Merge pull request #46 from typst/parser-ng

Next Generation Parser

33 files changed, 3391 insertions, 2703 deletions

diff --git a/benches/oneshot.rs b/benches/oneshot.rs
index 6ce81a63..bb385688 100644
--- a/benches/oneshot.rs
+++ b/benches/oneshot.rs
@@ -6,7 +6,7 @@ use typst::eval::eval;
 use typst::layout::layout;
 use typst::loading::MemLoader;
 use typst::parse::{parse, Scanner, TokenMode, Tokens};
-use typst::source::{SourceFile, SourceId};
+use typst::source::SourceId;
 use typst::Context;
 
 const SRC: &str = include_str!("bench.typ");
@@ -48,12 +48,12 @@ fn bench_tokenize(iai: &mut Iai) {
 }
 
 fn bench_parse(iai: &mut Iai) {
-    iai.run(|| parse(&SourceFile::detached(SRC)));
+    iai.run(|| parse(SRC));
 }
 
 fn bench_eval(iai: &mut Iai) {
     let (mut ctx, id) = context();
-    let ast = ctx.parse(id).unwrap();
+    let ast = ctx.sources.get(id).ast().unwrap();
     iai.run(|| eval(&mut ctx, id, &ast).unwrap());
 }
 
diff --git a/src/diag.rs b/src/diag.rs
index f0455310..d284687e 100644
--- a/src/diag.rs
+++ b/src/diag.rs
@@ -100,7 +100,7 @@ impl<T> Trace<T> for TypResult<T> {
     {
         self.map_err(|mut errors| {
             for error in errors.iter_mut() {
-                if !span.contains(error.span) {
+                if !span.surrounds(error.span) {
                     error.trace.push(Spanned::new(make_point(), span));
                 }
             }
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(())
     }
diff --git a/src/geom/relative.rs b/src/geom/relative.rs
index c2d0a0cb..e46c51de 100644
--- a/src/geom/relative.rs
+++ b/src/geom/relative.rs
@@ -3,7 +3,7 @@ use super::*;
 /// A relative length.
 ///
 /// _Note_: `50%` is represented as `0.5` here, but stored as `50.0` in the
-/// corresponding [literal](crate::syntax::Lit::Percent).
+/// corresponding [literal](crate::syntax::ast::LitKind::Percent).
 #[derive(Default, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
 pub struct Relative(N64);
 
diff --git a/src/lib.rs b/src/lib.rs
index 41b2e88b..033230f0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -20,7 +20,7 @@
 //!
 //! [tokens]: parse::Tokens
 //! [parsed]: parse::parse
-//! [markup]: syntax::Markup
+//! [markup]: syntax::ast::Markup
 //! [evaluate]: eval::eval
 //! [module]: eval::Module
 //! [layout tree]: layout::LayoutTree
@@ -58,7 +58,6 @@ use crate::layout::{EvictionPolicy, LayoutCache};
 use crate::loading::Loader;
 use crate::source::{SourceId, SourceStore};
 use crate::style::Style;
-use crate::syntax::Markup;
 
 /// The core context which holds the loader, configuration and cached artifacts.
 pub struct Context {
@@ -100,14 +99,9 @@ impl Context {
         &self.style
     }
 
-    /// Parse a source file and return the resulting markup.
-    pub fn parse(&mut self, id: SourceId) -> TypResult<Markup> {
-        parse::parse(self.sources.get(id))
-    }
-
     /// Evaluate a source file and return the resulting module.
     pub fn evaluate(&mut self, id: SourceId) -> TypResult<Module> {
-        let ast = self.parse(id)?;
+        let ast = self.sources.get(id).ast()?;
         eval::eval(self, id, &ast)
     }
 
diff --git a/src/parse/mod.rs b/src/parse/mod.rs
index 30787423..f9c0049f 100644
--- a/src/parse/mod.rs
+++ b/src/parse/mod.rs
@@ -12,216 +12,162 @@ pub use tokens::*;
 
 use std::rc::Rc;
 
-use crate::diag::TypResult;
-use crate::source::SourceFile;
-use crate::syntax::*;
-use crate::util::EcoString;
+use crate::syntax::ast::{Associativity, BinOp, UnOp};
+use crate::syntax::{ErrorPos, Green, GreenNode, NodeKind};
 
 /// Parse a source file.
-pub fn parse(source: &SourceFile) -> TypResult<Markup> {
-    let mut p = Parser::new(source);
-    let markup = markup(&mut p);
-    let errors = p.finish();
-    if errors.is_empty() {
-        Ok(markup)
-    } else {
-        Err(Box::new(errors))
+pub fn parse(src: &str) -> Rc<GreenNode> {
+    let mut p = Parser::new(src);
+    markup(&mut p);
+    match p.finish().into_iter().next() {
+        Some(Green::Node(node)) => node,
+        _ => unreachable!(),
     }
 }
 
 /// Parse markup.
-fn markup(p: &mut Parser) -> Markup {
+fn markup(p: &mut Parser) {
     markup_while(p, true, &mut |_| true)
 }
 
-/// Parse markup that stays equal or right of the given column.
-fn markup_indented(p: &mut Parser, column: usize) -> Markup {
+/// Parse markup that stays right of the given column.
+fn markup_indented(p: &mut Parser, column: usize) {
     p.eat_while(|t| match t {
-        Token::Space(n) => n == 0,
-        Token::LineComment(_) | Token::BlockComment(_) => true,
+        NodeKind::Space(n) => *n == 0,
+        NodeKind::LineComment | NodeKind::BlockComment => true,
         _ => false,
     });
 
     markup_while(p, false, &mut |p| match p.peek() {
-        Some(Token::Space(n)) if n >= 1 => p.column(p.next_end()) >= column,
+        Some(NodeKind::Space(n)) if *n >= 1 => p.column(p.current_end()) >= column,
         _ => true,
     })
 }
 
-/// Parse a syntax tree while the peeked token satisifies a condition.
+/// Parse a syntax tree while the peeked NodeKind satisifies a condition.
 ///
 /// If `at_start` is true, things like headings that may only appear at the
 /// beginning of a line or template are allowed.
-fn markup_while<F>(p: &mut Parser, mut at_start: bool, f: &mut F) -> Markup
+fn markup_while<F>(p: &mut Parser, mut at_start: bool, f: &mut F)
 where
     F: FnMut(&mut Parser) -> bool,
 {
-    let mut tree = vec![];
-    while !p.eof() && f(p) {
-        if let Some(node) = markup_node(p, &mut at_start) {
-            at_start &= matches!(node, MarkupNode::Space | MarkupNode::Parbreak(_));
-            tree.push(node);
+    p.perform(NodeKind::Markup, |p| {
+        while !p.eof() && f(p) {
+            markup_node(p, &mut at_start);
         }
-    }
-
-    tree
+    });
 }
 
 /// Parse a markup node.
-fn markup_node(p: &mut Parser, at_start: &mut bool) -> Option<MarkupNode> {
-    let token = p.peek()?;
-    let span = p.peek_span();
-    let node = match token {
+fn markup_node(p: &mut Parser, at_start: &mut bool) {
+    let token = match p.peek() {
+        Some(t) => t,
+        None => return,
+    };
+
+    match token {
         // Whitespace.
-        Token::Space(newlines) => {
-            *at_start |= newlines > 0;
-            if newlines < 2 {
-                MarkupNode::Space
+        NodeKind::Space(newlines) => {
+            *at_start |= *newlines > 0;
+            if *newlines < 2 {
+                p.eat();
             } else {
-                MarkupNode::Parbreak(span)
+                p.convert(NodeKind::Parbreak);
             }
+            return;
         }
 
-        // Text.
-        Token::Text(text) => MarkupNode::Text(text.into()),
-        Token::Tilde => MarkupNode::Text("\u{00A0}".into()),
-        Token::HyphHyph => MarkupNode::Text("\u{2013}".into()),
-        Token::HyphHyphHyph => MarkupNode::Text("\u{2014}".into()),
-        Token::UnicodeEscape(t) => MarkupNode::Text(unicode_escape(p, t)),
+        // Comments.
+        NodeKind::LineComment | NodeKind::BlockComment => {
+            p.eat();
+            return;
+        }
+
+        // Text and markup.
+        NodeKind::Text(_)
+        | NodeKind::EnDash
+        | NodeKind::EmDash
+        | NodeKind::NonBreakingSpace
+        | NodeKind::Emph
+        | NodeKind::Strong
+        | NodeKind::Linebreak
+        | NodeKind::Raw(_)
+        | NodeKind::Math(_)
+        | NodeKind::UnicodeEscape(_) => {
+            p.eat();
+        }
 
-        // Markup.
-        Token::Backslash => MarkupNode::Linebreak(span),
-        Token::Star => MarkupNode::Strong(span),
-        Token::Underscore => MarkupNode::Emph(span),
-        Token::Raw(t) => raw(p, t),
-        Token::Eq if *at_start => return Some(heading(p)),
-        Token::Hyph if *at_start => return Some(list_node(p)),
-        Token::Numbering(number) if *at_start => return Some(enum_node(p, number)),
+        NodeKind::Eq if *at_start => heading(p),
+        NodeKind::Minus if *at_start => list_node(p),
+        NodeKind::EnumNumbering(_) if *at_start => enum_node(p),
 
         // Line-based markup that is not currently at the start of the line.
-        Token::Eq | Token::Hyph | Token::Numbering(_) => {
-            MarkupNode::Text(p.peek_src().into())
+        NodeKind::Eq | NodeKind::Minus | NodeKind::EnumNumbering(_) => {
+            p.convert(NodeKind::Text(p.peek_src().into()));
         }
 
         // Hashtag + keyword / identifier.
-        Token::Ident(_)
-        | Token::Let
-        | Token::If
-        | Token::While
-        | Token::For
-        | Token::Import
-        | Token::Include => {
-            let stmt = matches!(token, Token::Let | Token::Import);
+        NodeKind::Ident(_)
+        | NodeKind::Let
+        | NodeKind::If
+        | NodeKind::While
+        | NodeKind::For
+        | NodeKind::Import
+        | NodeKind::Include => {
+            let stmt = matches!(token, NodeKind::Let | NodeKind::Import);
             let group = if stmt { Group::Stmt } else { Group::Expr };
 
-            p.start_group(group, TokenMode::Code);
-            let expr = expr_with(p, true, 0);
-            if stmt && expr.is_some() && !p.eof() {
-                p.expected_at(p.prev_end(), "semicolon or line break");
+            p.start_group(group);
+            let res = expr_prec(p, true, 0);
+            if stmt && res.is_ok() && !p.eof() {
+                p.expected_at("semicolon or line break");
             }
             p.end_group();
-
-            return expr.map(MarkupNode::Expr);
         }
 
         // Block and template.
-        Token::LeftBrace => return Some(MarkupNode::Expr(block(p))),
-        Token::LeftBracket => return Some(MarkupNode::Expr(template(p))),
-
-        // Comments.
-        Token::LineComment(_) | Token::BlockComment(_) => {
-            p.eat();
-            return None;
-        }
+        NodeKind::LeftBrace => block(p),
+        NodeKind::LeftBracket => template(p),
 
-        _ => {
-            *at_start = false;
-            p.unexpected();
-            return None;
-        }
+        NodeKind::Error(_, _) => p.eat(),
+        _ => p.unexpected(),
     };
-    p.eat();
-    Some(node)
-}
 
-/// Handle a unicode escape sequence.
-fn unicode_escape(p: &mut Parser, token: UnicodeEscapeToken) -> EcoString {
-    let span = p.peek_span();
-    let text = if let Some(c) = resolve::resolve_hex(token.sequence) {
-        c.into()
-    } else {
-        // Print out the escape sequence verbatim if it is invalid.
-        p.error(span, "invalid unicode escape sequence");
-        p.peek_src().into()
-    };
-
-    if !token.terminated {
-        p.error(span.end, "expected closing brace");
-    }
-
-    text
-}
-
-/// Handle a raw block.
-fn raw(p: &mut Parser, token: RawToken) -> MarkupNode {
-    let column = p.column(p.next_start());
-    let span = p.peek_span();
-    let raw = resolve::resolve_raw(span, column, token.backticks, token.text);
-    if !token.terminated {
-        p.error(span.end, "expected backtick(s)");
-    }
-    MarkupNode::Raw(Box::new(raw))
+    *at_start = false;
 }
 
 /// Parse a heading.
-fn heading(p: &mut Parser) -> MarkupNode {
-    let start = p.next_start();
-    p.eat_assert(Token::Eq);
-
-    // Count depth.
-    let mut level: usize = 1;
-    while p.eat_if(Token::Eq) {
-        level += 1;
-    }
-
-    if level > 6 {
-        return MarkupNode::Text(p.get(start .. p.prev_end()).into());
-    }
-
-    let column = p.column(p.prev_end());
-    let body = markup_indented(p, column);
-    MarkupNode::Heading(Box::new(HeadingNode {
-        span: p.span_from(start),
-        level,
-        body,
-    }))
+fn heading(p: &mut Parser) {
+    p.perform(NodeKind::Heading, |p| {
+        p.eat_assert(&NodeKind::Eq);
+        while p.eat_if(&NodeKind::Eq) {}
+        let column = p.column(p.prev_end());
+        markup_indented(p, column);
+    });
 }
 
 /// Parse a single list item.
-fn list_node(p: &mut Parser) -> MarkupNode {
-    let start = p.next_start();
-    p.eat_assert(Token::Hyph);
-    let column = p.column(p.prev_end());
-    let body = markup_indented(p, column);
-    MarkupNode::List(Box::new(ListNode { span: p.span_from(start), body }))
+fn list_node(p: &mut Parser) {
+    p.perform(NodeKind::List, |p| {
+        p.eat_assert(&NodeKind::Minus);
+        let column = p.column(p.prev_end());
+        markup_indented(p, column);
+    });
 }
 
 /// Parse a single enum item.
-fn enum_node(p: &mut Parser, number: Option<usize>) -> MarkupNode {
-    let start = p.next_start();
-    p.eat_assert(Token::Numbering(number));
-    let column = p.column(p.prev_end());
-    let body = markup_indented(p, column);
-    MarkupNode::Enum(Box::new(EnumNode {
-        span: p.span_from(start),
-        number,
-        body,
-    }))
+fn enum_node(p: &mut Parser) {
+    p.perform(NodeKind::Enum, |p| {
+        p.eat();
+        let column = p.column(p.prev_end());
+        markup_indented(p, column);
+    });
 }
 
 /// Parse an expression.
-fn expr(p: &mut Parser) -> Option<Expr> {
-    expr_with(p, false, 0)
+fn expr(p: &mut Parser) -> ParseResult {
+    expr_prec(p, false, 0)
 }
 
 /// Parse an expression with operators having at least the minimum precedence.
@@ -231,13 +177,16 @@ fn expr(p: &mut Parser) -> Option<Expr> {
 /// in markup.
 ///
 /// Stops parsing at operations with lower precedence than `min_prec`,
-fn expr_with(p: &mut Parser, atomic: bool, min_prec: usize) -> Option<Expr> {
-    let start = p.next_start();
-    let mut lhs = match p.eat_map(UnOp::from_token) {
+fn expr_prec(p: &mut Parser, atomic: bool, min_prec: usize) -> ParseResult {
+    let marker = p.marker();
+
+    // Start the unary expression.
+    match p.peek().and_then(UnOp::from_token) {
         Some(op) => {
+            p.eat();
             let prec = op.precedence();
-            let expr = expr_with(p, atomic, prec)?;
-            Expr::Unary(Box::new(UnaryExpr { span: p.span_from(start), op, expr }))
+            expr_prec(p, atomic, prec)?;
+            marker.end(p, NodeKind::Unary);
         }
         None => primary(p, atomic)?,
     };
@@ -245,19 +194,19 @@ fn expr_with(p: &mut Parser, atomic: bool, min_prec: usize) -> Option<Expr> {
     loop {
         // Exclamation mark, parenthesis or bracket means this is a function
         // call.
-        if matches!(p.peek_direct(), Some(Token::LeftParen | Token::LeftBracket)) {
-            lhs = call(p, lhs)?;
+        if let Some(NodeKind::LeftParen | NodeKind::LeftBracket) = p.peek_direct() {
+            call(p, marker)?;
             continue;
         }
 
-        if p.eat_if(Token::With) {
-            lhs = with_expr(p, lhs)?;
-        }
-
         if atomic {
             break;
         }
 
+        if p.at(&NodeKind::With) {
+            with_expr(p, marker)?;
+        }
+
         let op = match p.peek().and_then(BinOp::from_token) {
             Some(binop) => binop,
             None => break,
@@ -269,96 +218,94 @@ fn expr_with(p: &mut Parser, atomic: bool, min_prec: usize) -> Option<Expr> {
         }
 
         p.eat();
+
         match op.associativity() {
             Associativity::Left => prec += 1,
             Associativity::Right => {}
         }
 
-        let rhs = match expr_with(p, atomic, prec) {
-            Some(rhs) => rhs,
-            None => break,
-        };
-
-        let span = lhs.span().join(rhs.span());
-        lhs = Expr::Binary(Box::new(BinaryExpr { span, lhs, op, rhs }));
+        marker.perform(p, NodeKind::Binary, |p| expr_prec(p, atomic, prec))?;
     }
 
-    Some(lhs)
+    Ok(())
 }
 
 /// Parse a primary expression.
-fn primary(p: &mut Parser, atomic: bool) -> Option<Expr> {
-    if let Some(expr) = literal(p) {
-        return Some(expr);
+fn primary(p: &mut Parser, atomic: bool) -> ParseResult {
+    if literal(p) {
+        return Ok(());
     }
 
     match p.peek() {
         // Things that start with an identifier.
-        Some(Token::Ident(string)) => {
-            let ident = Ident {
-                span: p.eat_span(),
-                string: string.into(),
-            };
+        Some(NodeKind::Ident(_)) => {
+            let marker = p.marker();
+            p.eat();
 
             // Arrow means this is a closure's lone parameter.
-            Some(if !atomic && p.eat_if(Token::Arrow) {
-                let body = expr(p)?;
-                Expr::Closure(Box::new(ClosureExpr {
-                    span: ident.span.join(body.span()),
-                    name: None,
-                    params: vec![ClosureParam::Pos(ident)],
-                    body: Rc::new(body),
-                }))
+            if !atomic && p.at(&NodeKind::Arrow) {
+                marker.end(p, NodeKind::ClosureParams);
+                p.eat_assert(&NodeKind::Arrow);
+                marker.perform(p, NodeKind::Closure, expr)
             } else {
-                Expr::Ident(Box::new(ident))
-            })
+                Ok(())
+            }
         }
 
         // Structures.
-        Some(Token::LeftParen) => parenthesized(p),
-        Some(Token::LeftBracket) => Some(template(p)),
-        Some(Token::LeftBrace) => Some(block(p)),
+        Some(NodeKind::LeftParen) => parenthesized(p),
+        Some(NodeKind::LeftBracket) => {
+            template(p);
+            Ok(())
+        }
+        Some(NodeKind::LeftBrace) => {
+            block(p);
+            Ok(())
+        }
 
         // Keywords.
-        Some(Token::Let) => let_expr(p),
-        Some(Token::If) => if_expr(p),
-        Some(Token::While) => while_expr(p),
-        Some(Token::For) => for_expr(p),
-        Some(Token::Import) => import_expr(p),
-        Some(Token::Include) => include_expr(p),
+        Some(NodeKind::Let) => let_expr(p),
+        Some(NodeKind::If) => if_expr(p),
+        Some(NodeKind::While) => while_expr(p),
+        Some(NodeKind::For) => for_expr(p),
+        Some(NodeKind::Import) => import_expr(p),
+        Some(NodeKind::Include) => include_expr(p),
+
+        Some(NodeKind::Error(_, _)) => {
+            p.eat();
+            Err(())
+        }
 
         // Nothing.
         _ => {
             p.expected("expression");
-            None
+            Err(())
         }
     }
 }
 
 /// Parse a literal.
-fn literal(p: &mut Parser) -> Option<Expr> {
-    let span = p.peek_span();
-    let lit = match p.peek()? {
+fn literal(p: &mut Parser) -> bool {
+    match p.peek() {
         // Basic values.
-        Token::None => Lit::None(span),
-        Token::Auto => Lit::Auto(span),
-        Token::Bool(b) => Lit::Bool(span, b),
-        Token::Int(i) => Lit::Int(span, i),
-        Token::Float(f) => Lit::Float(span, f),
-        Token::Length(val, unit) => Lit::Length(span, val, unit),
-        Token::Angle(val, unit) => Lit::Angle(span, val, unit),
-        Token::Percent(p) => Lit::Percent(span, p),
-        Token::Fraction(p) => Lit::Fractional(span, p),
-        Token::Str(token) => Lit::Str(span, {
-            if !token.terminated {
-                p.expected_at(span.end, "quote");
-            }
-            resolve::resolve_string(token.string)
-        }),
-        _ => return None,
-    };
-    p.eat();
-    Some(Expr::Lit(Box::new(lit)))
+        Some(
+            NodeKind::None
+            | NodeKind::Auto
+            | NodeKind::Int(_)
+            | NodeKind::Float(_)
+            | NodeKind::Bool(_)
+            | NodeKind::Fraction(_)
+            | NodeKind::Length(_, _)
+            | NodeKind::Angle(_, _)
+            | NodeKind::Percentage(_)
+            | NodeKind::Str(_),
+        ) => {
+            p.eat();
+            true
+        }
+
+        _ => false,
+    }
 }
 
