.if_body().eval(ctx)
+        } else if let Some(else_body) = self.else_body() {
             else_body.eval(ctx)
         } else {
             Ok(Value::None)
@@ -564,9 +559,11 @@ impl Eval for WhileExpr {
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
         let mut output = Value::None;
 
-        while self.condition.eval(ctx)?.cast::<bool>().at(self.condition.span())? {
-            let value = self.body.eval(ctx)?;
-            output = ops::join(output, value).at(self.body.span())?;
+        let condition = self.condition();
+        while condition.eval(ctx)?.cast::<bool>().at(condition.span())? {
+            let body = self.body();
+            let value = body.eval(ctx)?;
+            output = ops::join(output, value).at(body.span())?;
         }
 
         Ok(output)
@@ -584,40 +581,44 @@ impl Eval for ForExpr {
 
                 #[allow(unused_parens)]
                 for ($($value),*) in $iter {
-                    $(ctx.scopes.def_mut($binding.as_str(), $value);)*
+                    $(ctx.scopes.def_mut(&$binding, $value);)*
 
-                    let value = self.body.eval(ctx)?;
+                    let value = self.body().eval(ctx)?;
                     output = ops::join(output, value)
-                        .at(self.body.span())?;
+                        .at(self.body().span())?;
                 }
 
                 ctx.scopes.exit();
-                Ok(output)
+                return Ok(output);
             }};
         }
 
-        let iter = self.iter.eval(ctx)?;
-        match (&self.pattern, iter) {
-            (ForPattern::Value(v), Value::Str(string)) => {
-                iter!(for (v => value) in string.iter())
+        let iter = self.iter().eval(ctx)?;
+        let pattern = self.pattern();
+        let key = pattern.key().map(Ident::take);
+        let value = pattern.value().take();
+
+        match (key, value, iter) {
+            (None, v, Value::Str(string)) => {
+                iter!(for (v => value) in string.iter());
             }
-            (ForPattern::Value(v), Value::Array(array)) => {
-                iter!(for (v => value) in array.into_iter())
+            (None, v, Value::Array(array)) => {
+                iter!(for (v => value) in array.into_iter());
             }
-            (ForPattern::KeyValue(i, v), Value::Array(array)) => {
-                iter!(for (i => idx, v => value) in array.into_iter().enumerate())
+            (Some(i), v, Value::Array(array)) => {
+                iter!(for (i => idx, v => value) in array.into_iter().enumerate());
             }
-            (ForPattern::Value(v), Value::Dict(dict)) => {
-                iter!(for (v => value) in dict.into_iter().map(|p| p.1))
+            (None, v, Value::Dict(dict)) => {
+                iter!(for (v => value) in dict.into_iter().map(|p| p.1));
             }
-            (ForPattern::KeyValue(k, v), Value::Dict(dict)) => {
-                iter!(for (k => key, v => value) in dict.into_iter())
+            (Some(k), v, Value::Dict(dict)) => {
+                iter!(for (k => key, v => value) in dict.into_iter());
             }
-            (ForPattern::KeyValue(_, _), Value::Str(_)) => {
-                bail!(self.pattern.span(), "mismatched pattern");
+            (_, _, Value::Str(_)) => {
+                bail!(pattern.span(), "mismatched pattern");
             }
-            (_, iter) => {
-                bail!(self.iter.span(), "cannot loop over {}", iter.type_name());
+            (_, _, iter) => {
+                bail!(self.iter().span(), "cannot loop over {}", iter.type_name());
             }
         }
     }
@@ -627,23 +628,23 @@ impl Eval for ImportExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        let path = self.path.eval(ctx)?.cast::<Str>().at(self.path.span())?;
-
-        let file = ctx.import(&path, self.path.span())?;
+        let path = self.path();
+        let resolved = path.eval(ctx)?.cast::<Str>().at(path.span())?;
+        let file = ctx.import(&resolved, path.span())?;
         let module = &ctx.modules[&file];
 
-        match &self.imports {
+        match self.imports() {
             Imports::Wildcard => {
                 for (var, slot) in module.scope.iter() {
                     ctx.scopes.def_mut(var, slot.borrow().clone());
                 }
             }
-            Imports::Idents(idents) => {
+            Imports::Items(idents) => {
                 for ident in idents {
                     if let Some(slot) = module.scope.get(&ident) {
-                        ctx.scopes.def_mut(ident.as_str(), slot.borrow().clone());
+                        ctx.scopes.def_mut(ident.take(), slot.borrow().clone());
                     } else {
-                        bail!(ident.span, "unresolved import");
+                        bail!(ident.span(), "unresolved import");
                     }
                 }
             }
@@ -657,11 +658,10 @@ impl Eval for IncludeExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> TypResult<Self::Output> {
-        let path = self.path.eval(ctx)?.cast::<Str>().at(self.path.span())?;
-
-        let file = ctx.import(&path, self.path.span())?;
+        let path = self.path();
+        let resolved = path.eval(ctx)?.cast::<Str>().at(path.span())?;
+        let file = ctx.import(&resolved, path.span())?;
         let module = &ctx.modules[&file];
-
         Ok(Value::Template(module.template.clone()))
     }
 }
@@ -689,23 +689,23 @@ impl Access for Ident {
         match ctx.scopes.get(self) {
             Some(slot) => match slot.try_borrow_mut() {
                 Ok(guard) => Ok(guard),
-                Err(_) => bail!(self.span, "cannot mutate a constant"),
+                Err(_) => bail!(self.span(), "cannot mutate a constant"),
             },
-            None => bail!(self.span, "unknown variable"),
+            None => bail!(self.span(), "unknown variable"),
         }
     }
 }
 
 impl Access for CallExpr {
     fn access<'a>(&self, ctx: &'a mut EvalContext) -> TypResult<RefMut<'a, Value>> {
-        let args = self.args.eval(ctx)?;
-        let guard = self.callee.access(ctx)?;
+        let args = self.args().eval(ctx)?;
+        let guard = self.callee().access(ctx)?;
 