 /// Parse something that starts with a parenthesis, which can be either of:
@@ -366,433 +313,395 @@ fn literal(p: &mut Parser) -> Option<Expr> {
 /// - Dictionary literal
 /// - Parenthesized expression
 /// - Parameter list of closure expression
-fn parenthesized(p: &mut Parser) -> Option<Expr> {
-    p.start_group(Group::Paren, TokenMode::Code);
-    let colon = p.eat_if(Token::Colon);
-    let (items, has_comma) = collection(p);
-    let span = p.end_group();
+fn parenthesized(p: &mut Parser) -> ParseResult {
+    let marker = p.marker();
 
-    // Leading colon makes this a dictionary.
+    p.start_group(Group::Paren);
+    let colon = p.eat_if(&NodeKind::Colon);
+    let kind = collection(p).0;
+    p.end_group();
+
+    // Leading colon makes this a (empty) dictionary.
     if colon {
-        return Some(dict(p, items, span));
+        dict(p, marker);
+        return Ok(());
     }
 
     // Arrow means this is a closure's parameter list.
-    if p.eat_if(Token::Arrow) {
-        let params = params(p, items);
-        let body = expr(p)?;
-        return Some(Expr::Closure(Box::new(ClosureExpr {
-            span: span.join(body.span()),
-            name: None,
-            params,
-            body: Rc::new(body),
-        })));
+    if p.at(&NodeKind::Arrow) {
+        params(p, marker);
+        p.eat_assert(&NodeKind::Arrow);
+        return marker.perform(p, NodeKind::Closure, expr);
     }
 
-    // Find out which kind of collection this is.
-    Some(match items.as_slice() {
-        [] => array(p, items, span),
-        [CallArg::Pos(_)] if !has_comma => match items.into_iter().next() {
-            Some(CallArg::Pos(expr)) => Expr::Group(Box::new(GroupExpr { span, expr })),
-            _ => unreachable!(),
-        },
-        [CallArg::Pos(_), ..] => array(p, items, span),
-        [CallArg::Named(_), ..] => dict(p, items, span),
-        [CallArg::Spread(expr), ..] => {
-            p.error(expr.span(), "spreading is not allowed here");
-            return None;
-        }
-    })
+    // Transform into the identified collection.
+    match kind {
+        CollectionKind::Group => marker.end(p, NodeKind::Group),
+        CollectionKind::Positional => array(p, marker),
+        CollectionKind::Named => dict(p, marker),
+    }
+
+    Ok(())
+}
+
+/// The type of a collection.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+enum CollectionKind {
+    /// The collection is only one item and has no comma.
+    Group,
+    /// The collection starts with a positional and has more items or a trailing
+    /// comma.
+    Positional,
+    /// The collection starts with a named item.
+    Named,
 }
 
 /// Parse a collection.
 ///
-/// Returns whether the literal contained any commas.
-fn collection(p: &mut Parser) -> (Vec<CallArg>, bool) {
-    let mut items = vec![];
-    let mut has_comma = false;
-    let mut missing_coma = None;
+/// Returns the length of the collection and whether the literal contained any
+/// commas.
+fn collection(p: &mut Parser) -> (CollectionKind, usize) {
+    let mut kind = CollectionKind::Positional;
+    let mut items = 0;
+    let mut can_group = true;
+    let mut error = false;
+    let mut missing_coma: Option<Marker> = None;
 
     while !p.eof() {
-        if let Some(arg) = item(p) {
-            items.push(arg);
+        if let Ok(item_kind) = item(p) {
+            if items == 0 && item_kind == NodeKind::Named {
+                kind = CollectionKind::Named;
+                can_group = false;
+            }
 
-            if let Some(pos) = missing_coma.take() {
-                p.expected_at(pos, "comma");
+            if item_kind == NodeKind::Spread {
+                can_group = false;
+            }
+
+            items += 1;
+
+            if let Some(marker) = missing_coma.take() {
+                marker.expected(p, "comma");
             }
 
             if p.eof() {
                 break;
             }
 
-            let behind = p.prev_end();
-            if p.eat_if(Token::Comma) {
-                has_comma = true;
+            if p.eat_if(&NodeKind::Comma) {
+                can_group = false;
             } else {
-                missing_coma = Some(behind);
+                missing_coma = Some(p.trivia_start());
             }
+        } else {
+            error = true;
         }
     }
 
-    (items, has_comma)
+    if error || (can_group && items == 1) {
+        kind = CollectionKind::Group;
+    }
+
+    (kind, items)
 }
 
-/// Parse an expression or a named pair.
-fn item(p: &mut Parser) -> Option<CallArg> {
-    if p.eat_if(Token::Dots) {
-        return expr(p).map(CallArg::Spread);
+/// Parse an expression or a named pair, returning whether it's a spread or a
+/// named pair.
+fn item(p: &mut Parser) -> ParseResult<NodeKind> {
+    let marker = p.marker();
+    if p.eat_if(&NodeKind::Dots) {
+        marker.perform(p, NodeKind::Spread, expr)?;
+        return Ok(NodeKind::Spread);
     }
 
-    let first = expr(p)?;
-    if p.eat_if(Token::Colon) {
-        if let Expr::Ident(name) = first {
-            Some(CallArg::Named(Named { name: *name, expr: expr(p)? }))
-        } else {
-            p.error(first.span(), "expected identifier");
-            expr(p);
-            None
-        }
+    expr(p)?;
+
+    if p.at(&NodeKind::Colon) {
+        marker.perform(p, NodeKind::Named, |p| {
+            if let Some(NodeKind::Ident(_)) = marker.peek(p).map(|c| c.kind()) {
+                p.eat();
+                expr(p)
+            } else {
+                let error = NodeKind::Error(ErrorPos::Full, "expected identifier".into());
+                marker.end(p, error);
+                p.eat();
+                expr(p).ok();
+                Err(())
+            }
+        })?;
+
+        Ok(NodeKind::Named)
     } else {
-        Some(CallArg::Pos(first))
+        Ok(NodeKind::None)
     }
 }
 
 /// Convert a collection into an array, producing errors for anything other than
 /// expressions.
-fn array(p: &mut Parser, items: Vec<CallArg>, span: Span) -> Expr {
-    let iter = items.into_iter().filter_map(|item| match item {
-        CallArg::Pos(expr) => Some(expr),
-        CallArg::Named(_) => {
-            p.error(item.span(), "expected expression, found named pair");
-            None
-        }
-        CallArg::Spread(_) => {
-            p.error(item.span(), "spreading is not allowed here");
-            None
-        }
+fn array(p: &mut Parser, marker: Marker) {
+    marker.filter_children(p, |x| match x.kind() {
+        NodeKind::Named => Err("expected expression, found named pair"),
+        NodeKind::Spread => Err("spreading is not allowed here"),
+        _ => Ok(()),
     });
-    Expr::Array(Box::new(ArrayExpr { span, items: iter.collect() }))
+    marker.end(p, NodeKind::Array);
 }
 
 /// Convert a collection into a dictionary, producing errors for anything other
 /// than named pairs.
-fn dict(p: &mut Parser, items: Vec<CallArg>, span: Span) -> Expr {
-    let iter = items.into_iter().filter_map(|item| match item {
-        CallArg::Named(named) => Some(named),
-        CallArg::Pos(_) => {
-            p.error(item.span(), "expected named pair, found expression");
-            None
-        }
-        CallArg::Spread(_) => {
-            p.error(item.span(), "spreading is not allowed here");
-            None
-        }
+fn dict(p: &mut Parser, marker: Marker) {
+    marker.filter_children(p, |x| match x.kind() {
+        kind if kind.is_paren() => Ok(()),
+        NodeKind::Named | NodeKind::Comma | NodeKind::Colon => Ok(()),
+        NodeKind::Spread => Err("spreading is not allowed here"),
+        _ => Err("expected named pair, found expression"),
     });
-    Expr::Dict(Box::new(DictExpr { span, items: iter.collect() }))
+    marker.end(p, NodeKind::Dict);
 }
 
 /// Convert a collection into a list of parameters, producing errors for
 /// anything other than identifiers, spread operations and named pairs.
-fn params(p: &mut Parser, items: Vec<CallArg>) -> Vec<ClosureParam> {
-    let iter = items.into_iter().filter_map(|item| match item {
-        CallArg::Pos(Expr::Ident(ident)) => Some(ClosureParam::Pos(*ident)),
-        CallArg::Named(named) => Some(ClosureParam::Named(named)),
-        CallArg::Spread(Expr::Ident(ident)) => Some(ClosureParam::Sink(*ident)),
-        _ => {
-            p.error(item.span(), "expected identifier");
-            None
-        }
+fn params(p: &mut Parser, marker: Marker) {
+    marker.filter_children(p, |x| match x.kind() {
+        kind if kind.is_paren() => Ok(()),
+        NodeKind::Named | NodeKind::Comma | NodeKind::Ident(_) => Ok(()),
+        NodeKind::Spread
+            if matches!(
+                x.children().last().map(|child| child.kind()),
+                Some(&NodeKind::Ident(_))
+            ) =>
+        {
+            Ok(())
+        }
+        _ => Err("expected identifier"),
     });
-    iter.collect()
-}
-
-/// Convert a collection into a list of identifiers, producing errors for
-/// anything other than identifiers.
-fn idents(p: &mut Parser, items: Vec<CallArg>) -> Vec<Ident> {
-    let iter = items.into_iter().filter_map(|item| match item {
-        CallArg::Pos(Expr::Ident(ident)) => Some(*ident),
-        _ => {
-            p.error(item.span(), "expected identifier");
-            None
-        }
-    });
-    iter.collect()
+    marker.end(p, NodeKind::ClosureParams);
 }
 
 // Parse a template block: `[...]`.
-fn template(p: &mut Parser) -> Expr {
-    p.start_group(Group::Bracket, TokenMode::Markup);
-    let tree = markup(p);
-    let span = p.end_group();
-    Expr::Template(Box::new(TemplateExpr { span, body: tree }))
+fn template(p: &mut Parser) {
+    p.perform(NodeKind::Template, |p| {
+        p.start_group(Group::Bracket);
+        markup(p);
+        p.end_group();
+    });
 }
 
 /// Parse a code block: `{...}`.
-fn block(p: &mut Parser) -> Expr {
-    p.start_group(Group::Brace, TokenMode::Code);
-    let mut exprs = vec![];
-    while !p.eof() {
-        p.start_group(Group::Stmt, TokenMode::Code);
-        if let Some(expr) = expr(p) {
-            exprs.push(expr);
-            if !p.eof() {
-                p.expected_at(p.prev_end(), "semicolon or line break");
+fn block(p: &mut Parser) {
+    p.perform(NodeKind::Block, |p| {
+        p.start_group(Group::Brace);
+        while !p.eof() {
+            p.start_group(Group::Stmt);
+            if expr(p).is_ok() && !p.eof() {
+                p.expected_at("semicolon or line break");
             }
+            p.end_group();
+
+            // Forcefully skip over newlines since the group's contents can't.
+            p.eat_while(|t| matches!(t, NodeKind::Space(_)));
         }
         p.end_group();
-
-        // Forcefully skip over newlines since the group's contents can't.
-        p.eat_while(|t| matches!(t, Token::Space(_)));
-    }
-    let span = p.end_group();
-    Expr::Block(Box::new(BlockExpr { span, exprs }))
+    });
 }
 
 /// Parse a function call.
-fn call(p: &mut Parser, callee: Expr) -> Option<Expr> {
-    let mut args = match p.peek_direct() {
-        Some(Token::LeftParen) => args(p),
-        Some(Token::LeftBracket) => CallArgs {
-            span: Span::at(p.id(), callee.span().end),
-            items: vec![],
-        },
+fn call(p: &mut Parser, callee: Marker) -> ParseResult {
+    callee.perform(p, NodeKind::Call, |p| match p.peek_direct() {
+        Some(NodeKind::LeftParen | NodeKind::LeftBracket) => {
+            args(p, true);
+            Ok(())
+        }
         _ => {
-            p.expected_at(p.prev_end(), "argument list");
-            return None;
+            p.expected_at("argument list");
+            Err(())
         }
-    };
-
-    while p.peek_direct() == Some(Token::LeftBracket) {
-        let body = template(p);
-        args.items.push(CallArg::Pos(body));
-    }
-
-    Some(Expr::Call(Box::new(CallExpr {
-        span: p.span_from(callee.span().start),
-        callee,
-        args,
-    })))
+    })
 }
 
 /// Parse the arguments to a function call.
-fn args(p: &mut Parser) -> CallArgs {
-    p.start_group(Group::Paren, TokenMode::Code);
-    let items = collection(p).0;
-    let span = p.end_group();
-    CallArgs { span, items }
+fn args(p: &mut Parser, allow_template: bool) {
+    p.perform(NodeKind::CallArgs, |p| {
+        if !allow_template || p.peek_direct() == Some(&NodeKind::LeftParen) {
+            p.start_group(Group::Paren);
+            collection(p);
+            p.end_group();
+        }
+
+        while allow_template && p.peek_direct() == Some(&NodeKind::LeftBracket) {
+            template(p);
+        }
+    })
 }
 
 /// Parse a with expression.
-fn with_expr(p: &mut Parser, callee: Expr) -> Option<Expr> {
-    if p.peek() == Some(Token::LeftParen) {
-        Some(Expr::With(Box::new(WithExpr {
-            span: p.span_from(callee.span().start),
-            callee,
-            args: args(p),
-        })))
-    } else {
-        p.expected("argument list");
-        None
-    }
+fn with_expr(p: &mut Parser, marker: Marker) -> ParseResult {
+    marker.perform(p, NodeKind::WithExpr, |p| {
+        p.eat_assert(&NodeKind::With);
+
+        if p.at(&NodeKind::LeftParen) {
+            args(p, false);
+            Ok(())
+        } else {
+            p.expected("argument list");
+            Err(())
+        }
+    })
 }
 
 /// Parse a let expression.
-fn let_expr(p: &mut Parser) -> Option<Expr> {
-    let start = p.next_start();
-    p.eat_assert(Token::Let);
+fn let_expr(p: &mut Parser) -> ParseResult {
+    p.perform(NodeKind::LetExpr, |p| {
+        p.eat_assert(&NodeKind::Let);
 
-    let mut output = None;
-    if let Some(binding) = ident(p) {
-        let mut init = None;
+        let marker = p.marker();
+        ident(p)?;
 
-        if p.eat_if(Token::With) {
-            init = with_expr(p, Expr::Ident(Box::new(binding.clone())));
+        if p.at(&NodeKind::With) {
+            with_expr(p, marker)?;
         } else {
             // If a parenthesis follows, this is a function definition.
-            let mut maybe_params = None;
-            if p.peek_direct() == Some(Token::LeftParen) {
-                p.start_group(Group::Paren, TokenMode::Code);
-                let items = collection(p).0;
-                maybe_params = Some(params(p, items));
+            let has_params = p.peek_direct() == Some(&NodeKind::LeftParen);
+            if has_params {
+                let marker = p.marker();
+                p.start_group(Group::Paren);
+                collection(p);
                 p.end_group();
+                params(p, marker);
             }
 
-            if p.eat_if(Token::Eq) {
-                init = expr(p);
-            } else if maybe_params.is_some() {
+            if p.eat_if(&NodeKind::Eq) {
+                expr(p)?;
+            } else if has_params {
                 // Function definitions must have a body.
-                p.expected_at(p.prev_end(), "body");
+                p.expected_at("body");
             }
 
             // Rewrite into a closure expression if it's a function definition.
-            if let Some(params) = maybe_params {
-                let body = init?;
-                init = Some(Expr::Closure(Box::new(ClosureExpr {
-                    span: binding.span.join(body.span()),
-                    name: Some(binding.clone()),
-                    params,
-                    body: Rc::new(body),
-                })));
+            if has_params {
+                marker.end(p, NodeKind::Closure);
             }
         }
 
-        output = Some(Expr::Let(Box::new(LetExpr {
-            span: p.span_from(start),
-            binding,
-            init,
-        })));
-    }
-
-    output
+        Ok(())
+    })
 }
 
 /// Parse an if expresion.
-fn if_expr(p: &mut Parser) -> Option<Expr> {
-    let start = p.next_start();
-    p.eat_assert(Token::If);
-
-    let mut output = None;
-    if let Some(condition) = expr(p) {
-        if let Some(if_body) = body(p) {
-            let mut else_body = None;
-            if p.eat_if(Token::Else) {
-                if p.peek() == Some(Token::If) {
-                    else_body = if_expr(p);
-                } else {
-                    else_body = body(p);
-                }
-            }
+fn if_expr(p: &mut Parser) -> ParseResult {
+    p.perform(NodeKind::IfExpr, |p| {
+        p.eat_assert(&NodeKind::If);
+
+        expr(p)?;
+        body(p)?;
 
-            output = Some(Expr::If(Box::new(IfExpr {
-                span: p.span_from(start),
-                condition,
-                if_body,
-                else_body,
-            })));
+        if p.eat_if(&NodeKind::Else) {
+            if p.at(&NodeKind::If) {
+                if_expr(p)?;
+            } else {
+                body(p)?;
+            }
         }
-    }
 
-    output
+        Ok(())
+    })
 }
 
 /// Parse a while expresion.
-fn while_expr(p: &mut Parser) -> Option<Expr> {
-    let start = p.next_start();
-    p.eat_assert(Token::While);
-
-    let mut output = None;
-    if let Some(condition) = expr(p) {
-        if let Some(body) = body(p) {
-            output = Some(Expr::While(Box::new(WhileExpr {
-                span: p.span_from(start),
-                condition,
-                body,
-            })));
-        }
-    }
-
-    output
+fn while_expr(p: &mut Parser) -> ParseResult {
+    p.perform(NodeKind::WhileExpr, |p| {
+        p.eat_assert(&NodeKind::While);
+        expr(p)?;
+        body(p)?;
+        Ok(())
+    })
 }
 
 /// Parse a for expression.
-fn for_expr(p: &mut Parser) -> Option<Expr> {
-    let start = p.next_start();
-    p.eat_assert(Token::For);
-
-    let mut output = None;
-    if let Some(pattern) = for_pattern(p) {
-        if p.eat_expect(Token::In) {
-            if let Some(iter) = expr(p) {
-                if let Some(body) = body(p) {
-                    output = Some(Expr::For(Box::new(ForExpr {
-                        span: p.span_from(start),
-                        pattern,
-                        iter,
-                        body,
-                    })));
-                }
-            }
-        }
-    }
-
-    output
+fn for_expr(p: &mut Parser) -> ParseResult {
+    p.perform(NodeKind::ForExpr, |p| {
+        p.eat_assert(&NodeKind::For);
+        for_pattern(p)?;
+        p.eat_expect(&NodeKind::In)?;
+        expr(p)?;
+        body(p)?;
+        Ok(())
+    })
 }
 
 /// Parse a for loop pattern.
-fn for_pattern(p: &mut Parser) -> Option<ForPattern> {
-    let first = ident(p)?;
-    if p.eat_if(Token::Comma) {
-        if let Some(second) = ident(p) {
-            return Some(ForPattern::KeyValue(first, second));
+fn for_pattern(p: &mut Parser) -> ParseResult {
+    p.perform(NodeKind::ForPattern, |p| {
+        ident(p)?;
+        if p.eat_if(&NodeKind::Comma) {
+            ident(p)?;
         }
-    }
-    Some(ForPattern::Value(first))
+        Ok(())
+    })
 }
 
 /// Parse an import expression.
-fn import_expr(p: &mut Parser) -> Option<Expr> {
-    let start = p.next_start();
-    p.eat_assert(Token::Import);
+fn import_expr(p: &mut Parser) -> ParseResult {
+    p.perform(NodeKind::ImportExpr, |p| {
+        p.eat_assert(&NodeKind::Import);
+
+        if !p.eat_if(&NodeKind::Star) {
+            // This is the list of identifiers scenario.
+            p.perform(NodeKind::ImportItems, |p| {
+                p.start_group(Group::Imports);
+                let marker = p.marker();
+                let items = collection(p).1;
+                if items == 0 {
+                    p.expected_at("import items");
+                }
+                p.end_group();
 
-    let imports = if p.eat_if(Token::Star) {
-        // This is the wildcard scenario.
-        Imports::Wildcard
-    } else {
-        // This is the list of identifiers scenario.
-        p.start_group(Group::Imports, TokenMode::Code);
-        let items = collection(p).0;
-        if items.is_empty() {
-            p.expected_at(p.prev_end(), "import items");
-        }
-        p.end_group();
-        Imports::Idents(idents(p, items))
-    };
+                marker.filter_children(p, |n| match n.kind() {
+                    NodeKind::Ident(_) | NodeKind::Comma => Ok(()),
+                    _ => Err("expected identifier"),
+                });
+            });
+        };
 
-    let mut output = None;
-    if p.eat_expect(Token::From) {
-        if let Some(path) = expr(p) {
-            output = Some(Expr::Import(Box::new(ImportExpr {
-                span: p.span_from(start),
-                imports,
-                path,
-            })));
-        }
-    }
+        p.eat_expect(&NodeKind::From)?;
+        expr(p)?;
 
-    output
+        Ok(())
+    })
 }
 
 /// Parse an include expression.
-fn include_expr(p: &mut Parser) -> Option<Expr> {
-    let start = p.next_start();
-    p.eat_assert(Token::Include);
-
-    expr(p).map(|path| {
-        Expr::Include(Box::new(IncludeExpr { span: p.span_from(start), path }))
+fn include_expr(p: &mut Parser) -> ParseResult {
+    p.perform(NodeKind::IncludeExpr, |p| {
+        p.eat_assert(&NodeKind::Include);
+        expr(p)?;
+        Ok(())
     })
 }
 
 /// Parse an identifier.
-fn ident(p: &mut Parser) -> Option<Ident> {
-    if let Some(Token::Ident(string)) = p.peek() {
-        Some(Ident {
-            span: p.eat_span(),
-            string: string.into(),
-        })
-    } else {
-        p.expected("identifier");
-        None
+fn ident(p: &mut Parser) -> ParseResult {
+    match p.peek() {
+        Some(NodeKind::Ident(_)) => {
+            p.eat();
+            Ok(())
+        }
+        _ => {
+            p.expected("identifier");
+            Err(())
+        }
     }
 }
 
 /// Parse a control flow body.
-fn body(p: &mut Parser) -> Option<Expr> {
+fn body(p: &mut Parser) -> ParseResult {
     match p.peek() {
-        Some(Token::LeftBracket) => Some(template(p)),
-        Some(Token::LeftBrace) => Some(block(p)),
+        Some(NodeKind::LeftBracket) => template(p),
+        Some(NodeKind::LeftBrace) => block(p),
         _ => {
-            p.expected_at(p.prev_end(), "body");
-            None
+            p.expected_at("body");
+            return Err(());
         }
     }
+    Ok(())
 }
diff --git a/src/parse/parser.rs b/src/parse/parser.rs
index 347d6f71..1c4c2a5c 100644
--- a/src/parse/parser.rs
+++ b/src/parse/parser.rs
@@ -1,250 +1,216 @@
-use std::ops::Range;
+use std::mem;
 
 use super::{TokenMode, Tokens};
-use crate::diag::Error;
-use crate::source::{SourceFile, SourceId};
-use crate::syntax::{IntoSpan, Pos, Span, Token};
+use crate::syntax::{ErrorPos, Green, GreenData, GreenNode, NodeKind};
+use crate::util::EcoString;
+
+/// Allows parser methods to use the try operator. Not exposed as the parser
+/// recovers from all errors.
+pub(crate) type ParseResult<T = ()> = Result<T, ()>;
 
 /// A convenient token-based parser.
 pub struct Parser<'s> {
-    /// The parsed file.
-    source: &'s SourceFile,
-    /// Parsing errors.
-    errors: Vec<Error>,
     /// An iterator over the source tokens.
     tokens: Tokens<'s>,
+    /// Whether we are at the end of the file or of a group.
+    eof: bool,
+    /// The current token.
+    current: Option<NodeKind>,
+    /// The end byte index of the last non-trivia token.
+    prev_end: usize,
+    /// The start byte index of the peeked token.
+    current_start: usize,
     /// The stack of open groups.
     groups: Vec<GroupEntry>,
-    /// The next token.
-    next: Option<Token<'s>>,
-    /// The peeked token.
-    /// (Same as `next` except if we are at the end of group, then `None`).
-    peeked: Option<Token<'s>>,
-    /// The end index of the last (non-whitespace if in code mode) token.
-    prev_end: usize,
-    /// The start index of the peeked token.
-    next_start: usize,
-}
-
-/// A logical group of tokens, e.g. `[...]`.
-struct GroupEntry {
-    /// The kind of group this is. This decides which tokens will end the group.
-    /// For example, a [`Group::Paren`] will be ended by
-    /// [`Token::RightParen`].
-    pub kind: Group,
-    /// The start index of the group. Used by `Parser::end_group` to return the
-    /// group's full span.
-    pub start: usize,
-    /// The mode the parser was in _before_ the group started (to which we go
-    /// back once the group ends).
-    pub prev_mode: TokenMode,
-}
-
-/// A group, confined by optional start and end delimiters.
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
-pub enum Group {
-    /// A parenthesized group: `(...)`.
-    Paren,
-    /// A bracketed group: `[...]`.
-    Bracket,
-    /// A curly-braced group: `{...}`.
-    Brace,
-    /// A group ended by a semicolon or a line break: `;`, `\n`.
-    Stmt,
-    /// A group for a single expression, ended by a line break.
-    Expr,
-    /// A group for import items, ended by a semicolon, line break or `from`.
-    Imports,
+    /// The children of the currently built node.
+    children: Vec<Green>,
 }
 
 impl<'s> Parser<'s> {
     /// Create a new parser for the source string.
-    pub fn new(source: &'s SourceFile) -> Self {
-        let mut tokens = Tokens::new(source.src(), TokenMode::Markup);
-        let next = tokens.next();
+    pub fn new(src: &'s str) -> Self {
+        let mut tokens = Tokens::new(src, TokenMode::Markup);
+        let current = tokens.next();
         Self {
-            source,
-            errors: vec![],
             tokens,
-            groups: vec![],
-            next,
-            peeked: next,
+            eof: current.is_none(),
+            current,
             prev_end: 0,
-            next_start: 0,
+            current_start: 0,
+            groups: vec![],
+            children: vec![],
         }
     }
 
-    /// Finish parsing and return all errors.
-    pub fn finish(self) -> Vec<Error> {
-        self.errors
+    /// End the parsing process and return the last child.
+    pub fn finish(self) -> Vec<Green> {
+        self.children
     }
 
-    /// The id of the parsed source file.
-    pub fn id(&self) -> SourceId {
-        self.source.id()
+    /// Create a new marker.
+    pub fn marker(&mut self) -> Marker {
+        Marker(self.children.len())
     }
 
-    /// Whether the end of the source string or group is reached.
-    pub fn eof(&self) -> bool {
-        self.peek().is_none()
+    /// Create a markup right before the trailing trivia.
+    pub fn trivia_start(&self) -> Marker {
+        let count = self
+            .children
+            .iter()
+            .rev()
+            .take_while(|node| self.is_trivia(node.kind()))
+            .count();
+        Marker(self.children.len() - count)
     }
 
-    /// Consume the next token.
-    pub fn eat(&mut self) -> Option<Token<'s>> {
-        let token = self.peek()?;
-        self.bump();
-        Some(token)
+    /// Perform a subparse that wraps its result in a node with the given kind.
+    pub fn perform<F, T>(&mut self, kind: NodeKind, f: F) -> T
+    where
+        F: FnOnce(&mut Self) -> T,
+    {
+        let prev = mem::take(&mut self.children);
+        let output = f(self);
+        let until = self.trivia_start();
+        let mut children = mem::replace(&mut self.children, prev);
+
+        if self.tokens.mode() == TokenMode::Code {
+            // Trailing trivia should not be wrapped into the new node.
+            let idx = self.children.len();
+            self.children.push(Green::default());
+            self.children.extend(children.drain(until.0 ..));
+            self.children[idx] = GreenNode::with_children(kind, children).into();
+        } else {
+            self.children.push(GreenNode::with_children(kind, children).into());
+        }
+
+        output
     }
 
-    /// Eat the next token and return its source range.
-    pub fn eat_span(&mut self) -> Span {
-        let start = self.next_start();
-        self.eat();
-        Span::new(self.id(), start, self.prev_end())
+    /// Whether the end of the source string or group is reached.
+    pub fn eof(&self) -> bool {
+        self.eof
     }
 
-    /// Consume the next token if it is the given one.
-    pub fn eat_if(&mut self, t: Token) -> bool {
-        if self.peek() == Some(t) {
-            self.bump();
-            true
-        } else {
-            false
+    /// Consume the current token and also trailing trivia.
+    pub fn eat(&mut self) {
+        self.prev_end = self.tokens.index();
+        self.bump();
+
+        if self.tokens.mode() == TokenMode::Code {
+            // Skip whitespace and comments.
+            while self.current.as_ref().map_or(false, |x| self.is_trivia(x)) {
+                self.bump();
+            }
         }
+
+        self.repeek();
     }
 
-    /// Consume the next token if the closure maps it a to `Some`-variant.
-    pub fn eat_map<T, F>(&mut self, f: F) -> Option<T>
-    where
-        F: FnOnce(Token<'s>) -> Option<T>,
-    {
-        let token = self.peek()?;
-        let mapped = f(token);
-        if mapped.is_some() {
-            self.bump();
+    /// Eat if the current token it is the given one.
+    pub fn eat_if(&mut self, t: &NodeKind) -> bool {
+        let at = self.at(t);
+        if at {
+            self.eat();
         }
-        mapped
+        at
     }
 
-    /// Consume the next token if it is the given one and produce an error if
-    /// not.
-    pub fn eat_expect(&mut self, t: Token) -> bool {
+    /// Eat if the current token is the given one and produce an error if not.
+    pub fn eat_expect(&mut self, t: &NodeKind) -> ParseResult {
         let eaten = self.eat_if(t);
         if !eaten {
-            self.expected_at(self.prev_end(), t.name());
+            self.expected_at(t.as_str());
         }
-        eaten
+        if eaten { Ok(()) } else { Err(()) }
     }
 
-    /// Consume the next token, debug-asserting that it is one of the given ones.
-    pub fn eat_assert(&mut self, t: Token) {
-        let next = self.eat();
-        debug_assert_eq!(next, Some(t));
+    /// Eat, debug-asserting that the token is the given one.
+    pub fn eat_assert(&mut self, t: &NodeKind) {
+        debug_assert_eq!(self.peek(), Some(t));
+        self.eat();
     }
 
-    /// Consume tokens while the condition is true.
+    /// Eat tokens while the condition is true.
     pub fn eat_while<F>(&mut self, mut f: F)
     where
-        F: FnMut(Token<'s>) -> bool,
+        F: FnMut(&NodeKind) -> bool,
     {
         while self.peek().map_or(false, |t| f(t)) {
             self.eat();
         }
     }
 
-    /// Peek at the next token without consuming it.
-    pub fn peek(&self) -> Option<Token<'s>> {
-        self.peeked
+    /// Eat the current token, but change its type.
+    pub fn convert(&mut self, kind: NodeKind) {
+        let marker = self.marker();
+        self.eat();
+        marker.convert(self, kind);
     }
 
-    /// Peek at the next token if it follows immediately after the last one
-    /// without any whitespace in between.
-    pub fn peek_direct(&self) -> Option<Token<'s>> {
-        if self.next_start() == self.prev_end() {
-            self.peeked
-        } else {
-            None
-        }
+    /// Whether the current token is of the given type.
+    pub fn at(&self, kind: &NodeKind) -> bool {
+        self.peek() == Some(kind)
     }
 
-    /// Peek at the span of the next token.
-    ///
-    /// Has length zero if `peek()` returns `None`.
-    pub fn peek_span(&self) -> Span {
-        Span::new(self.id(), self.next_start(), self.next_end())
+    /// Peek at the current token without consuming it.
+    pub fn peek(&self) -> Option<&NodeKind> {
+        if self.eof { None } else { self.current.as_ref() }
     }
 
-    /// Peek at the source of the next token.
-    pub fn peek_src(&self) -> &'s str {
-        self.get(self.next_start() .. self.next_end())
+    /// Peek at the current token, if it follows immediately after the last one
+    /// without any trivia in between.
+    pub fn peek_direct(&self) -> Option<&NodeKind> {
+        if self.prev_end() == self.current_start() {
+            self.peek()
+        } else {
+            None
+        }
     }
 
-    /// Checks whether the next token fulfills a condition.
-    ///
-    /// Returns `false` if there is no next token.
-    pub fn check<F>(&self, f: F) -> bool
-    where
-        F: FnOnce(Token<'s>) -> bool,
-    {
-        self.peek().map_or(false, f)
+    /// Peek at the source of the current token.
+    pub fn peek_src(&self) -> &'s str {
+        self.tokens.scanner().get(self.current_start() .. self.current_end())
     }
 
-    /// The byte index at which the last token ended.
-    ///
-    /// Refers to the end of the last _non-whitespace_ token in code mode.
+    /// The byte index at which the last non-trivia token ended.
     pub fn prev_end(&self) -> usize {
         self.prev_end
     }
 
-    /// The byte index at which the next token starts.
-    pub fn next_start(&self) -> usize {
-        self.next_start
+    /// The byte index at which the current token starts.
+    pub fn current_start(&self) -> usize {
+        self.current_start
     }
 
-    /// The byte index at which the next token will end.
-    ///
-    /// Is the same as [`next_start()`][Self::next_start] if `peek()` returns
-    /// `None`.
-    pub fn next_end(&self) -> usize {
+    /// The byte index at which the current token ends.
+    pub fn current_end(&self) -> usize {
         self.tokens.index()
     }
 
     /// Determine the column index for the given byte index.
     pub fn column(&self, index: usize) -> usize {
-        self.source.byte_to_column(index).unwrap()
-    }
-
-    /// Slice out part of the source string.
-    pub fn get(&self, range: Range<usize>) -> &'s str {
-        self.source.get(range).unwrap()
-    }
-
-    /// The span from `start` to [`self.prev_end()`](Self::prev_end).
-    pub fn span_from(&self, start: impl Into<Pos>) -> Span {
-        Span::new(self.id(), start, self.prev_end())
+        self.tokens.scanner().column(index)
     }
 
     /// Continue parsing in a group.
     ///
     /// When the end delimiter of the group is reached, all subsequent calls to
-    /// `eat()` and `peek()` return `None`. Parsing can only continue with
-    /// a matching call to `end_group`.
+    /// `peek()` return `None`. Parsing can only continue with a matching call
+    /// to `end_group`.
     ///
-    /// This panics if the next token does not start the given group.
-    pub fn start_group(&mut self, kind: Group, mode: TokenMode) {
-        self.groups.push(GroupEntry {
-            kind,
-            start: self.next_start(),
-            prev_mode: self.tokens.mode(),
+    /// This panics if the current token does not start the given group.
+    pub fn start_group(&mut self, kind: Group) {
+        self.groups.push(GroupEntry { kind, prev_mode: self.tokens.mode() });
+        self.tokens.set_mode(match kind {
+            Group::Bracket => TokenMode::Markup,
+            _ => TokenMode::Code,
         });
 
-        self.tokens.set_mode(mode);
         self.repeek();
-
         match kind {
-            Group::Paren => self.eat_assert(Token::LeftParen),
-            Group::Bracket => self.eat_assert(Token::LeftBracket),
-            Group::Brace => self.eat_assert(Token::LeftBrace),
+            Group::Paren => self.eat_assert(&NodeKind::LeftParen),
+            Group::Bracket => self.eat_assert(&NodeKind::LeftBracket),
+            Group::Brace => self.eat_assert(&NodeKind::LeftBrace),
             Group::Stmt => {}
             Group::Expr => {}
             Group::Imports => {}
@@ -254,130 +220,228 @@ impl<'s> Parser<'s> {
     /// End the parsing of a group.
     ///
     /// This panics if no group was started.
-    pub fn end_group(&mut self) -> Span {
-        let prev_mode = self.tokens.mode();
+    pub fn end_group(&mut self) {
+        let group_mode = self.tokens.mode();
         let group = self.groups.pop().expect("no started group");
         self.tokens.set_mode(group.prev_mode);
         self.repeek();
 
-        let mut rescan = self.tokens.mode() != prev_mode;
+        let mut rescan = self.tokens.mode() != group_mode;
 
         // Eat the end delimiter if there is one.
         if let Some((end, required)) = match group.kind {
-            Group::Paren => Some((Token::RightParen, true)),
-            Group::Bracket => Some((Token::RightBracket, true)),
-            Group::Brace => Some((Token::RightBrace, true)),
-            Group::Stmt => Some((Token::Semicolon, false)),
+            Group::Paren => Some((NodeKind::RightParen, true)),
+            Group::Bracket => Some((NodeKind::RightBracket, true)),
+            Group::Brace => Some((NodeKind::RightBrace, true)),
+            Group::Stmt => Some((NodeKind::Semicolon, false)),
             Group::Expr => None,
             Group::Imports => None,
         } {
-            if self.next == Some(end) {
+            if self.current.as_ref() == Some(&end) {
                 // Bump the delimeter and return. No need to rescan in this case.
-                self.bump();
+                self.eat();
                 rescan = false;
             } else if required {
-                self.error(
-                    self.next_start() .. self.next_start(),
-                    format!("expected {}", end.name()),
-                );
+                self.push_error(format!("expected {}", end));
             }
         }
 
         // Rescan the peeked token if the mode changed.
         if rescan {
+            if group_mode == TokenMode::Code {
+                self.children.truncate(self.trivia_start().0);
+            }
+
             self.tokens.jump(self.prev_end());
-            self.bump();
+            self.prev_end = self.tokens.index();
+            self.current_start = self.tokens.index();
+            self.current = self.tokens.next();
+            self.repeek();
         }
+    }
 
-        Span::new(self.id(), group.start, self.prev_end())
+    /// Low-level bump that consumes exactly one token without special trivia
+    /// handling.
+    fn bump(&mut self) {
+        let kind = self.current.take().unwrap();
+        let len = self.tokens.index() - self.current_start;
+        self.children.push(GreenData::new(kind, len).into());
+        self.current_start = self.tokens.index();
+        self.current = self.tokens.next();
     }
 
-    /// Add an error with location and message.
-    pub fn error(&mut self, span: impl IntoSpan, message: impl Into<String>) {
-        self.errors.push(Error::new(span.into_span(self.id()), message));
+    /// Take another look at the current token to recheck whether it ends a
+    /// group.
+    fn repeek(&mut self) {
+        self.eof = match &self.current {
+            Some(NodeKind::RightParen) => self.inside(Group::Paren),
+            Some(NodeKind::RightBracket) => self.inside(Group::Bracket),
+            Some(NodeKind::RightBrace) => self.inside(Group::Brace),
+            Some(NodeKind::Semicolon) => self.inside(Group::Stmt),
+            Some(NodeKind::From) => self.inside(Group::Imports),
+            Some(NodeKind::Space(n)) => *n >= 1 && self.stop_at_newline(),
+            Some(_) => false,
+            None => true,
+        };
     }
 
-    /// Add an error that `what` was expected at the given span.
-    pub fn expected_at(&mut self, span: impl IntoSpan, what: &str) {
-        self.error(span, format!("expected {}", what));
+    /// Returns whether the given type can be skipped over.
+    fn is_trivia(&self, token: &NodeKind) -> bool {
+        Self::is_trivia_ext(token, self.stop_at_newline())
     }
 
-    /// Eat the next token and add an error that it is not the expected `thing`.
-    pub fn expected(&mut self, what: &str) {
-        let before = self.next_start();
-        if let Some(found) = self.eat() {
-            let after = self.prev_end();
-            self.error(
-                before .. after,
-                format!("expected {}, found {}", what, found.name()),
-            );
-        } else {
-            self.expected_at(self.next_start(), what);
+    /// Returns whether the given type can be skipped over given the current
+    /// newline mode.
+    fn is_trivia_ext(token: &NodeKind, stop_at_newline: bool) -> bool {
+        match token {
+            NodeKind::Space(n) => *n == 0 || !stop_at_newline,
+            NodeKind::LineComment => true,
+            NodeKind::BlockComment => true,
+            _ => false,
         }
     }
 
-    /// Eat the next token and add an error that it is unexpected.
+    /// Whether the active group must end at a newline.
+    fn stop_at_newline(&self) -> bool {
+        matches!(
+            self.groups.last().map(|group| group.kind),
+            Some(Group::Stmt | Group::Expr | Group::Imports)
+        )
+    }
+
+    /// Whether we are inside the given group.
+    fn inside(&self, kind: Group) -> bool {
+        self.groups.iter().any(|g| g.kind == kind)
+    }
+}
+
+/// Error handling.
+impl Parser<'_> {
+    /// Push an error into the children list.
+    pub fn push_error(&mut self, msg: impl Into<EcoString>) {
+        let error = NodeKind::Error(ErrorPos::Full, msg.into());
+        self.children.push(GreenData::new(error, 0).into());
+    }
+
+    /// Eat the current token and add an error that it is unexpected.
     pub fn unexpected(&mut self) {
-        let before = self.next_start();
-        if let Some(found) = self.eat() {
-            let after = self.prev_end();
-            self.error(before .. after, format!("unexpected {}", found.name()));
+        match self.peek() {
+            Some(found) => {
+                let msg = format!("unexpected {}", found);
+                let error = NodeKind::Error(ErrorPos::Full, msg.into());
+                self.perform(error, Self::eat);
+            }
+            None => self.push_error("unexpected end of file"),
         }
     }
 