         RefMut::try_map(guard, |value| match value {
-            Value::Array(array) => array.get_mut(args.into_index()?).at(self.span),
+            Value::Array(array) => array.get_mut(args.into_index()?).at(self.span()),
             Value::Dict(dict) => Ok(dict.get_mut(args.into_key()?)),
             v => bail!(
-                self.callee.span(),
+                self.callee().span(),
                 "expected collection, found {}",
                 v.type_name(),
             ),
diff --git a/src/eval/scope.rs b/src/eval/scope.rs
index eb057ae3..2290affd 100644
--- a/src/eval/scope.rs
+++ b/src/eval/scope.rs
@@ -120,6 +120,8 @@ impl Scope {
 
 impl Debug for Scope {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        self.values.fmt(f)
+        f.debug_map()
+            .entries(self.values.iter().map(|(k, v)| (k, v.borrow())))
+            .finish()
     }
 }
diff --git a/src/eval/walk.rs b/src/eval/walk.rs
index 96138338..aab32f40 100644
--- a/src/eval/walk.rs
+++ b/src/eval/walk.rs
@@ -5,7 +5,7 @@ use crate::diag::TypResult;
 use crate::geom::Spec;
 use crate::layout::BlockLevel;
 use crate::library::{GridNode, ParChild, ParNode, TrackSizing};
-use crate::syntax::*;
+use crate::syntax::ast::*;
 use crate::util::BoolExt;
 
 /// Walk markup, filling the currently built template.
@@ -16,7 +16,7 @@ pub trait Walk {
 
 impl Walk for Markup {
     fn walk(&self, ctx: &mut EvalContext) -> TypResult<()> {
-        for node in self.iter() {
+        for node in self.nodes() {
             node.walk(ctx)?;
         }
         Ok(())
@@ -27,12 +27,13 @@ impl Walk for MarkupNode {
     fn walk(&self, ctx: &mut EvalContext) -> TypResult<()> {
         match self {
             Self::Space => ctx.template.space(),
-            Self::Linebreak(_) => ctx.template.linebreak(),
-            Self::Parbreak(_) => ctx.template.parbreak(),
-            Self::Strong(_) => ctx.template.modify(|s| s.text_mut().strong.flip()),
-            Self::Emph(_) => ctx.template.modify(|s| s.text_mut().emph.flip()),
+            Self::Linebreak => ctx.template.linebreak(),
+            Self::Parbreak => ctx.template.parbreak(),
+            Self::Strong => ctx.template.modify(|s| s.text_mut().strong.flip()),
+            Self::Emph => ctx.template.modify(|s| s.text_mut().emph.flip()),
             Self::Text(text) => ctx.template.text(text),
             Self::Raw(raw) => raw.walk(ctx)?,
+            Self::Math(math) => math.walk(ctx)?,
             Self::Heading(heading) => heading.walk(ctx)?,
             Self::List(list) => list.walk(ctx)?,
             Self::Enum(enum_) => enum_.walk(ctx)?,
@@ -67,16 +68,32 @@ impl Walk for RawNode {
     }
 }
 
+impl Walk for MathNode {
+    fn walk(&self, ctx: &mut EvalContext) -> TypResult<()> {
+        if self.display {
+            ctx.template.parbreak();
+        }
+
+        ctx.template.monospace(self.formula.trim());
+
+        if self.display {
+            ctx.template.parbreak();
+        }
+
+        Ok(())
+    }
+}
+
 impl Walk for HeadingNode {
     fn walk(&self, ctx: &mut EvalContext) -> TypResult<()> {
-        let level = self.level;
-        let body = self.body.eval(ctx)?;
+        let level = self.level();
+        let body = self.body().eval(ctx)?;
 
         ctx.template.parbreak();
         ctx.template.save();
         ctx.template.modify(move |style| {
             let text = style.text_mut();
-            let upscale = 1.6 - 0.1 * level as f64;
+            let upscale = (1.6 - 0.1 * level as f64).max(0.75);
             text.size *= upscale;
             text.strong = true;
         });
@@ -90,7 +107,7 @@ impl Walk for HeadingNode {
 
 impl Walk for ListNode {
     fn walk(&self, ctx: &mut EvalContext) -> TypResult<()> {
-        let body = self.body.eval(ctx)?;
+        let body = self.body().eval(ctx)?;
         walk_item(ctx, Str::from('•'), body);
         Ok(())
     }
@@ -98,8 +115,8 @@ impl Walk for ListNode {
 
 impl Walk for EnumNode {
     fn walk(&self, ctx: &mut EvalContext) -> TypResult<()> {
-        let body = self.body.eval(ctx)?;
-        let label = format_str!("{}.", self.number.unwrap_or(1));
+        let body = self.body().eval(ctx)?;
+        let label = format_str!("{}.", self.number().unwrap_or(1));
         walk_item(ctx, label, body);
         Ok(())
     }