-    /// Move to the next token.
-    fn bump(&mut self) {
-        self.prev_end = self.tokens.index().into();
-        self.next_start = self.tokens.index().into();
-        self.next = self.tokens.next();
-
-        if self.tokens.mode() == TokenMode::Code {
-            // Skip whitespace and comments.
-            while match self.next {
-                Some(Token::Space(n)) => n < 1 || !self.stop_at_newline(),
-                Some(Token::LineComment(_)) => true,
-                Some(Token::BlockComment(_)) => true,
-                _ => false,
-            } {
-                self.next_start = self.tokens.index().into();
-                self.next = self.tokens.next();
+    /// Eat the current token and add an error that it is not the expected `thing`.
+    pub fn expected(&mut self, thing: &str) {
+        match self.peek() {
+            Some(found) => {
+                let msg = format!("expected {}, found {}", thing, found);
+                let error = NodeKind::Error(ErrorPos::Full, msg.into());
+                self.perform(error, Self::eat);
             }
+            None => self.expected_at(thing),
         }
+    }
 
-        self.repeek();
+    /// Add an error that the `thing` was expected at the end of the last
+    /// non-trivia token.
+    pub fn expected_at(&mut self, thing: &str) {
+        self.trivia_start().expected(self, thing);
     }
+}
 
-    /// Take another look at the next token to recheck whether it ends a group.
-    fn repeek(&mut self) {
-        self.peeked = self.next;
-        let token = match self.next {
-            Some(token) => token,
-            None => return,
-        };
+/// A marker that indicates where a node may start.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub struct Marker(usize);
 
-        if match token {
-            Token::RightParen => self.inside(Group::Paren),
-            Token::RightBracket => self.inside(Group::Bracket),
-            Token::RightBrace => self.inside(Group::Brace),
-            Token::Semicolon => self.inside(Group::Stmt),
-            Token::From => self.inside(Group::Imports),
-            Token::Space(n) => n >= 1 && self.stop_at_newline(),
-            _ => false,
-        } {
-            self.peeked = None;
+impl Marker {
+    /// Perform a subparse that wraps all children after the marker in a node
+    /// with the given kind.
+    pub fn perform<T, F>(self, p: &mut Parser, kind: NodeKind, f: F) -> T
+    where
+        F: FnOnce(&mut Parser) -> T,
+    {
+        let success = f(p);
+        self.end(p, kind);
+        success
+    }
+
+    /// Wrap all children after the marker (excluding trailing trivia) in a node
+    /// with the given `kind`.
+    pub fn end(self, p: &mut Parser, kind: NodeKind) {
+        let until = p.trivia_start();
+        let children = p.children.drain(self.0 .. until.0).collect();
+        p.children
+            .insert(self.0, GreenNode::with_children(kind, children).into());
+    }
+
+    /// Wrap all children that do not fulfill the predicate in error nodes.
+    pub fn filter_children<F>(self, p: &mut Parser, f: F)
+    where
+        F: Fn(&Green) -> Result<(), &'static str>,
+    {
+        for child in &mut p.children[self.0 ..] {
+            if (p.tokens.mode() == TokenMode::Markup
+                || !Parser::is_trivia_ext(child.kind(), false))
+                && !child.kind().is_error()
+            {
+                if let Err(msg) = f(child) {
+                    let error = NodeKind::Error(ErrorPos::Full, msg.into());
+                    let inner = mem::take(child);
+                    *child = GreenNode::with_child(error, inner).into();
+                }
+            }
         }
     }
 
-    /// Whether the active group ends at a newline.
-    fn stop_at_newline(&self) -> bool {
-        matches!(
-            self.groups.last().map(|group| group.kind),
-            Some(Group::Stmt | Group::Expr | Group::Imports)
-        )
+    /// Insert an error message that `what` was expected at the marker position.
+    pub fn expected(self, p: &mut Parser, what: &str) {
+        let msg = format!("expected {}", what);
+        let error = NodeKind::Error(ErrorPos::Full, msg.into());
+        p.children.insert(self.0, GreenData::new(error, 0).into());
     }
 
-    /// Whether we are inside the given group.
-    fn inside(&self, kind: Group) -> bool {
-        self.groups.iter().any(|g| g.kind == kind)
+    /// Peek at the child directly after the marker.
+    pub fn peek<'a>(self, p: &'a Parser) -> Option<&'a Green> {
+        p.children.get(self.0)
     }
+
+    /// Convert the child directly after marker.
+    pub fn convert(self, p: &mut Parser, kind: NodeKind) {
+        if let Some(child) = p.children.get_mut(self.0) {
+            child.convert(kind);
+        }
+    }
+}
+
+/// A logical group of tokens, e.g. `[...]`.
+struct GroupEntry {
+    /// The kind of group this is. This decides which tokens will end the group.
+    /// For example, a [`Group::Paren`] will be ended by
+    /// [`Token::RightParen`].
+    pub kind: Group,
+    /// The mode the parser was in _before_ the group started (to which we go
+    /// back once the group ends).
+    pub prev_mode: TokenMode,
+}
+
+/// A group, confined by optional start and end delimiters.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum Group {
+    /// A bracketed group: `[...]`.
+    Bracket,
+    /// A curly-braced group: `{...}`.
+    Brace,
+    /// A parenthesized group: `(...)`.
+    Paren,
+    /// A group ended by a semicolon or a line break: `;`, `\n`.
+    Stmt,
+    /// A group for a single expression, ended by a line break.
+    Expr,
+    /// A group for import items, ended by a semicolon, line break or `from`.
+    Imports,
 }
diff --git a/src/parse/resolve.rs b/src/parse/resolve.rs
index 1b323847..e15ae339 100644
--- a/src/parse/resolve.rs
+++ b/src/parse/resolve.rs
@@ -1,5 +1,5 @@
-use super::{is_newline, Scanner};
-use crate::syntax::{Ident, RawNode, Span};
+use super::{is_ident, is_newline, Scanner};
+use crate::syntax::ast::RawNode;
 use crate::util::EcoString;
 
 /// Resolve all escape sequences in a string.
@@ -25,11 +25,9 @@ pub fn resolve_string(string: &str) -> EcoString {
                 let sequence = s.eat_while(|c| c.is_ascii_hexdigit());
                 let _terminated = s.eat_if('}');
 
-                if let Some(c) = resolve_hex(sequence) {
-                    out.push(c);
-                } else {
-                    // TODO: Feedback that unicode escape sequence is wrong.
-                    out.push_str(s.eaten_from(start));
+                match resolve_hex(sequence) {
+                    Some(c) => out.push(c),
+                    None => out.push_str(s.eaten_from(start)),
                 }
             }
 
@@ -48,19 +46,17 @@ pub fn resolve_hex(sequence: &str) -> Option<char> {
 }
 
 /// Resolve the language tag and trims the raw text.
-pub fn resolve_raw(span: Span, column: usize, backticks: usize, text: &str) -> RawNode {
+pub fn resolve_raw(column: usize, backticks: usize, text: &str) -> RawNode {
     if backticks > 1 {
         let (tag, inner) = split_at_lang_tag(text);
         let (text, block) = trim_and_split_raw(column, inner);
         RawNode {
-            span,
-            lang: Ident::new(tag, span.with_end(span.start + tag.len())),
+            lang: is_ident(tag).then(|| tag.into()),
             text: text.into(),
             block,
         }
     } else {
         RawNode {
-            span,
             lang: None,
             text: split_lines(text).join("\n").into(),
             block: false,
@@ -140,7 +136,6 @@ fn split_lines(text: &str) -> Vec<&str> {
 #[cfg(test)]
 #[rustfmt::skip]
 mod tests {
-    use crate::syntax::Span;
     use super::*;
 
     #[test]
@@ -190,7 +185,7 @@ mod tests {
             text: &str,
             block: bool,
         ) {
-            let node = resolve_raw(Span::detached(), column, backticks, raw);
+            let node = resolve_raw(column, backticks, raw);
             assert_eq!(node.lang.as_deref(), lang);
             assert_eq!(node.text, text);
             assert_eq!(node.block, block);
diff --git a/src/parse/scanner.rs b/src/parse/scanner.rs
index 8e3e4278..ea06a2e0 100644
--- a/src/parse/scanner.rs
+++ b/src/parse/scanner.rs
@@ -1,5 +1,7 @@
 use std::slice::SliceIndex;
 
+use unicode_xid::UnicodeXID;
+
 /// A featureful char-based scanner.
 #[derive(Copy, Clone)]
 pub struct Scanner<'s> {
@@ -114,6 +116,12 @@ impl<'s> Scanner<'s> {
         self.index = index;
     }
 
+    /// The full source string.
+    #[inline]
+    pub fn src(&self) -> &'s str {
+        &self.src
+    }
+
     /// Slice out part of the source string.
     #[inline]
     pub fn get<I>(&self, index: I) -> &'s str
@@ -150,6 +158,16 @@ impl<'s> Scanner<'s> {
         // optimized away in some cases.
         self.src.get(start .. self.index).unwrap_or_default()
     }
+
+    /// The column index of a given index in the source string.
+    #[inline]
+    pub fn column(&self, index: usize) -> usize {
+        self.src[.. index]
+            .chars()
+            .rev()
+            .take_while(|&c| !is_newline(c))
+            .count()
+    }
 }
 
 /// Whether this character denotes a newline.
@@ -163,3 +181,30 @@ pub fn is_newline(character: char) -> bool {
         '\u{0085}' | '\u{2028}' | '\u{2029}'
     )
 }
+
+/// Whether a string is a valid unicode identifier.
+///
+/// In addition to what is specified in the [Unicode Standard][uax31], we allow:
+/// - `_` as a starting character,
+/// - `_` and `-` as continuing characters.
+///
+/// [uax31]: http://www.unicode.org/reports/tr31/
+#[inline]
+pub fn is_ident(string: &str) -> bool {
+    let mut chars = string.chars();
+    chars
+        .next()
+        .map_or(false, |c| is_id_start(c) && chars.all(is_id_continue))
+}
+
+/// Whether a character can start an identifier.
+#[inline]
+pub fn is_id_start(c: char) -> bool {
+    c.is_xid_start() || c == '_'
+}
+
+/// Whether a character can continue an identifier.
+#[inline]
+pub fn is_id_continue(c: char) -> bool {
+    c.is_xid_continue() || c == '_' || c == '-'
+}
diff --git a/src/parse/tokens.rs b/src/parse/tokens.rs
index 5f969452..96dfd9d1 100644
--- a/src/parse/tokens.rs
+++ b/src/parse/tokens.rs
@@ -1,6 +1,13 @@
-use super::{is_newline, Scanner};
+use std::rc::Rc;
+
+use super::{
+    is_id_continue, is_id_start, is_newline, resolve_hex, resolve_raw, resolve_string,
+    Scanner,
+};
 use crate::geom::{AngularUnit, LengthUnit};
-use crate::syntax::*;
+use crate::syntax::ast::{MathNode, RawNode};
+use crate::syntax::{ErrorPos, NodeKind};
+use crate::util::EcoString;
 
 /// An iterator over the tokens of a string of source code.
 pub struct Tokens<'s> {
@@ -59,7 +66,7 @@ impl<'s> Tokens<'s> {
 }
 
 impl<'s> Iterator for Tokens<'s> {
-    type Item = Token<'s>;
+    type Item = NodeKind;
 
     /// Parse the next token in the source code.
     #[inline]
@@ -68,19 +75,21 @@ impl<'s> Iterator for Tokens<'s> {
         let c = self.s.eat()?;
         Some(match c {
             // Blocks and templates.
-            '[' => Token::LeftBracket,
-            ']' => Token::RightBracket,
-            '{' => Token::LeftBrace,
-            '}' => Token::RightBrace,
+            '[' => NodeKind::LeftBracket,
+            ']' => NodeKind::RightBracket,
+            '{' => NodeKind::LeftBrace,
+            '}' => NodeKind::RightBrace,
 
             // Whitespace.
-            ' ' if self.s.check_or(true, |c| !c.is_whitespace()) => Token::Space(0),
+            ' ' if self.s.check_or(true, |c| !c.is_whitespace()) => NodeKind::Space(0),
             c if c.is_whitespace() => self.whitespace(),
 
             // Comments with special case for URLs.
             '/' if self.s.eat_if('*') => self.block_comment(),
             '/' if !self.maybe_in_url() && self.s.eat_if('/') => self.line_comment(),
-            '*' if self.s.eat_if('/') => Token::Invalid(self.s.eaten_from(start)),
+            '*' if self.s.eat_if('/') => {
+                NodeKind::Unknown(self.s.eaten_from(start).into())
+            }
 
             // Other things.
             _ => match self.mode {
@@ -93,7 +102,7 @@ impl<'s> Iterator for Tokens<'s> {
 
 impl<'s> Tokens<'s> {
     #[inline]
-    fn markup(&mut self, start: usize, c: char) -> Token<'s> {
+    fn markup(&mut self, start: usize, c: char) -> NodeKind {
         match c {
             // Escape sequences.
             '\\' => self.backslash(),
@@ -102,13 +111,15 @@ impl<'s> Tokens<'s> {
             '#' => self.hash(),
 
             // Markup.
-            '~' => Token::Tilde,
-            '*' => Token::Star,
-            '_' => Token::Underscore,
+            '~' => NodeKind::NonBreakingSpace,
+            '*' => NodeKind::Strong,
+            '_' => NodeKind::Emph,
             '`' => self.raw(),
             '$' => self.math(),
-            '-' => self.hyph(start),
-            '=' if self.s.check_or(true, |c| c == '=' || c.is_whitespace()) => Token::Eq,
+            '-' => self.hyph(),
+            '=' if self.s.check_or(true, |c| c == '=' || c.is_whitespace()) => {
+                NodeKind::Eq
+            }
             c if c == '.' || c.is_ascii_digit() => self.numbering(start, c),
 
             // Plain text.
@@ -116,35 +127,35 @@ impl<'s> Tokens<'s> {
         }
     }
 
-    fn code(&mut self, start: usize, c: char) -> Token<'s> {
+    fn code(&mut self, start: usize, c: char) -> NodeKind {
         match c {
             // Parens.
-            '(' => Token::LeftParen,
-            ')' => Token::RightParen,
+            '(' => NodeKind::LeftParen,
+            ')' => NodeKind::RightParen,
 
             // Length two.
-            '=' if self.s.eat_if('=') => Token::EqEq,
-            '!' if self.s.eat_if('=') => Token::ExclEq,
-            '<' if self.s.eat_if('=') => Token::LtEq,
-            '>' if self.s.eat_if('=') => Token::GtEq,
-            '+' if self.s.eat_if('=') => Token::PlusEq,
-            '-' if self.s.eat_if('=') => Token::HyphEq,
-            '*' if self.s.eat_if('=') => Token::StarEq,
-            '/' if self.s.eat_if('=') => Token::SlashEq,
-            '.' if self.s.eat_if('.') => Token::Dots,
-            '=' if self.s.eat_if('>') => Token::Arrow,
+            '=' if self.s.eat_if('=') => NodeKind::EqEq,
+            '!' if self.s.eat_if('=') => NodeKind::ExclEq,
+            '<' if self.s.eat_if('=') => NodeKind::LtEq,
+            '>' if self.s.eat_if('=') => NodeKind::GtEq,
+            '+' if self.s.eat_if('=') => NodeKind::PlusEq,
+            '-' if self.s.eat_if('=') => NodeKind::HyphEq,
+            '*' if self.s.eat_if('=') => NodeKind::StarEq,
+            '/' if self.s.eat_if('=') => NodeKind::SlashEq,
+            '.' if self.s.eat_if('.') => NodeKind::Dots,
+            '=' if self.s.eat_if('>') => NodeKind::Arrow,
 
             // Length one.
-            ',' => Token::Comma,
-            ';' => Token::Semicolon,
-            ':' => Token::Colon,
-            '+' => Token::Plus,
-            '-' => Token::Hyph,
-            '*' => Token::Star,
-            '/' => Token::Slash,
-            '=' => Token::Eq,
-            '<' => Token::Lt,
-            '>' => Token::Gt,
+            ',' => NodeKind::Comma,
+            ';' => NodeKind::Semicolon,
+            ':' => NodeKind::Colon,
+            '+' => NodeKind::Plus,
+            '-' => NodeKind::Minus,
+            '*' => NodeKind::Star,
+            '/' => NodeKind::Slash,
+            '=' => NodeKind::Eq,
+            '<' => NodeKind::Lt,
+            '>' => NodeKind::Gt,
 
             // Identifiers.
             c if is_id_start(c) => self.ident(start),
@@ -159,12 +170,12 @@ impl<'s> Tokens<'s> {
             // Strings.
             '"' => self.string(),
 
-            _ => Token::Invalid(self.s.eaten_from(start)),
+            _ => NodeKind::Unknown(self.s.eaten_from(start).into()),
         }
     }
 
     #[inline]
-    fn text(&mut self, start: usize) -> Token<'s> {
+    fn text(&mut self, start: usize) -> NodeKind {
         macro_rules! table {
             ($($c:literal)|*) => {{
                 let mut t = [false; 128];
@@ -186,10 +197,10 @@ impl<'s> Tokens<'s> {
             TABLE.get(c as usize).copied().unwrap_or_else(|| c.is_whitespace())
         });
 
-        Token::Text(self.s.eaten_from(start))
+        NodeKind::Text(self.s.eaten_from(start).into())
     }
 
-    fn whitespace(&mut self) -> Token<'s> {
+    fn whitespace(&mut self) -> NodeKind {
         self.s.uneat();
 
         // Count the number of newlines.
@@ -208,73 +219,81 @@ impl<'s> Tokens<'s> {
             }
         }
 
-        Token::Space(newlines)
+        NodeKind::Space(newlines)
     }
 
-    fn backslash(&mut self) -> Token<'s> {
-        if let Some(c) = self.s.peek() {
-            match c {
+    fn backslash(&mut self) -> NodeKind {
+        match self.s.peek() {
+            Some(c) => match c {
                 // Backslash and comments.
                 '\\' | '/' |
                 // Parenthesis and hashtag.
                 '[' | ']' | '{' | '}' | '#' |
                 // Markup.
                 '*' | '_' | '=' | '~' | '`' | '$' => {
-                    let start = self.s.index();
                     self.s.eat_assert(c);
-                    Token::Text(&self.s.eaten_from(start))
+                    NodeKind::Text(c.into())
                 }
                 'u' if self.s.rest().starts_with("u{") => {
                     self.s.eat_assert('u');
                     self.s.eat_assert('{');
-                    Token::UnicodeEscape(UnicodeEscapeToken {
-                        // Allow more than `ascii_hexdigit` for better error recovery.
-                        sequence: self.s.eat_while(|c| c.is_ascii_alphanumeric()),
-                        terminated: self.s.eat_if('}'),
-                    })
+                    let sequence = self.s.eat_while(|c| c.is_ascii_alphanumeric());
+                    if self.s.eat_if('}') {
+                        if let Some(c) = resolve_hex(&sequence) {
+                            NodeKind::UnicodeEscape(c)
+                        } else {
+                            NodeKind::Error(
+                                ErrorPos::Full,
+                                "invalid unicode escape sequence".into(),
+                            )
+                        }
+                    } else {
+                        NodeKind::Error(
+                            ErrorPos::End,
+                            "expected closing brace".into(),
+                        )
+                    }
                 }
-                c if c.is_whitespace() => Token::Backslash,
-                _ => Token::Text("\\"),
-            }
-        } else {
-            Token::Backslash
+                c if c.is_whitespace() => NodeKind::Linebreak,
+                _ => NodeKind::Text('\\'.into()),
+            },
+            None => NodeKind::Linebreak,
         }
     }
 
     #[inline]
-    fn hash(&mut self) -> Token<'s> {
+    fn hash(&mut self) -> NodeKind {
         if self.s.check_or(false, is_id_start) {
             let read = self.s.eat_while(is_id_continue);
-            if let Some(keyword) = keyword(read) {
-                keyword
-            } else {
-                Token::Ident(read)
+            match keyword(read) {
+                Some(keyword) => keyword,
+                None => NodeKind::Ident(read.into()),
             }
         } else {
-            Token::Text("#")
+            NodeKind::Text("#".into())
         }
     }
 
-    fn hyph(&mut self, start: usize) -> Token<'s> {
+    fn hyph(&mut self) -> NodeKind {
         if self.s.eat_if('-') {
             if self.s.eat_if('-') {
-                Token::HyphHyphHyph
+                NodeKind::EmDash
             } else {
-                Token::HyphHyph
+                NodeKind::EnDash
             }
         } else if self.s.check_or(true, char::is_whitespace) {
-            Token::Hyph
+            NodeKind::Minus
         } else {
-            Token::Text(self.s.eaten_from(start))
+            NodeKind::Text("-".into())
         }
     }
 
-    fn numbering(&mut self, start: usize, c: char) -> Token<'s> {
+    fn numbering(&mut self, start: usize, c: char) -> NodeKind {
         let number = if c != '.' {
             self.s.eat_while(|c| c.is_ascii_digit());
             let read = self.s.eaten_from(start);
             if !self.s.eat_if('.') {
-                return Token::Text(read);
+                return NodeKind::Text(self.s.eaten_from(start).into());
             }
             read.parse().ok()
         } else {
@@ -282,13 +301,15 @@ impl<'s> Tokens<'s> {
         };
 
         if self.s.check_or(true, char::is_whitespace) {
-            Token::Numbering(number)
+            NodeKind::EnumNumbering(number)
         } else {
-            Token::Text(self.s.eaten_from(start))
+            NodeKind::Text(self.s.eaten_from(start).into())
         }
     }
 
-    fn raw(&mut self) -> Token<'s> {
+    fn raw(&mut self) -> NodeKind {
+        let column = self.s.column(self.s.index() - 1);
+
         let mut backticks = 1;
         while self.s.eat_if('`') {
             backticks += 1;
@@ -296,7 +317,11 @@ impl<'s> Tokens<'s> {
 
         // Special case for empty inline block.
         if backticks == 2 {
-            return Token::Raw(RawToken { text: "", backticks: 1, terminated: true });
+            return NodeKind::Raw(Rc::new(RawNode {
+                text: EcoString::new(),
+                lang: None,
+                block: false,
+            }));
         }
 
         let start = self.s.index();
@@ -310,17 +335,30 @@ impl<'s> Tokens<'s> {
             }
         }
 
-        let terminated = found == backticks;
-        let end = self.s.index() - if terminated { found } else { 0 };
+        if found == backticks {
+            let end = self.s.index() - found as usize;
+            NodeKind::Raw(Rc::new(resolve_raw(
+                column,
+                backticks,
+                self.s.get(start .. end).into(),
+            )))
+        } else {
+            let remaining = backticks - found;
+            let noun = if remaining == 1 { "backtick" } else { "backticks" };
 
-        Token::Raw(RawToken {
-            text: self.s.get(start .. end),
-            backticks,
-            terminated,
-        })
+            NodeKind::Error(
+                ErrorPos::End,
+                if found == 0 {
+                    format!("expected {} {}", remaining, noun)
+                } else {
+                    format!("expected {} more {}", remaining, noun)
+                }
+                .into(),
+            )
+        }
     }
 
-    fn math(&mut self) -> Token<'s> {
+    fn math(&mut self) -> NodeKind {
         let mut display = false;
         if self.s.eat_if('[') {
             display = true;
@@ -350,25 +388,36 @@ impl<'s> Tokens<'s> {
                 (true, true) => 2,
             };
 
-        Token::Math(MathToken {
-            formula: self.s.get(start .. end),
-            display,
-            terminated,
-        })
+        if terminated {
+            NodeKind::Math(Rc::new(MathNode {
+                formula: self.s.get(start .. end).into(),
+                display,
+            }))
+        } else {
+            NodeKind::Error(
+                ErrorPos::End,
+                if !display || (!escaped && dollar) {
+                    "expected closing dollar sign"
+                } else {
+                    "expected closing bracket and dollar sign"
+                }
+                .into(),
+            )
+        }
     }
 
-    fn ident(&mut self, start: usize) -> Token<'s> {
+    fn ident(&mut self, start: usize) -> NodeKind {
         self.s.eat_while(is_id_continue);
         match self.s.eaten_from(start) {
-            "none" => Token::None,
-            "auto" => Token::Auto,
-            "true" => Token::Bool(true),
-            "false" => Token::Bool(false),
-            id => keyword(id).unwrap_or(Token::Ident(id)),
+            "none" => NodeKind::None,
+            "auto" => NodeKind::Auto,
+            "true" => NodeKind::Bool(true),
+            "false" => NodeKind::Bool(false),
+            id => keyword(id).unwrap_or(NodeKind::Ident(id.into())),
         }
     }
 
-    fn number(&mut self, start: usize, c: char) -> Token<'s> {
+    fn number(&mut self, start: usize, c: char) -> NodeKind {
         // Read the first part (integer or fractional depending on `first`).
         self.s.eat_while(|c| c.is_ascii_digit());
 
@@ -396,55 +445,56 @@ impl<'s> Tokens<'s> {
 
         // Find out whether it is a simple number.
         if suffix.is_empty() {
-            if let Ok(int) = number.parse::<i64>() {
-                return Token::Int(int);
-            } else if let Ok(float) = number.parse::<f64>() {
-                return Token::Float(float);
+            if let Ok(i) = number.parse::<i64>() {
+                return NodeKind::Int(i);
             }
         }
 
-        // Otherwise parse into the fitting numeric type.
-        let build = match suffix {
-            "%" => Token::Percent,
-            "fr" => Token::Fraction,
-            "pt" => |x| Token::Length(x, LengthUnit::Pt),
-            "mm" => |x| Token::Length(x, LengthUnit::Mm),
-            "cm" => |x| Token::Length(x, LengthUnit::Cm),
-            "in" => |x| Token::Length(x, LengthUnit::In),
-            "rad" => |x| Token::Angle(x, AngularUnit::Rad),
-            "deg" => |x| Token::Angle(x, AngularUnit::Deg),
-            _ => return Token::Invalid(all),
-        };
-
-        if let Ok(float) = number.parse::<f64>() {
-            build(float)
+        if let Ok(f) = number.parse::<f64>() {
+            match suffix {
+                "" => NodeKind::Float(f),
+                "%" => NodeKind::Percentage(f),
+                "fr" => NodeKind::Fraction(f),
+                "pt" => NodeKind::Length(f, LengthUnit::Pt),
+                "mm" => NodeKind::Length(f, LengthUnit::Mm),
+                "cm" => NodeKind::Length(f, LengthUnit::Cm),
+                "in" => NodeKind::Length(f, LengthUnit::In),
+                "deg" => NodeKind::Angle(f, AngularUnit::Deg),
+                "rad" => NodeKind::Angle(f, AngularUnit::Rad),
+                _ => {
+                    return NodeKind::Unknown(all.into());
+                }
+            }
         } else {
-            Token::Invalid(all)
+            NodeKind::Unknown(all.into())
         }
     }
 
-    fn string(&mut self) -> Token<'s> {
+
+    fn string(&mut self) -> NodeKind {
         let mut escaped = false;
-        Token::Str(StrToken {
-            string: self.s.eat_until(|c| {
-                if c == '"' && !escaped {
-                    true
-                } else {
-                    escaped = c == '\\' && !escaped;
-                    false
-                }
-            }),
-            terminated: self.s.eat_if('"'),
-        })
-    }
+        let string = resolve_string(self.s.eat_until(|c| {
+            if c == '"' && !escaped {
+                true
+            } else {
+                escaped = c == '\\' && !escaped;
+                false
+            }
+        }));
 
-    fn line_comment(&mut self) -> Token<'s> {
-        Token::LineComment(self.s.eat_until(is_newline))
+        if self.s.eat_if('"') {
+            NodeKind::Str(string)
+        } else {
+            NodeKind::Error(ErrorPos::End, "expected quote".into())
+        }
     }
 
-    fn block_comment(&mut self) -> Token<'s> {
-        let start = self.s.index();
+    fn line_comment(&mut self) -> NodeKind {
+        self.s.eat_until(is_newline);
+        NodeKind::LineComment
+    }
 
+    fn block_comment(&mut self) -> NodeKind {
         let mut state = '_';
         let mut depth = 1;
 
@@ -466,10 +516,7 @@ impl<'s> Tokens<'s> {
             }
         }
 
-        let terminated = depth == 0;
-        let end = self.s.index() - if terminated { 2 } else { 0 };
-
-        Token::BlockComment(self.s.get(start .. end))
+        NodeKind::BlockComment
     }
 
     fn maybe_in_url(&self) -> bool {
@@ -477,24 +524,24 @@ impl<'s> Tokens<'s> {
     }
 }
 
-fn keyword(ident: &str) -> Option<Token<'static>> {
+fn keyword(ident: &str) -> Option<NodeKind> {
     Some(match ident {
-        "not" => Token::Not,
-        "and" => Token::And,
-        "or" => Token::Or,
-        "with" => Token::With,
-        "let" => Token::Let,
-        "if" => Token::If,
-        "else" => Token::Else,
-        "for" => Token::For,
-        "in" => Token::In,
-        "while" => Token::While,
-        "break" => Token::Break,
-        "continue" => Token::Continue,
-        "return" => Token::Return,
-        "import" => Token::Import,
-        "include" => Token::Include,
-        "from" => Token::From,
+        "not" => NodeKind::Not,
+        "and" => NodeKind::And,
+        "or" => NodeKind::Or,
+        "with" => NodeKind::With,
+        "let" => NodeKind::Let,
+        "if" => NodeKind::If,
+        "else" => NodeKind::Else,
+        "for" => NodeKind::For,
+        "in" => NodeKind::In,
+        "while" => NodeKind::While,
+        "break" => NodeKind::Break,
+        "continue" => NodeKind::Continue,
+        "return" => NodeKind::Return,
+        "import" => NodeKind::Import,
+        "include" => NodeKind::Include,
+        "from" => NodeKind::From,
         _ => return None,
     })
 }
@@ -506,24 +553,45 @@ mod tests {
 
     use super::*;
 
+    use ErrorPos::*;
+    use NodeKind::*;
     use Option::None;
-    use Token::{Ident, *};
     use TokenMode::{Code, Markup};
 
-    const fn UnicodeEscape(sequence: &str, terminated: bool) -> Token {
-        Token::UnicodeEscape(UnicodeEscapeToken { sequence, terminated })
+    fn UnicodeEscape(c: char) -> NodeKind {
+        NodeKind::UnicodeEscape(c)
     }
 
-    const fn Raw(text: &str, backticks: usize, terminated: bool) -> Token {
-        Token::Raw(RawToken { text, backticks, terminated })
+    fn Error(pos: ErrorPos, message: &str) -> NodeKind {
+        NodeKind::Error(pos, message.into())
     }
 
-    const fn Math(formula: &str, display: bool, terminated: bool) -> Token {
-        Token::Math(MathToken { formula, display, terminated })
+    fn Raw(text: &str, lang: Option<&str>, block: bool) -> NodeKind {
+        NodeKind::Raw(Rc::new(RawNode {
+            text: text.into(),
+            lang: lang.map(Into::into),
+            block,
+        }))
     }
 
-    const fn Str(string: &str, terminated: bool) -> Token {
-        Token::Str(StrToken { string, terminated })
+    fn Math(formula: &str, display: bool) -> NodeKind {
+        NodeKind::Math(Rc::new(MathNode { formula: formula.into(), display }))
+    }
+
+    fn Str(string: &str) -> NodeKind {
+        NodeKind::Str(string.into())
+    }
+
+    fn Text(string: &str) -> NodeKind {
+        NodeKind::Text(string.into())
+    }
+
+    fn Ident(ident: &str) -> NodeKind {
+        NodeKind::Ident(ident.into())
+    }
+
+    fn Invalid(invalid: &str) -> NodeKind {
+        NodeKind::Unknown(invalid.into())
     }
 
     /// Building blocks for suffix testing.
@@ -541,40 +609,6 @@ mod tests {
     /// - '/': symbols
     const BLOCKS: &str = " a1/";
 
-    /// Suffixes described by four-tuples of:
-    ///
-    /// - block the suffix is part of
-    /// - mode in which the suffix is applicable
-    /// - the suffix string
-    /// - the resulting suffix token
-    const SUFFIXES: &[(char, Option<TokenMode>, &str, Token)] = &[
-        // Whitespace suffixes.
-        (' ', None, " ", Space(0)),
-        (' ', None, "\n", Space(1)),
-        (' ', None, "\r", Space(1)),
-        (' ', None, "\r\n", Space(1)),
-        // Letter suffixes.
-        ('a', Some(Markup), "hello", Text("hello")),
-        ('a', Some(Markup), "💚", Text("💚")),
-        ('a', Some(Code), "val", Ident("val")),
-        ('a', Some(Code), "α", Ident("α")),
-        ('a', Some(Code), "_", Ident("_")),
-        // Number suffixes.
-        ('1', Some(Code), "2", Int(2)),
-        ('1', Some(Code), ".2", Float(0.2)),
-        // Symbol suffixes.
-        ('/', None, "[", LeftBracket),
-        ('/', None, "//", LineComment("")),
-        ('/', None, "/**/", BlockComment("")),
-        ('/', Some(Markup), "*", Star),
-        ('/', Some(Markup), "$ $", Math(" ", false, true)),
-        ('/', Some(Markup), r"\\", Text(r"\")),
-        ('/', Some(Markup), "#let", Let),
-        ('/', Some(Code), "(", LeftParen),
-        ('/', Some(Code), ":", Colon),
-        ('/', Some(Code), "+=", PlusEq),
-    ];
-
     macro_rules! t {
         (Both $($tts:tt)*) => {
             t!(Markup $($tts)*);
@@ -584,8 +618,42 @@ mod tests {
             // Test without suffix.
             t!(@$mode: $src => $($token),*);
 
+            // Suffixes described by four-tuples of:
+            //
+            // - block the suffix is part of
+            // - mode in which the suffix is applicable
+            // - the suffix string
+            // - the resulting suffix NodeKind
+            let suffixes: &[(char, Option<TokenMode>, &str, NodeKind)] = &[
+                // Whitespace suffixes.
+                (' ', None, " ", Space(0)),
+                (' ', None, "\n", Space(1)),
+                (' ', None, "\r", Space(1)),
+                (' ', None, "\r\n", Space(1)),
+                // Letter suffixes.
+                ('a', Some(Markup), "hello", Text("hello")),
+                ('a', Some(Markup), "💚", Text("💚")),
+                ('a', Some(Code), "val", Ident("val")),
+                ('a', Some(Code), "α", Ident("α")),
+                ('a', Some(Code), "_", Ident("_")),
+                // Number suffixes.
+                ('1', Some(Code), "2", Int(2)),
+                ('1', Some(Code), ".2", Float(0.2)),
+                // Symbol suffixes.
+                ('/', None, "[", LeftBracket),
+                ('/', None, "//", LineComment),
+                ('/', None, "/**/", BlockComment),
+                ('/', Some(Markup), "*", Strong),
+                ('/', Some(Markup), "$ $", Math(" ", false)),
+                ('/', Some(Markup), r"\\", Text("\\")),
+                ('/', Some(Markup), "#let", Let),
+                ('/', Some(Code), "(", LeftParen),
+                ('/', Some(Code), ":", Colon),
+                ('/', Some(Code), "+=", PlusEq),
+            ];
+
             // Test with each applicable suffix.
-            for &(block, mode, suffix, token) in SUFFIXES {
+            for &(block, mode, suffix, ref token) in suffixes {
                 let src = $src;
                 #[allow(unused_variables)]
                 let blocks = BLOCKS;
@@ -599,7 +667,7 @@ mod tests {
         (@$mode:ident: $src:expr => $($token:expr),*) => {{
             let src = $src;
             let found = Tokens::new(&src, $mode).collect::<Vec<_>>();
-            let expected = vec![$($token),*];
+            let expected = vec![$($token.clone()),*];
             check(&src, found, expected);
         }};
     }
@@ -671,7 +739,7 @@ mod tests {
 
         // Test text ends.
         t!(Markup[""]: "hello " => Text("hello"), Space(0));
-        t!(Markup[""]: "hello~" => Text("hello"), Tilde);
+        t!(Markup[""]: "hello~" => Text("hello"), NonBreakingSpace);
     }
 
     #[test]
@@ -698,31 +766,31 @@ mod tests {
         t!(Markup[" /"]: r#"\""# => Text(r"\"), Text("\""));
 
         // Test basic unicode escapes.
-        t!(Markup: r"\u{}"     => UnicodeEscape("", true));
-        t!(Markup: r"\u{2603}" => UnicodeEscape("2603", true));
-        t!(Markup: r"\u{P}"    => UnicodeEscape("P", true));
+        t!(Markup: r"\u{}"     => Error(Full, "invalid unicode escape sequence"));
+        t!(Markup: r"\u{2603}" => UnicodeEscape('☃'));
+        t!(Markup: r"\u{P}"    => Error(Full, "invalid unicode escape sequence"));
 
         // Test unclosed unicode escapes.
-        t!(Markup[" /"]: r"\u{"     => UnicodeEscape("", false));
-        t!(Markup[" /"]: r"\u{1"    => UnicodeEscape("1", false));
-        t!(Markup[" /"]: r"\u{26A4" => UnicodeEscape("26A4", false));
-        t!(Markup[" /"]: r"\u{1Q3P" => UnicodeEscape("1Q3P", false));
-        t!(Markup: r"\u{1🏕}"       => UnicodeEscape("1", false), Text("🏕"), RightBrace);
+        t!(Markup[" /"]: r"\u{"     => Error(End, "expected closing brace"));
+        t!(Markup[" /"]: r"\u{1"    => Error(End, "expected closing brace"));
+        t!(Markup[" /"]: r"\u{26A4" => Error(End, "expected closing brace"));
+        t!(Markup[" /"]: r"\u{1Q3P" => Error(End, "expected closing brace"));
+        t!(Markup: r"\u{1🏕}"       => Error(End, "expected closing brace"), Text("🏕"), RightBrace);
     }
 
     #[test]
     fn test_tokenize_markup_symbols() {
         // Test markup tokens.
-        t!(Markup[" a1"]: "*"   => Star);
-        t!(Markup: "_"          => Underscore);
+        t!(Markup[" a1"]: "*"   => Strong);
+        t!(Markup: "_"          => Emph);
         t!(Markup[""]: "==="    => Eq, Eq, Eq);
         t!(Markup["a1/"]: "= "  => Eq, Space(0));
-        t!(Markup: "~"          => Tilde);
-        t!(Markup[" "]: r"\"    => Backslash);
-        t!(Markup["a "]: r"a--" => Text("a"), HyphHyph);
-        t!(Markup["a1/"]: "- "  => Hyph, Space(0));
-        t!(Markup[" "]: "."     => Numbering(None));
-        t!(Markup[" "]: "1."    => Numbering(Some(1)));
+        t!(Markup: "~"          => NonBreakingSpace);
+        t!(Markup[" "]: r"\"    => Linebreak);
+        t!(Markup["a "]: r"a--" => Text("a"), EnDash);
+        t!(Markup["a1/"]: "- "  => Minus, Space(0));
+        t!(Markup[" "]: "."     => EnumNumbering(None));
+        t!(Markup[" "]: "1."    => EnumNumbering(Some(1)));
         t!(Markup[" "]: "1.a"   => Text("1."), Text("a"));
         t!(Markup[" /"]: "a1."  => Text("a1."));
     }
@@ -734,7 +802,7 @@ mod tests {
         t!(Code: ";"        => Semicolon);
         t!(Code: ":"        => Colon);
         t!(Code: "+"        => Plus);
-        t!(Code: "-"        => Hyph);
+        t!(Code: "-"        => Minus);
         t!(Code[" a1"]: "*" => Star);
         t!(Code[" a1"]: "/" => Slash);
         t!(Code: "="        => Eq);
@@ -756,10 +824,10 @@ mod tests {
         t!(Code[" a/"]: "..." => Dots, Invalid("."));
 
         // Test hyphen as symbol vs part of identifier.
-        t!(Code[" /"]: "-1"   => Hyph, Int(1));
-        t!(Code[" /"]: "-a"   => Hyph, Ident("a"));
-        t!(Code[" /"]: "--1"  => Hyph, Hyph, Int(1));
-        t!(Code[" /"]: "--_a" => Hyph, Hyph, Ident("_a"));
+        t!(Code[" /"]: "-1"   => Minus, Int(1));
+        t!(Code[" /"]: "-a"   => Minus, Ident("a"));
+        t!(Code[" /"]: "--1"  => Minus, Minus, Int(1));
+        t!(Code[" /"]: "--_a" => Minus, Minus, Ident("_a"));
         t!(Code[" /"]: "a-b"  => Ident("a-b"));
     }
 
@@ -776,13 +844,13 @@ mod tests {
             ("import", Import),
         ];
 
-        for &(s, t) in &list {
+        for (s, t) in list.clone() {
             t!(Markup[" "]: format!("#{}", s) => t);
             t!(Markup[" "]: format!("#{0}#{0}", s) => t, t);
-            t!(Markup[" /"]: format!("# {}", s) => Token::Text("#"), Space(0), Text(s));
+            t!(Markup[" /"]: format!("# {}", s) => Text("#"), Space(0), Text(s));
         }
 
-        for &(s, t) in &list {
+        for (s, t) in list {
             t!(Code[" "]: s => t);
             t!(Markup[" /"]: s => Text(s));
         }
@@ -796,45 +864,43 @@ mod tests {
 
     #[test]
     fn test_tokenize_raw_blocks() {
-        let empty = Raw("", 1, true);
-
         // Test basic raw block.
-        t!(Markup: "``"     => empty);
-        t!(Markup: "`raw`"  => Raw("raw", 1, true));
-        t!(Markup[""]: "`]" => Raw("]", 1, false));
+        t!(Markup: "``"     => Raw("", None, false));
+        t!(Markup: "`raw`"  => Raw("raw", None, false));
+        t!(Markup[""]: "`]" => Error(End, "expected 1 backtick"));
 
         // Test special symbols in raw block.
-        t!(Markup: "`[brackets]`" => Raw("[brackets]", 1, true));
-        t!(Markup[""]: r"`\`` "   => Raw(r"\", 1, true), Raw(" ", 1, false));
+        t!(Markup: "`[brackets]`" => Raw("[brackets]", None, false));
+        t!(Markup[""]: r"`\`` "   => Raw(r"\", None, false), Error(End, "expected 1 backtick"));
 
         // Test separated closing backticks.
-        t!(Markup: "```not `y`e`t```" => Raw("not `y`e`t", 3, true));
+        t!(Markup: "```not `y`e`t```" => Raw("`y`e`t", Some("not"), false));
 
         // Test more backticks.
-        t!(Markup: "``nope``"             => empty, Text("nope"), empty);
-        t!(Markup: "````🚀````"           => Raw("🚀", 4, true));
-        t!(Markup[""]: "`````👩‍🚀````noend" => Raw("👩‍🚀````noend", 5, false));
-        t!(Markup[""]: "````raw``````"    => Raw("raw", 4, true), empty);
+        t!(Markup: "``nope``"             => Raw("", None, false), Text("nope"), Raw("", None, false));
+        t!(Markup: "````🚀````"           => Raw("", None, false));
+        t!(Markup[""]: "`````👩‍🚀````noend" => Error(End, "expected 5 backticks"));
+        t!(Markup[""]: "````raw``````"    => Raw("", Some("raw"), false), Raw("", None, false));
     }
 
     #[test]
     fn test_tokenize_math_formulas() {
         // Test basic formula.
-        t!(Markup: "$$"        => Math("", false, true));
-        t!(Markup: "$x$"       => Math("x", false, true));
-        t!(Markup: r"$\\$"     => Math(r"\\", false, true));
-        t!(Markup: "$[x + y]$" => Math("x + y", true, true));
-        t!(Markup: r"$[\\]$"   => Math(r"\\", true, true));
+        t!(Markup: "$$"        => Math("", false));
+        t!(Markup: "$x$"       => Math("x", false));
+        t!(Markup: r"$\\$"     => Math(r"\\", false));
+        t!(Markup: "$[x + y]$" => Math("x + y", true));
+        t!(Markup: r"$[\\]$"   => Math(r"\\", true));
 
         // Test unterminated.
-        t!(Markup[""]: "$x"      => Math("x", false, false));
-        t!(Markup[""]: "$[x"     => Math("x", true, false));
-        t!(Markup[""]: "$[x]\n$" => Math("x]\n$", true, false));
+        t!(Markup[""]: "$x"      => Error(End, "expected closing dollar sign"));
+        t!(Markup[""]: "$[x"     => Error(End, "expected closing bracket and dollar sign"));
+        t!(Markup[""]: "$[x]\n$" => Error(End, "expected closing bracket and dollar sign"));
 
         // Test escape sequences.
-        t!(Markup: r"$\$x$"       => Math(r"\$x", false, true));
-        t!(Markup: r"$[\\\]$]$"   => Math(r"\\\]$", true, true));
-        t!(Markup[""]: r"$[ ]\\$" => Math(r" ]\\$", true, false));
+        t!(Markup: r"$\$x$"       => Math(r"\$x", false));
+        t!(Markup: r"$[\\\]$]$"   => Math(r"\\\]$", true));
+        t!(Markup[""]: r"$[ ]\\$" => Error(End, "expected closing bracket and dollar sign"));
     }
 
     #[test]
@@ -896,8 +962,8 @@ mod tests {
         let nums = ints.iter().map(|&(k, v)| (k, v as f64)).chain(floats);
 
         let suffixes = [
-            ("%", Percent as fn(f64) -> Token<'static>),
-            ("fr", Fraction as fn(f64) -> Token<'static>),
+            ("%", Percentage as fn(f64) -> NodeKind),
+            ("fr", Fraction as fn(f64) -> NodeKind),
             ("mm", |x| Length(x, LengthUnit::Mm)),
             ("pt", |x| Length(x, LengthUnit::Pt)),
             ("cm", |x| Length(x, LengthUnit::Cm)),
@@ -922,62 +988,62 @@ mod tests {
     #[test]
     fn test_tokenize_strings() {
         // Test basic strings.
-        t!(Code: "\"hi\""        => Str("hi", true));
-        t!(Code: "\"hi\nthere\"" => Str("hi\nthere", true));
-        t!(Code: "\"🌎\""        => Str("🌎", true));
+        t!(Code: "\"hi\""        => Str("hi"));
+        t!(Code: "\"hi\nthere\"" => Str("hi\nthere"));
+        t!(Code: "\"🌎\""        => Str("🌎"));
 
         // Test unterminated.
-        t!(Code[""]: "\"hi"      => Str("hi", false));
+        t!(Code[""]: "\"hi" => Error(End, "expected quote"));
 
         // Test escaped quote.
-        t!(Code: r#""a\"bc""# => Str(r#"a\"bc"#, true));
-        t!(Code[""]: r#""\""# => Str(r#"\""#, false));
+        t!(Code: r#""a\"bc""# => Str("a\"bc"));
+        t!(Code[""]: r#""\""# => Error(End, "expected quote"));
     }
 
     #[test]
     fn test_tokenize_line_comments() {
         // Test line comment with no trailing newline.
-        t!(Both[""]: "//" => LineComment(""));
+        t!(Both[""]: "//" => LineComment);
 
         // Test line comment ends at newline.
-        t!(Both["a1/"]: "//bc\n"   => LineComment("bc"), Space(1));
-        t!(Both["a1/"]: "// bc \n" => LineComment(" bc "), Space(1));
-        t!(Both["a1/"]: "//bc\r\n" => LineComment("bc"), Space(1));
+        t!(Both["a1/"]: "//bc\n"   => LineComment, Space(1));
+        t!(Both["a1/"]: "// bc \n" => LineComment, Space(1));
+        t!(Both["a1/"]: "//bc\r\n" => LineComment, Space(1));
 
         // Test nested line comments.
-        t!(Both["a1/"]: "//a//b\n" => LineComment("a//b"), Space(1));
+        t!(Both["a1/"]: "//a//b\n" => LineComment, Space(1));
     }
 
     #[test]
     fn test_tokenize_block_comments() {
         // Test basic block comments.
-        t!(Both[""]: "/*" => BlockComment(""));
-        t!(Both: "/**/"   => BlockComment(""));
-        t!(Both: "/*🏞*/" => BlockComment("🏞"));
-        t!(Both: "/*\n*/" => BlockComment("\n"));
+        t!(Both[""]: "/*" => BlockComment);
+        t!(Both: "/**/"   => BlockComment);
+        t!(Both: "/*🏞*/" => BlockComment);
+        t!(Both: "/*\n*/" => BlockComment);
 
         // Test depth 1 and 2 nested block comments.
-        t!(Both: "/* /* */ */"  => BlockComment(" /* */ "));
-        t!(Both: "/*/*/**/*/*/" => BlockComment("/*/**/*/"));
+        t!(Both: "/* /* */ */"  => BlockComment);
+        t!(Both: "/*/*/**/*/*/" => BlockComment);
 
         // Test two nested, one unclosed block comments.
-        t!(Both[""]: "/*/*/**/*/" => BlockComment("/*/**/*/"));
+        t!(Both[""]: "/*/*/**/*/" => BlockComment);
 
         // Test all combinations of up to two following slashes and stars.
-        t!(Both[""]: "/*"   => BlockComment(""));
-        t!(Both[""]: "/*/"  => BlockComment("/"));
-        t!(Both[""]: "/**"  => BlockComment("*"));
-        t!(Both[""]: "/*//" => BlockComment("//"));
-        t!(Both[""]: "/*/*" => BlockComment("/*"));
-        t!(Both[""]: "/**/" => BlockComment(""));
-        t!(Both[""]: "/***" => BlockComment("**"));
+        t!(Both[""]: "/*"   => BlockComment);
+        t!(Both[""]: "/*/"  => BlockComment);
+        t!(Both[""]: "/**"  => BlockComment);
+        t!(Both[""]: "/*//" => BlockComment);
+        t!(Both[""]: "/*/*" => BlockComment);
+        t!(Both[""]: "/**/" => BlockComment);
+        t!(Both[""]: "/***" => BlockComment);
     }
 
     #[test]
     fn test_tokenize_invalid() {
         // Test invalidly closed block comments.
-        t!(Both: "*/"     => Token::Invalid("*/"));
-        t!(Both: "/**/*/" => BlockComment(""), Token::Invalid("*/"));
+        t!(Both: "*/"     => Invalid("*/"));
+        t!(Both: "/**/*/" => BlockComment, Invalid("*/"));
 
         // Test invalid expressions.
         t!(Code: r"\"        => Invalid(r"\"));
@@ -990,6 +1056,6 @@ mod tests {
         // Test invalid number suffixes.
         t!(Code[" /"]: "1foo" => Invalid("1foo"));
         t!(Code: "1p%"        => Invalid("1p"), Invalid("%"));
-        t!(Code: "1%%"        => Percent(1.0), Invalid("%"));
+        t!(Code: "1%%"        => Percentage(1.0), Invalid("%"));
     }
 }
diff --git a/src/source.rs b/src/source.rs
index c9164f90..85f48491 100644
--- a/src/source.rs
+++ b/src/source.rs
@@ -8,8 +8,11 @@ use std::rc::Rc;
 
 use serde::{Deserialize, Serialize};
 
+use crate::diag::TypResult;
 use crate::loading::{FileHash, Loader};
-use crate::parse::{is_newline, Scanner};
+use crate::parse::{is_newline, parse, Scanner};
+use crate::syntax::ast::Markup;
+use crate::syntax::{GreenNode, RedNode};
 use crate::util::PathExt;
 
 #[cfg(feature = "codespan-reporting")]
@@ -124,6 +127,7 @@ pub struct SourceFile {
     path: PathBuf,
     src: String,
     line_starts: Vec<usize>,
+    root: Rc<GreenNode>,
 }
 
 impl SourceFile {
@@ -134,11 +138,23 @@ impl SourceFile {
         Self {
             id,
             path: path.normalize(),
+            root: parse(&src),
             src,
             line_starts,
         }
     }
 
+    /// The file's abstract syntax tree.
+    pub fn ast(&self) -> TypResult<Markup> {
+        let red = RedNode::from_root(self.root.clone(), self.id);
+        let errors = red.errors();
+        if errors.is_empty() {
+            Ok(red.cast().unwrap())
+        } else {
+            Err(Box::new(errors))
+        }
+    }
+
     /// Create a source file without a real id and path, usually for testing.
     pub fn detached(src: impl Into<String>) -> Self {
         Self::new(SourceId(0), Path::new(""), src.into())
diff --git a/src/syntax/ast.rs b/src/syntax/ast.rs
new file mode 100644
index 00000000..288c749a
--- /dev/null
+++ b/src/syntax/ast.rs
@@ -0,0 +1,988 @@
+//! A typed layer over the red-green tree.
+
+use std::ops::Deref;
+
+use super::{Green, GreenData, NodeKind, RedNode, RedRef, Span};
+use crate::geom::{AngularUnit, LengthUnit};
+use crate::util::EcoString;
+
+/// A typed AST node.
+pub trait TypedNode: Sized {
+    /// Convert from a red node to a typed node.
+    fn from_red(value: RedRef) -> Option<Self>;
+
+    /// A reference to the underlying red node.
+    fn as_red(&self) -> RedRef<'_>;
+
+    /// The source code location.
+    fn span(&self) -> Span {
+        self.as_red().span()
+    }
+}
+
+macro_rules! node {
+    ($(#[$attr:meta])* $name:ident) => {
+        node!{$(#[$attr])* $name: $name}
+    };
+    ($(#[$attr:meta])* $name:ident: $variant:ident) => {
+        node!{$(#[$attr])* $name: NodeKind::$variant}
+    };
+    ($(#[$attr:meta])* $name:ident: $($variant:pat)|*) => {
+        #[derive(Debug, Clone, PartialEq)]
+        #[repr(transparent)]
+        $(#[$attr])*
+        pub struct $name(RedNode);
+
+        impl TypedNode for $name {
+            fn from_red(node: RedRef) -> Option<Self> {
+                if matches!(node.kind(), $($variant)|*) {
+                    Some(Self(node.own()))
+                } else {
+                    None
+                }
+            }
+
+            fn as_red(&self) -> RedRef<'_> {
+                self.0.as_ref()
+            }
+        }
+    };
+}
+
+node! {
+    /// The syntactical root capable of representing a full parsed document.
+    Markup
+}
+
+impl Markup {
+    /// The markup nodes.
+    pub fn nodes(&self) -> impl Iterator<Item = MarkupNode> + '_ {
+        self.0.children().filter_map(|node| match node.kind() {
+            NodeKind::Space(_) => Some(MarkupNode::Space),
+            NodeKind::Linebreak => Some(MarkupNode::Linebreak),
+            NodeKind::Parbreak => Some(MarkupNode::Parbreak),
+            NodeKind::Strong => Some(MarkupNode::Strong),
+            NodeKind::Emph => Some(MarkupNode::Emph),
+            NodeKind::Text(s) => Some(MarkupNode::Text(s.clone())),
+            NodeKind::UnicodeEscape(c) => Some(MarkupNode::Text((*c).into())),
+            NodeKind::EnDash => Some(MarkupNode::Text("\u{2013}".into())),
+            NodeKind::EmDash => Some(MarkupNode::Text("\u{2014}".into())),
+            NodeKind::NonBreakingSpace => Some(MarkupNode::Text("\u{00A0}".into())),
+            NodeKind::Math(math) => Some(MarkupNode::Math(math.as_ref().clone())),
+            NodeKind::Raw(raw) => Some(MarkupNode::Raw(raw.as_ref().clone())),
+            NodeKind::Heading => node.cast().map(MarkupNode::Heading),
+            NodeKind::List => node.cast().map(MarkupNode::List),
+            NodeKind::Enum => node.cast().map(MarkupNode::Enum),
+            _ => node.cast().map(MarkupNode::Expr),
+        })
+    }
+}
+
+/// A single piece of markup.
+#[derive(Debug, Clone, PartialEq)]
+pub enum MarkupNode {
+    /// Whitespace containing less than two newlines.
+    Space,
+    /// A forced line break: `\`.
+    Linebreak,
+    /// A paragraph break: Two or more newlines.
+    Parbreak,
+    /// Strong text was enabled / disabled: `*`.
+    Strong,
+    /// Emphasized text was enabled / disabled: `_`.
+    Emph,
+    /// Plain text.
+    Text(EcoString),
+    /// A raw block with optional syntax highlighting: `` `...` ``.
+    Raw(RawNode),
+    /// A math formula: `$a^2 = b^2 + c^2$`.
+    Math(MathNode),
+    /// A section heading: `= Introduction`.
+    Heading(HeadingNode),
+    /// An item in an unordered list: `- ...`.
+    List(ListNode),
+    /// An item in an enumeration (ordered list): `1. ...`.
+    Enum(EnumNode),
+    /// An expression.
+    Expr(Expr),
+}
+
+/// A raw block with optional syntax highlighting: `` `...` ``.
+#[derive(Debug, Clone, PartialEq)]
+pub struct RawNode {
+    /// An optional identifier specifying the language to syntax-highlight in.
+    pub lang: Option<EcoString>,
+    /// The raw text, determined as the raw string between the backticks trimmed
+    /// according to the above rules.
+    pub text: EcoString,
+    /// Whether the element is block-level, that is, it has 3+ backticks
+    /// and contains at least one newline.
+    pub block: bool,
+}
+
+/// A math formula: `$a^2 + b^2 = c^2$`.
+#[derive(Debug, Clone, PartialEq)]
+pub struct MathNode {
+    /// The formula between the dollars / brackets.
+    pub formula: EcoString,
+    /// Whether the formula is display-level, that is, it is surrounded by
+    /// `$[..]$`.
+    pub display: bool,
+}
+
+node! {
+    /// A section heading: `= Introduction`.
+    HeadingNode: Heading
+}
+
+impl HeadingNode {
+    /// The contents of the heading.
+    pub fn body(&self) -> Markup {
+        self.0.cast_first_child().expect("heading is missing markup body")
+    }
+
+    /// The section depth (numer of equals signs).
+    pub fn level(&self) -> usize {
+        self.0.children().filter(|n| n.kind() == &NodeKind::Eq).count()
+    }
+}
+
+node! {
+    /// An item in an unordered list: `- ...`.
+    ListNode: List
+}
+
+impl ListNode {
+    /// The contents of the list item.
+    pub fn body(&self) -> Markup {
+        self.0.cast_first_child().expect("list node is missing body")
+    }
+}
+
+node! {
+    /// An item in an enumeration (ordered list): `1. ...`.
+    EnumNode: Enum
+}
+
+impl EnumNode {
+    /// The contents of the list item.
+    pub fn body(&self) -> Markup {
+        self.0.cast_first_child().expect("enum node is missing body")
+    }
+
+    /// The number, if any.
+    pub fn number(&self) -> Option<usize> {
+        self.0
+            .children()
+            .find_map(|node| match node.kind() {
+                NodeKind::EnumNumbering(num) => Some(num.clone()),
+                _ => None,
+            })
+            .expect("enum node is missing number")
+    }
+}
+
+/// An expression.
+#[derive(Debug, Clone, PartialEq)]
+pub enum Expr {
+    /// A literal: `1`, `true`, ...
+    Lit(Lit),
+    /// An identifier: `left`.
+    Ident(Ident),
+    /// An array expression: `(1, "hi", 12cm)`.
+    Array(ArrayExpr),
+    /// A dictionary expression: `(thickness: 3pt, pattern: dashed)`.
+    Dict(DictExpr),
+    /// A template expression: `[*Hi* there!]`.
+    Template(TemplateExpr),
+    /// A grouped expression: `(1 + 2)`.
+    Group(GroupExpr),
+    /// A block expression: `{ let x = 1; x + 2 }`.
+    Block(BlockExpr),
+    /// A unary operation: `-x`.
+    Unary(UnaryExpr),
+    /// A binary operation: `a + b`.
+    Binary(BinaryExpr),
+    /// An invocation of a function: `f(x, y)`.
+    Call(CallExpr),
+    /// A closure expression: `(x, y) => z`.
+    Closure(ClosureExpr),
+    /// A with expression: `f with (x, y: 1)`.
+    With(WithExpr),
+    /// A let expression: `let x = 1`.
+    Let(LetExpr),
+    /// An if-else expression: `if x { y } else { z }`.
+    If(IfExpr),
+    /// A while loop expression: `while x { y }`.
+    While(WhileExpr),
+    /// A for loop expression: `for x in y { z }`.
+    For(ForExpr),
+    /// An import expression: `import a, b, c from "utils.typ"`.
+    Import(ImportExpr),
+    /// An include expression: `include "chapter1.typ"`.
+    Include(IncludeExpr),
+}
+
+impl TypedNode for Expr {
+    fn from_red(node: RedRef) -> Option<Self> {
+        match node.kind() {
+            NodeKind::Ident(_) => node.cast().map(Self::Ident),
+            NodeKind::Array => node.cast().map(Self::Array),
+            NodeKind::Dict => node.cast().map(Self::Dict),
+            NodeKind::Template => node.cast().map(Self::Template),
+            NodeKind::Group => node.cast().map(Self::Group),
+            NodeKind::Block => node.cast().map(Self::Block),
+            NodeKind::Unary => node.cast().map(Self::Unary),
+            NodeKind::Binary => node.cast().map(Self::Binary),
+            NodeKind::Call => node.cast().map(Self::Call),
+            NodeKind::Closure => node.cast().map(Self::Closure),
+            NodeKind::WithExpr => node.cast().map(Self::With),
+            NodeKind::LetExpr => node.cast().map(Self::Let),
+            NodeKind::IfExpr => node.cast().map(Self::If),
+            NodeKind::WhileExpr => node.cast().map(Self::While),
+            NodeKind::ForExpr => node.cast().map(Self::For),
+            NodeKind::ImportExpr => node.cast().map(Self::Import),
+            NodeKind::IncludeExpr => node.cast().map(Self::Include),
+            _ => node.cast().map(Self::Lit),
+        }
+    }
+
+    fn as_red(&self) -> RedRef<'_> {
+        match self {
+            Self::Lit(v) => v.as_red(),
+            Self::Ident(v) => v.as_red(),
+            Self::Array(v) => v.as_red(),
+            Self::Dict(v) => v.as_red(),
+            Self::Template(v) => v.as_red(),
+            Self::Group(v) => v.as_red(),
+            Self::Block(v) => v.as_red(),
+            Self::Unary(v) => v.as_red(),
+            Self::Binary(v) => v.as_red(),
+            Self::Call(v) => v.as_red(),
+            Self::Closure(v) => v.as_red(),
+            Self::With(v) => v.as_red(),
+            Self::Let(v) => v.as_red(),
+            Self::If(v) => v.as_red(),
+            Self::While(v) => v.as_red(),
+            Self::For(v) => v.as_red(),
+            Self::Import(v) => v.as_red(),
+            Self::Include(v) => v.as_red(),
+        }
+    }
+}
+
+impl Expr {
+    /// Whether the expression can be shortened in markup with a hashtag.
+    pub fn has_short_form(&self) -> bool {
+        matches!(self,
+            Self::Ident(_)
+            | Self::Call(_)
+            | Self::Let(_)
+            | Self::If(_)
+            | Self::While(_)
+            | Self::For(_)
+            | Self::Import(_)
+            | Self::Include(_)
+        )
+    }
+}
+
+node! {
+    /// A literal: `1`, `true`, ...
+    Lit: NodeKind::None
+       | NodeKind::Auto
+       | NodeKind::Bool(_)
+       | NodeKind::Int(_)
+       | NodeKind::Float(_)
+       | NodeKind::Length(_, _)
+       | NodeKind::Angle(_, _)
+       | NodeKind::Percentage(_)
+       | NodeKind::Fraction(_)
+       | NodeKind::Str(_)
+}
+
+impl Lit {
+    /// The kind of literal.
+    pub fn kind(&self) -> LitKind {
+        match *self.0.kind() {
+            NodeKind::None => LitKind::None,
+            NodeKind::Auto => LitKind::Auto,
+            NodeKind::Bool(v) => LitKind::Bool(v),
+            NodeKind::Int(v) => LitKind::Int(v),
+            NodeKind::Float(v) => LitKind::Float(v),
+            NodeKind::Length(v, unit) => LitKind::Length(v, unit),
+            NodeKind::Angle(v, unit) => LitKind::Angle(v, unit),
+            NodeKind::Percentage(v) => LitKind::Percent(v),
+            NodeKind::Fraction(v) => LitKind::Fractional(v),
+            NodeKind::Str(ref v) => LitKind::Str(v.clone()),
+            _ => panic!("literal is of wrong kind"),
+        }
+    }
+}
+
+/// The kind of a literal.
+#[derive(Debug, Clone, PartialEq)]
+pub enum LitKind {
+    /// The none literal: `none`.
+    None,
+    /// The auto literal: `auto`.
+    Auto,
+    /// A boolean literal: `true`, `false`.
+    Bool(bool),
+    /// An integer literal: `120`.
+    Int(i64),
+    /// A floating-point literal: `1.2`, `10e-4`.
+    Float(f64),
+    /// A length literal: `12pt`, `3cm`.
+    Length(f64, LengthUnit),
+    /// An angle literal:  `1.5rad`, `90deg`.
+    Angle(f64, AngularUnit),
+    /// A percent literal: `50%`.
+    ///
+    /// _Note_: `50%` is stored as `50.0` here, but as `0.5` in the
+    /// corresponding [value](crate::geom::Relative).
+    Percent(f64),
+    /// A fraction unit literal: `1fr`.
+    Fractional(f64),
+    /// A string literal: `"hello!"`.
+    Str(EcoString),
+}
+
+node! {
+    /// An array expression: `(1, "hi", 12cm)`.
+    ArrayExpr: Array
+}
+
+impl ArrayExpr {
+    /// The array items.
+    pub fn items(&self) -> impl Iterator<Item = Expr> + '_ {
+        self.0.children().filter_map(RedRef::cast)
+    }
+}
+
+node! {
+    /// A dictionary expression: `(thickness: 3pt, pattern: dashed)`.
+    DictExpr: Dict
+}
+
+impl DictExpr {
+    /// The named dictionary items.
+    pub fn items(&self) -> impl Iterator<Item = Named> + '_ {
+        self.0.children().filter_map(RedRef::cast)
+    }
+}
+
+node! {
+    /// A pair of a name and an expression: `pattern: dashed`.
+    Named
+}
+
+impl Named {
+    /// The name: `pattern`.
+    pub fn name(&self) -> Ident {
+        self.0.cast_first_child().expect("named pair is missing name")
+    }
+
+    /// The right-hand side of the pair: `dashed`.
+    pub fn expr(&self) -> Expr {
+        self.0.cast_last_child().expect("named pair is missing expression")
+    }
+}
+
+node! {
+    /// A template expression: `[*Hi* there!]`.
+    TemplateExpr: Template
+}
+
+impl TemplateExpr {
+    /// The contents of the template.
+    pub fn body(&self) -> Markup {
+        self.0.cast_first_child().expect("template is missing body")
+    }
+}
+
+node! {
+    /// A grouped expression: `(1 + 2)`.
+    GroupExpr: Group
+}
+
+impl GroupExpr {
+    /// The wrapped expression.
+    pub fn expr(&self) -> Expr {
+        self.0.cast_first_child().expect("group is missing expression")
+    }
+}
+
+node! {
+    /// A block expression: `{ let x = 1; x + 2 }`.
+    BlockExpr: Block
+}
+
+impl BlockExpr {
+    /// The list of expressions contained in the block.
+    pub fn exprs(&self) -> impl Iterator<Item = Expr> + '_ {
+        self.0.children().filter_map(RedRef::cast)
+    }
+}
+
+node! {
+    /// A unary operation: `-x`.
+    UnaryExpr: Unary
+}
+
+impl UnaryExpr {
+    /// The operator: `-`.
+    pub fn op(&self) -> UnOp {
+        self.0
+            .children()
+            .find_map(|node| UnOp::from_token(node.kind()))
+            .expect("unary expression is missing operator")
+    }
+
+    /// The expression to operator on: `x`.
+    pub fn expr(&self) -> Expr {
+        self.0.cast_last_child().expect("unary expression is missing child")
+    }
+}
+
+/// A unary operator.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum UnOp {
+    /// The plus operator: `+`.
+    Pos,
+    /// The negation operator: `-`.
+    Neg,
+    /// The boolean `not`.
+    Not,
+}
+
+impl UnOp {
+    /// Try to convert the token into a unary operation.
+    pub fn from_token(token: &NodeKind) -> Option<Self> {
+        Some(match token {
+            NodeKind::Plus => Self::Pos,
+            NodeKind::Minus => Self::Neg,
+            NodeKind::Not => Self::Not,
+            _ => return None,
+        })
+    }
+
+    /// The precedence of this operator.
+    pub fn precedence(self) -> usize {
+        match self {
+            Self::Pos | Self::Neg => 7,
+            Self::Not => 4,
+        }
+    }
+
+    /// The string representation of this operation.
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::Pos => "+",
+            Self::Neg => "-",
+            Self::Not => "not",
+        }
+    }
+}
+
+node! {
+    /// A binary operation: `a + b`.
+    BinaryExpr: Binary
+}
+
+impl BinaryExpr {
+    /// The binary operator: `+`.
+    pub fn op(&self) -> BinOp {
+        self.0
+            .children()
+            .find_map(|node| BinOp::from_token(node.kind()))
+            .expect("binary expression is missing operator")
+    }
+
+    /// The left-hand side of the operation: `a`.
+    pub fn lhs(&self) -> Expr {
+        self.0
+            .cast_first_child()
+            .expect("binary expression is missing left-hand side")
+    }
+
+    /// The right-hand side of the operation: `b`.
+    pub fn rhs(&self) -> Expr {
+        self.0
+            .cast_last_child()
+            .expect("binary expression is missing right-hand side")
+    }
+}
+
+/// A binary operator.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum BinOp {
+    /// The addition operator: `+`.
+    Add,
+    /// The subtraction operator: `-`.
+    Sub,
+    /// The multiplication operator: `*`.
+    Mul,
+    /// The division operator: `/`.
+    Div,
+    /// The short-circuiting boolean `and`.
+    And,
+    /// The short-circuiting boolean `or`.
+    Or,
+    /// The equality operator: `==`.
+    Eq,
+    /// The inequality operator: `!=`.
+    Neq,
+    /// The less-than operator: `<`.
+    Lt,
+    /// The less-than or equal operator: `<=`.
+    Leq,
+    /// The greater-than operator: `>`.
+    Gt,
+    /// The greater-than or equal operator: `>=`.
+    Geq,
+    /// The assignment operator: `=`.
+    Assign,
+    /// The add-assign operator: `+=`.
+    AddAssign,
+    /// The subtract-assign oeprator: `-=`.
+    SubAssign,
+    /// The multiply-assign operator: `*=`.
+    MulAssign,
+    /// The divide-assign operator: `/=`.
+    DivAssign,
+}
+
+impl BinOp {
+    /// Try to convert the token into a binary operation.
+    pub fn from_token(token: &NodeKind) -> Option<Self> {
+        Some(match token {
+            NodeKind::Plus => Self::Add,
+            NodeKind::Minus => Self::Sub,
+            NodeKind::Star => Self::Mul,
+            NodeKind::Slash => Self::Div,
+            NodeKind::And => Self::And,
+            NodeKind::Or => Self::Or,
+            NodeKind::EqEq => Self::Eq,
+            NodeKind::ExclEq => Self::Neq,
+            NodeKind::Lt => Self::Lt,
+            NodeKind::LtEq => Self::Leq,
+            NodeKind::Gt => Self::Gt,
+            NodeKind::GtEq => Self::Geq,
+            NodeKind::Eq => Self::Assign,
+            NodeKind::PlusEq => Self::AddAssign,
+            NodeKind::HyphEq => Self::SubAssign,
+            NodeKind::StarEq => Self::MulAssign,
+            NodeKind::SlashEq => Self::DivAssign,
+            _ => return None,
+        })
+    }
+
+    /// The precedence of this operator.
+    pub fn precedence(self) -> usize {
+        match self {
+            Self::Mul | Self::Div => 6,
+            Self::Add | Self::Sub => 5,
+            Self::Eq | Self::Neq | Self::Lt | Self::Leq | Self::Gt | Self::Geq => 4,
+            Self::And => 3,
+            Self::Or => 2,
+            Self::Assign
+            | Self::AddAssign
+            | Self::SubAssign
+            | Self::MulAssign
+            | Self::DivAssign => 1,
+        }
+    }
+
+    /// The associativity of this operator.
+    pub fn associativity(self) -> Associativity {
+        match self {
+            Self::Add
+            | Self::Sub
+            | Self::Mul
+            | Self::Div
+            | Self::And
+            | Self::Or
+            | Self::Eq
+            | Self::Neq
+            | Self::Lt
+            | Self::Leq
+            | Self::Gt
+            | Self::Geq => Associativity::Left,
+            Self::Assign
+            | Self::AddAssign
+            | Self::SubAssign
+            | Self::MulAssign
+            | Self::DivAssign => Associativity::Right,
+        }
+    }
+
+    /// The string representation of this operation.
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::Add => "+",
+            Self::Sub => "-",
+            Self::Mul => "*",
+            Self::Div => "/",
+            Self::And => "and",
+            Self::Or => "or",
+            Self::Eq => "==",
+            Self::Neq => "!=",
+            Self::Lt => "<",
+            Self::Leq => "<=",
+            Self::Gt => ">",
+            Self::Geq => ">=",
+            Self::Assign => "=",
+            Self::AddAssign => "+=",
+            Self::SubAssign => "-=",
+            Self::MulAssign => "*=",
+            Self::DivAssign => "/=",
+        }
+    }
+}
+
+/// The associativity of a binary operator.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum Associativity {
+    /// Left-associative: `a + b + c` is equivalent to `(a + b) + c`.
+    Left,
+    /// Right-associative: `a = b = c` is equivalent to `a = (b = c)`.
+    Right,
+}
+
+node! {
+    /// An invocation of a function: `foo(...)`.
+    CallExpr: Call
+}
+
+impl CallExpr {
+    /// The function to call.
+    pub fn callee(&self) -> Expr {
+        self.0.cast_first_child().expect("call is missing callee")
+    }
+
+    /// The arguments to the function.
+    pub fn args(&self) -> CallArgs {
+        self.0.cast_last_child().expect("call is missing argument list")
+    }
+}
+
+node! {
+    /// The arguments to a function: `12, draw: false`.
+    CallArgs
+}
+
+impl CallArgs {
+    /// The positional and named arguments.
+    pub fn items(&self) -> impl Iterator<Item = CallArg> + '_ {
+        self.0.children().filter_map(RedRef::cast)
+    }
+}
+
+/// An argument to a function call.
+#[derive(Debug, Clone, PartialEq)]
+pub enum CallArg {
+    /// A positional argument: `12`.
+    Pos(Expr),
+    /// A named argument: `draw: false`.
+    Named(Named),
+    /// A spreaded argument: `..things`.
+    Spread(Expr),
+}
+
+impl TypedNode for CallArg {
+    fn from_red(node: RedRef) -> Option<Self> {
+        match node.kind() {
+            NodeKind::Named => node.cast().map(CallArg::Named),
+            NodeKind::Spread => node.cast_first_child().map(CallArg::Spread),
+            _ => node.cast().map(CallArg::Pos),
+        }
+    }
+
+    fn as_red(&self) -> RedRef<'_> {
+        match self {
+            Self::Pos(v) => v.as_red(),
+            Self::Named(v) => v.as_red(),
+            Self::Spread(v) => v.as_red(),
+        }
+    }
+}
+
+impl CallArg {
+    /// The name of this argument.
+    pub fn span(&self) -> Span {
+        match self {
+            Self::Pos(expr) => expr.span(),
+            Self::Named(named) => named.span(),
+            Self::Spread(expr) => expr.span(),
+        }
+    }
+}
+
+node! {
+    /// A closure expression: `(x, y) => z`.
+    ClosureExpr: Closure
+}
+
+impl ClosureExpr {
+    /// The name of the closure.
+    ///
+    /// This only exists if you use the function syntax sugar: `let f(x) = y`.
+    pub fn name(&self) -> Option<Ident> {
+        self.0.cast_first_child()
+    }
+
+    /// The parameter bindings.
+    pub fn params(&self) -> impl Iterator<Item = ClosureParam> + '_ {
+        self.0
+            .children()
+            .find(|x| x.kind() == &NodeKind::ClosureParams)
+            .expect("closure is missing parameter list")
+            .children()
+            .filter_map(RedRef::cast)
+    }
+
+    /// The body of the closure.
+    pub fn body(&self) -> Expr {
+        self.0.cast_last_child().expect("closure is missing body")
+    }
+}
+
+/// A parameter to a closure.
+#[derive(Debug, Clone, PartialEq)]
+pub enum ClosureParam {
+    /// A positional parameter: `x`.
+    Pos(Ident),
+    /// A named parameter with a default value: `draw: false`.
+    Named(Named),
+    /// A parameter sink: `..args`.
+    Sink(Ident),
+}
+
+impl TypedNode for ClosureParam {
+    fn from_red(node: RedRef) -> Option<Self> {
+        match node.kind() {
+            NodeKind::Ident(_) => node.cast().map(ClosureParam::Pos),
+            NodeKind::Named => node.cast().map(ClosureParam::Named),
+            NodeKind::Spread => node.cast_first_child().map(ClosureParam::Sink),
+            _ => None,
+        }
+    }
+
+    fn as_red(&self) -> RedRef<'_> {
+        match self {
+            Self::Pos(v) => v.as_red(),
+            Self::Named(v) => v.as_red(),
+            Self::Sink(v) => v.as_red(),
+        }
+    }
+}
+
+node! {
+    /// A with expression: `f with (x, y: 1)`.
+    WithExpr
+}
+
+impl WithExpr {
+    /// The function to apply the arguments to.
+    pub fn callee(&self) -> Expr {
+        self.0.cast_first_child().expect("with expression is missing callee")
+    }
+
+    /// The arguments to apply to the function.
+    pub fn args(&self) -> CallArgs {
+        self.0
+            .cast_first_child()
+            .expect("with expression is missing argument list")
+    }
+}
+
+node! {
+    /// A let expression: `let x = 1`.
+    LetExpr
+}
+
+impl LetExpr {
+    /// The binding to assign to.
+    pub fn binding(&self) -> Ident {
+        match self.0.cast_first_child() {
+            Some(Expr::Ident(binding)) => binding,
+            Some(Expr::With(with)) => match with.callee() {
+                Expr::Ident(binding) => binding,
+                _ => panic!("let .. with callee must be identifier"),
+            },
+            Some(Expr::Closure(closure)) => {
+                closure.name().expect("let-bound closure is missing name")
+            }
+            _ => panic!("let expression is missing binding"),
+        }
+    }
+
+    /// The expression the binding is initialized with.
+    pub fn init(&self) -> Option<Expr> {
+        if self.0.cast_first_child::<Ident>().is_some() {
+            self.0.children().filter_map(RedRef::cast).nth(1)
+        } else {
+            // This is a let .. with expression.
+            self.0.cast_first_child()
+        }
+    }
+}
+
+node! {
+    /// An import expression: `import a, b, c from "utils.typ"`.
+    ImportExpr
+}
+
+impl ImportExpr {
+    /// The items to be imported.
+    pub fn imports(&self) -> Imports {
+        self.0
+            .children()
+            .find_map(|node| match node.kind() {
+                NodeKind::Star => Some(Imports::Wildcard),
+                NodeKind::ImportItems => {
+                    let items = node.children().filter_map(RedRef::cast).collect();
+                    Some(Imports::Items(items))
+                }
+                _ => None,
+            })
+            .expect("import is missing items")
+    }
+
+    /// The location of the importable file.
+    pub fn path(&self) -> Expr {
+        self.0.cast_last_child().expect("import is missing path")
+    }
+}
+
+/// The items that ought to be imported from a file.
+#[derive(Debug, Clone, PartialEq)]
+pub enum Imports {
+    /// All items in the scope of the file should be imported.
+    Wildcard,
+    /// The specified items from the file should be imported.
+    Items(Vec<Ident>),
+}
+
+node! {
+    /// An include expression: `include "chapter1.typ"`.
+    IncludeExpr
+}
+
+impl IncludeExpr {
+    /// The location of the file to be included.
+    pub fn path(&self) -> Expr {
+        self.0.cast_last_child().expect("include is missing path")
+    }
+}
+
+node! {
+    /// An if-else expression: `if x { y } else { z }`.
+    IfExpr
+}
+
+impl IfExpr {
+    /// The condition which selects the body to evaluate.
+    pub fn condition(&self) -> Expr {
+        self.0.cast_first_child().expect("if expression is missing condition")
+    }
+
+    /// The expression to evaluate if the condition is true.
+    pub fn if_body(&self) -> Expr {
+        self.0
+            .children()
+            .filter_map(RedRef::cast)
+            .nth(1)
+            .expect("if expression is missing body")
+    }
+
+    /// The expression to evaluate if the condition is false.
+    pub fn else_body(&self) -> Option<Expr> {
+        self.0.children().filter_map(RedRef::cast).nth(2)
+    }
+}
+
+node! {
+    /// A while loop expression: `while x { y }`.
+    WhileExpr
+}
+
+impl WhileExpr {
+    /// The condition which selects whether to evaluate the body.
+    pub fn condition(&self) -> Expr {
+        self.0.cast_first_child().expect("while loop is missing condition")
+    }
+
+    /// The expression to evaluate while the condition is true.
+    pub fn body(&self) -> Expr {
+        self.0.cast_last_child().expect("while loop is missing body")
+    }
+}
+
+node! {
+    /// A for loop expression: `for x in y { z }`.
+    ForExpr
+}
+
+impl ForExpr {
+    /// The pattern to assign to.
+    pub fn pattern(&self) -> ForPattern {
+        self.0.cast_first_child().expect("for loop is missing pattern")
+    }
+
+    /// The expression to iterate over.
+    pub fn iter(&self) -> Expr {
+        self.0.cast_first_child().expect("for loop is missing iterable")
+    }
+
+    /// The expression to evaluate for each iteration.
+    pub fn body(&self) -> Expr {
+        self.0.cast_last_child().expect("for loop is missing body")
+    }
+}
+
+node! {
+    /// A for-in loop expression: `for x in y { z }`.
+    ForPattern
+}
+
+impl ForPattern {
+    /// The key part of the pattern: index for arrays, name for dictionaries.
+    pub fn key(&self) -> Option<Ident> {
+        let mut children = self.0.children().filter_map(RedRef::cast);
+        let key = children.next();
+        if children.next().is_some() { key } else { None }
+    }
+
+    /// The value part of the pattern.
+    pub fn value(&self) -> Ident {
+        self.0.cast_last_child().expect("for loop pattern is missing value")
+    }
+}
+
+node! {
+    /// An identifier.
+    Ident: NodeKind::Ident(_)
+}
+
+impl Ident {
+    /// Take out the contained [`EcoString`].
+    pub fn take(self) -> EcoString {
+        match self.0.green {
+            Green::Token(GreenData { kind: NodeKind::Ident(id), .. }) => id,
+            _ => panic!("identifier is of wrong kind"),
+        }
+    }
+}
+
+impl Deref for Ident {
+    type Target = str;
+
+    fn deref(&self) -> &Self::Target {
+        match &self.0.green {
+            Green::Token(GreenData { kind: NodeKind::Ident(id), .. }) => id,
+            _ => panic!("identifier is of wrong kind"),
+        }
+    }
+}
diff --git a/src/syntax/expr.rs b/src/syntax/expr.rs
deleted file mode 100644
index 904515ba..00000000
--- a/src/syntax/expr.rs
+++ /dev/null
@@ -1,584 +0,0 @@
-use std::rc::Rc;
-
-use super::{Ident, Markup, Span, Token};
-use crate::geom::{AngularUnit, LengthUnit};
-use crate::util::EcoString;
-
-/// An expression.
-#[derive(Debug, Clone, PartialEq)]
-pub enum Expr {
-    /// An identifier: `left`.
-    Ident(Box<Ident>),
-    /// A literal: `1`, `true`, ...
-    Lit(Box<Lit>),
-    /// An array expression: `(1, "hi", 12cm)`.
-    Array(Box<ArrayExpr>),
-    /// A dictionary expression: `(thickness: 3pt, pattern: dashed)`.
-    Dict(Box<DictExpr>),
-    /// A template expression: `[*Hi* there!]`.
-    Template(Box<TemplateExpr>),
-    /// A grouped expression: `(1 + 2)`.
-    Group(Box<GroupExpr>),
-    /// A block expression: `{ let x = 1; x + 2 }`.
-    Block(Box<BlockExpr>),
-    /// A unary operation: `-x`.
-    Unary(Box<UnaryExpr>),
-    /// A binary operation: `a + b`.
-    Binary(Box<BinaryExpr>),
-    /// An invocation of a function: `f(x, y)`.
-    Call(Box<CallExpr>),
-    /// A closure expression: `(x, y) => z`.
-    Closure(Box<ClosureExpr>),
-    /// A with expression: `f with (x, y: 1)`.
-    With(Box<WithExpr>),
-    /// A let expression: `let x = 1`.
-    Let(Box<LetExpr>),
-    /// An if-else expression: `if x { y } else { z }`.
-    If(Box<IfExpr>),
-    /// A while loop expression: `while x { y }`.
-    While(Box<WhileExpr>),
-    /// A for loop expression: `for x in y { z }`.
-    For(Box<ForExpr>),
-    /// An import expression: `import a, b, c from "utils.typ"`.
-    Import(Box<ImportExpr>),
-    /// An include expression: `include "chapter1.typ"`.
-    Include(Box<IncludeExpr>),
-}
-
-impl Expr {
-    /// The source code location.
-    pub fn span(&self) -> Span {
-        match self {
-            Self::Ident(v) => v.span,
-            Self::Lit(v) => v.span(),
-            Self::Array(v) => v.span,
-            Self::Dict(v) => v.span,
-            Self::Template(v) => v.span,
-            Self::Group(v) => v.span,
-            Self::Block(v) => v.span,
-            Self::Unary(v) => v.span,
-            Self::Binary(v) => v.span,
-            Self::Call(v) => v.span,
-            Self::Closure(v) => v.span,
-            Self::With(v) => v.span,
-            Self::Let(v) => v.span,
-            Self::If(v) => v.span,
-            Self::While(v) => v.span,
-            Self::For(v) => v.span,
-            Self::Import(v) => v.span,
-            Self::Include(v) => v.span,
-        }
-    }
-
-    /// Whether the expression can be shortened in markup with a hashtag.
-    pub fn has_short_form(&self) -> bool {
-        matches!(self,
-            Self::Ident(_)
-            | Self::Call(_)
-            | Self::Let(_)
-            | Self::If(_)
-            | Self::While(_)
-            | Self::For(_)
-            | Self::Import(_)
-            | Self::Include(_)
-        )
-    }
-}
-
-/// A literal: `1`, `true`, ...
-#[derive(Debug, Clone, PartialEq)]
-pub enum Lit {
-    /// The none literal: `none`.
-    None(Span),
-    /// The auto literal: `auto`.
-    Auto(Span),
-    /// A boolean literal: `true`, `false`.
-    Bool(Span, bool),
-    /// An integer literal: `120`.
-    Int(Span, i64),
-    /// A floating-point literal: `1.2`, `10e-4`.
-    Float(Span, f64),
-    /// A length literal: `12pt`, `3cm`.
-    Length(Span, f64, LengthUnit),
-    /// An angle literal:  `1.5rad`, `90deg`.
-    Angle(Span, f64, AngularUnit),
-    /// A percent literal: `50%`.
-    ///
-    /// _Note_: `50%` is stored as `50.0` here, but as `0.5` in the
-    /// corresponding [value](crate::geom::Relative).
-    Percent(Span, f64),
-    /// A fraction unit literal: `1fr`.
-    Fractional(Span, f64),
-    /// A string literal: `"hello!"`.
-    Str(Span, EcoString),
-}
-
-impl Lit {
-    /// The source code location.
-    pub fn span(&self) -> Span {
-        match *self {
-            Self::None(span) => span,
-            Self::Auto(span) => span,
-            Self::Bool(span, _) => span,
-            Self::Int(span, _) => span,
-            Self::Float(span, _) => span,
-            Self::Length(span, _, _) => span,
-            Self::Angle(span, _, _) => span,
-            Self::Percent(span, _) => span,
-            Self::Fractional(span, _) => span,
-            Self::Str(span, _) => span,
-        }
-    }
-}
-
-/// An array expression: `(1, "hi", 12cm)`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct ArrayExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The entries of the array.
-    pub items: Vec<Expr>,
-}
-
-/// A dictionary expression: `(thickness: 3pt, pattern: dashed)`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct DictExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The named dictionary entries.
-    pub items: Vec<Named>,
-}
-
-/// A pair of a name and an expression: `pattern: dashed`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct Named {
-    /// The name: `pattern`.
-    pub name: Ident,
-    /// The right-hand side of the pair: `dashed`.
-    pub expr: Expr,
-}
-
-impl Named {
-    /// The source code location.
-    pub fn span(&self) -> Span {
-        self.name.span.join(self.expr.span())
-    }
-}
-
-/// A template expression: `[*Hi* there!]`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct TemplateExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The contents of the template.
-    pub body: Markup,
-}
-
-/// A grouped expression: `(1 + 2)`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct GroupExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The wrapped expression.
-    pub expr: Expr,
-}
-
-/// A block expression: `{ let x = 1; x + 2 }`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct BlockExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The list of expressions contained in the block.
-    pub exprs: Vec<Expr>,
-}
-
-/// A unary operation: `-x`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct UnaryExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The operator: `-`.
-    pub op: UnOp,
-    /// The expression to operator on: `x`.
-    pub expr: Expr,
-}
-
-/// A unary operator.
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
-pub enum UnOp {
-    /// The plus operator: `+`.
-    Pos,
-    /// The negation operator: `-`.
-    Neg,
-    /// The boolean `not`.
-    Not,
-}
-
-impl UnOp {
-    /// Try to convert the token into a unary operation.
-    pub fn from_token(token: Token) -> Option<Self> {
-        Some(match token {
-            Token::Plus => Self::Pos,
-            Token::Hyph => Self::Neg,
-            Token::Not => Self::Not,
-            _ => return None,
-        })
-    }
-
-    /// The precedence of this operator.
-    pub fn precedence(self) -> usize {
-        match self {
-            Self::Pos | Self::Neg => 8,
-            Self::Not => 3,
-        }
-    }
-
-    /// The string representation of this operation.
-    pub fn as_str(self) -> &'static str {
-        match self {
-            Self::Pos => "+",
-            Self::Neg => "-",
-            Self::Not => "not",
-        }
-    }
-}
-
-/// A binary operation: `a + b`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct BinaryExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The left-hand side of the operation: `a`.
-    pub lhs: Expr,
-    /// The operator: `+`.
-    pub op: BinOp,
-    /// The right-hand side of the operation: `b`.
-    pub rhs: Expr,
-}
-
-/// A binary operator.
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
-pub enum BinOp {
-    /// The addition operator: `+`.
-    Add,
-    /// The subtraction operator: `-`.
-    Sub,
-    /// The multiplication operator: `*`.
-    Mul,
-    /// The division operator: `/`.
-    Div,
-    /// The short-circuiting boolean `and`.
-    And,
-    /// The short-circuiting boolean `or`.
-    Or,
-    /// The equality operator: `==`.
-    Eq,
-    /// The inequality operator: `!=`.
-    Neq,
-    /// The less-than operator: `<`.
-    Lt,
-    /// The less-than or equal operator: `<=`.
-    Leq,
-    /// The greater-than operator: `>`.
-    Gt,
-    /// The greater-than or equal operator: `>=`.
-    Geq,
-    /// The assignment operator: `=`.
-    Assign,
-    /// The add-assign operator: `+=`.
-    AddAssign,
-    /// The subtract-assign oeprator: `-=`.
-    SubAssign,
-    /// The multiply-assign operator: `*=`.
-    MulAssign,
-    /// The divide-assign operator: `/=`.
-    DivAssign,
-}
-
-impl BinOp {
-    /// Try to convert the token into a binary operation.
-    pub fn from_token(token: Token) -> Option<Self> {
-        Some(match token {
-            Token::Plus => Self::Add,
-            Token::Hyph => Self::Sub,
-            Token::Star => Self::Mul,
-            Token::Slash => Self::Div,
-            Token::And => Self::And,
-            Token::Or => Self::Or,
-            Token::EqEq => Self::Eq,
-            Token::ExclEq => Self::Neq,
-            Token::Lt => Self::Lt,
-            Token::LtEq => Self::Leq,
-            Token::Gt => Self::Gt,
-            Token::GtEq => Self::Geq,
-            Token::Eq => Self::Assign,
-            Token::PlusEq => Self::AddAssign,
-            Token::HyphEq => Self::SubAssign,
-            Token::StarEq => Self::MulAssign,
-            Token::SlashEq => Self::DivAssign,
-            _ => return None,
-        })
-    }
-
-    /// The precedence of this operator.
-    pub fn precedence(self) -> usize {
-        match self {
-            Self::Mul | Self::Div => 6,
-            Self::Add | Self::Sub => 5,
-            Self::Eq | Self::Neq | Self::Lt | Self::Leq | Self::Gt | Self::Geq => 4,
-            Self::And => 3,
-            Self::Or => 2,
-            Self::Assign
-            | Self::AddAssign
-            | Self::SubAssign
-            | Self::MulAssign
-            | Self::DivAssign => 1,
-        }
-    }
-
-    /// The associativity of this operator.
-    pub fn associativity(self) -> Associativity {
-        match self {
-            Self::Add
-            | Self::Sub
-            | Self::Mul
-            | Self::Div
-            | Self::And
-            | Self::Or
-            | Self::Eq
-            | Self::Neq
-            | Self::Lt
-            | Self::Leq
-            | Self::Gt
-            | Self::Geq => Associativity::Left,
-            Self::Assign
-            | Self::AddAssign
-            | Self::SubAssign
-            | Self::MulAssign
-            | Self::DivAssign => Associativity::Right,
-        }
-    }
-
-    /// The string representation of this operation.
-    pub fn as_str(self) -> &'static str {
-        match self {
-            Self::Add => "+",
-            Self::Sub => "-",
-            Self::Mul => "*",
-            Self::Div => "/",
-            Self::And => "and",
-            Self::Or => "or",
-            Self::Eq => "==",
-            Self::Neq => "!=",
-            Self::Lt => "<",
-            Self::Leq => "<=",
-            Self::Gt => ">",
-            Self::Geq => ">=",
-            Self::Assign => "=",
-            Self::AddAssign => "+=",
-            Self::SubAssign => "-=",
-            Self::MulAssign => "*=",
-            Self::DivAssign => "/=",
-        }
-    }
-}
-
-/// The associativity of a binary operator.
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
-pub enum Associativity {
-    /// Left-associative: `a + b + c` is equivalent to `(a + b) + c`.
-    Left,
-    /// Right-associative: `a = b = c` is equivalent to `a = (b = c)`.
-    Right,
-}
-
-/// An invocation of a function: `foo(...)`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct CallExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The function to call.
-    pub callee: Expr,
-    /// The arguments to the function.
-    pub args: CallArgs,
-}
-
-/// The arguments to a function: `12, draw: false`.
-///
-/// In case of a bracketed invocation with a body, the body is _not_
-/// included in the span for the sake of clearer error messages.
-#[derive(Debug, Clone, PartialEq)]
-pub struct CallArgs {
-    /// The source code location.
-    pub span: Span,
-    /// The positional and named arguments.
-    pub items: Vec<CallArg>,
-}
-
-/// An argument to a function call.
-#[derive(Debug, Clone, PartialEq)]
-pub enum CallArg {
-    /// A positional argument: `12`.
-    Pos(Expr),
-    /// A named argument: `draw: false`.
-    Named(Named),
-    /// A spreaded argument: `..things`.
-    Spread(Expr),
-}
-
-impl CallArg {
-    /// The source code location.
-    pub fn span(&self) -> Span {
-        match self {
-            Self::Pos(expr) => expr.span(),
-            Self::Named(named) => named.span(),
-            Self::Spread(expr) => expr.span(),
-        }
-    }
-}
-
-/// A closure expression: `(x, y) => z`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct ClosureExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The name of the closure.
-    ///
-    /// This only exists if you use the function syntax sugar: `let f(x) = y`.
-    pub name: Option<Ident>,
-    /// The parameter bindings.
-    pub params: Vec<ClosureParam>,
-    /// The body of the closure.
-    pub body: Rc<Expr>,
-}
-
-/// An parameter to a closure.
-#[derive(Debug, Clone, PartialEq)]
-pub enum ClosureParam {
-    /// A positional parameter: `x`.
-    Pos(Ident),
-    /// A named parameter with a default value: `draw: false`.
-    Named(Named),
-    /// A parameter sink: `..args`.
-    Sink(Ident),
-}
-
-impl ClosureParam {
-    /// The source code location.
-    pub fn span(&self) -> Span {
-        match self {
-            Self::Pos(ident) => ident.span,
-            Self::Named(named) => named.span(),
-            Self::Sink(ident) => ident.span,
-        }
-    }
-}
-
-/// A with expression: `f with (x, y: 1)`.
-///
-/// Applies arguments to a function.
-#[derive(Debug, Clone, PartialEq)]
-pub struct WithExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The function to apply the arguments to.
-    pub callee: Expr,
-    /// The arguments to apply to the function.
-    pub args: CallArgs,
-}
-
-/// A let expression: `let x = 1`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct LetExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The binding to assign to.
-    pub binding: Ident,
-    /// The expression the binding is initialized with.
-    pub init: Option<Expr>,
-}
-
-/// An import expression: `import a, b, c from "utils.typ"`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct ImportExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The items to be imported.
-    pub imports: Imports,
-    /// The location of the importable file.
-    pub path: Expr,
-}
-
-/// The items that ought to be imported from a file.
-#[derive(Debug, Clone, PartialEq)]
-pub enum Imports {
-    /// All items in the scope of the file should be imported.
-    Wildcard,
-    /// The specified identifiers from the file should be imported.
-    Idents(Vec<Ident>),
-}
-
-/// An include expression: `include "chapter1.typ"`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct IncludeExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The location of the file to be included.
-    pub path: Expr,
-}
-
-/// An if-else expression: `if x { y } else { z }`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct IfExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The condition which selects the body to evaluate.
-    pub condition: Expr,
-    /// The expression to evaluate if the condition is true.
-    pub if_body: Expr,
-    /// The expression to evaluate if the condition is false.
-    pub else_body: Option<Expr>,
-}
-
-/// A while loop expression: `while x { y }`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct WhileExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The condition which selects whether to evaluate the body.
-    pub condition: Expr,
-    /// The expression to evaluate while the condition is true.
-    pub body: Expr,
-}
-
-/// A for loop expression: `for x in y { z }`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct ForExpr {
-    /// The source code location.
-    pub span: Span,
-    /// The pattern to assign to.
-    pub pattern: ForPattern,
-    /// The expression to iterate over.
-    pub iter: Expr,
-    /// The expression to evaluate for each iteration.
-    pub body: Expr,
-}
-
-/// A pattern in a for loop.
-#[derive(Debug, Clone, PartialEq)]
-pub enum ForPattern {
-    /// A value pattern: `for v in array`.
-    Value(Ident),
-    /// A key-value pattern: `for k, v in dict`.
-    KeyValue(Ident, Ident),
-}
-
-impl ForPattern {
-    /// The source code location.
-    pub fn span(&self) -> Span {
-        match self {
-            Self::Value(v) => v.span,
-            Self::KeyValue(k, v) => k.span.join(v.span),
-        }
-    }
-}
diff --git a/src/syntax/ident.rs b/src/syntax/ident.rs
deleted file mode 100644
index 398e2ff9..00000000
--- a/src/syntax/ident.rs
+++ /dev/null
@@ -1,85 +0,0 @@
-use std::borrow::Borrow;
-use std::ops::Deref;
-
-use unicode_xid::UnicodeXID;
-
-use super::Span;
-use crate::util::EcoString;
-
-/// An unicode identifier with a few extra permissible characters.
-///
-/// In addition to what is specified in the [Unicode Standard][uax31], we allow:
-/// - `_` as a starting character,
-/// - `_` and `-` as continuing characters.
-///
-/// [uax31]: http://www.unicode.org/reports/tr31/
-#[derive(Debug, Clone, PartialEq)]
-pub struct Ident {
-    /// The source code location.
-    pub span: Span,
-    /// The identifier string.
-    pub string: EcoString,
-}
-
-impl Ident {
-    /// Create a new identifier from a string checking that it is a valid.
-    pub fn new(
-        string: impl AsRef<str> + Into<EcoString>,
-        span: impl Into<Span>,
-    ) -> Option<Self> {
-        if is_ident(string.as_ref()) {
-            Some(Self { span: span.into(), string: string.into() })
-        } else {
-            None
-        }
-    }
-
-    /// Return a reference to the underlying string.
-    pub fn as_str(&self) -> &str {
-        self
-    }
-}
-
-impl Deref for Ident {
-    type Target = str;
-
-    fn deref(&self) -> &Self::Target {
-        self.string.as_str()
-    }
-}
-
-impl AsRef<str> for Ident {
-    fn as_ref(&self) -> &str {
-        self
-    }
-}
-
-impl Borrow<str> for Ident {
-    fn borrow(&self) -> &str {
-        self
-    }
-}
-
-impl From<&Ident> for EcoString {
-    fn from(ident: &Ident) -> Self {
-        ident.string.clone()
-    }
-}
-
-/// Whether a string is a valid identifier.
-pub fn is_ident(string: &str) -> bool {
-    let mut chars = string.chars();
-    chars
-        .next()
-        .map_or(false, |c| is_id_start(c) && chars.all(is_id_continue))
-}
-
-/// Whether a character can start an identifier.
-pub fn is_id_start(c: char) -> bool {
-    c.is_xid_start() || c == '_'
-}
-
-/// Whether a character can continue an identifier.
-pub fn is_id_continue(c: char) -> bool {
-    c.is_xid_continue() || c == '_' || c == '-'
-}
diff --git a/src/syntax/markup.rs b/src/syntax/markup.rs
deleted file mode 100644
index 09a37116..00000000
--- a/src/syntax/markup.rs
+++ /dev/null
@@ -1,78 +0,0 @@
-use super::{Expr, Ident, Span};
-use crate::util::EcoString;
-
-/// The syntactical root capable of representing a full parsed document.
-pub type Markup = Vec<MarkupNode>;
-
-/// A single piece of markup.
-#[derive(Debug, Clone, PartialEq)]
-pub enum MarkupNode {
-    /// Whitespace containing less than two newlines.
-    Space,
-    /// A forced line break: `\`.
-    Linebreak(Span),
-    /// A paragraph break: Two or more newlines.
-    Parbreak(Span),
-    /// Strong text was enabled / disabled: `*`.
-    Strong(Span),
-    /// Emphasized text was enabled / disabled: `_`.
-    Emph(Span),
-    /// Plain text.
-    Text(EcoString),
-    /// A raw block with optional syntax highlighting: `` `...` ``.
-    Raw(Box<RawNode>),
-    /// A section heading: `= Introduction`.
-    Heading(Box<HeadingNode>),
-    /// An item in an unordered list: `- ...`.
-    List(Box<ListNode>),
-    /// An item in an enumeration (ordered list): `1. ...`.
-    Enum(Box<EnumNode>),
-    /// An expression.
-    Expr(Expr),
-}
-
-/// A raw block with optional syntax highlighting: `` `...` ``.
-#[derive(Debug, Clone, PartialEq)]
-pub struct RawNode {
-    /// The source code location.
-    pub span: Span,
-    /// An optional identifier specifying the language to syntax-highlight in.
-    pub lang: Option<Ident>,
-    /// The raw text, determined as the raw string between the backticks trimmed
-    /// according to the above rules.
-    pub text: EcoString,
-    /// Whether the element is block-level, that is, it has 3+ backticks
-    /// and contains at least one newline.
-    pub block: bool,
-}
-
-/// A section heading: `= Introduction`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct HeadingNode {
-    /// The source code location.
-    pub span: Span,
-    /// The section depth (numer of equals signs).
-    pub level: usize,
-    /// The contents of the heading.
-    pub body: Markup,
-}
-
-/// An item in an unordered list: `- ...`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct ListNode {
-    /// The source code location.
-    pub span: Span,
-    /// The contents of the list item.
-    pub body: Markup,
-}
-
-/// An item in an enumeration (ordered list): `1. ...`.
-#[derive(Debug, Clone, PartialEq)]
-pub struct EnumNode {
-    /// The source code location.
-    pub span: Span,
-    /// The number, if any.
-    pub number: Option<usize>,
-    /// The contents of the list item.
-    pub body: Markup,
-}
diff --git a/src/syntax/mod.rs b/src/syntax/mod.rs
index 8dbb108d..ca6ed243 100644
--- a/src/syntax/mod.rs
+++ b/src/syntax/mod.rs
@@ -1,16 +1,747 @@
 //! Syntax types.
 
-mod expr;
-mod ident;
-mod markup;
+pub mod ast;
 mod pretty;
 mod span;
-mod token;
-pub mod visit;
 
-pub use expr::*;
-pub use ident::*;
-pub use markup::*;
+use std::fmt::{self, Debug, Display, Formatter};
+use std::rc::Rc;
+
 pub use pretty::*;
 pub use span::*;
-pub use token::*;
+
+use self::ast::{MathNode, RawNode, TypedNode};
+use crate::diag::Error;
+use crate::geom::{AngularUnit, LengthUnit};
+use crate::source::SourceId;
+use crate::util::EcoString;
+
+/// An inner of leaf node in the untyped green tree.
+#[derive(Clone, PartialEq)]
+pub enum Green {
+    /// A reference-counted inner node.
+    Node(Rc<GreenNode>),
+    /// A terminal, owned token.
+    Token(GreenData),
+}
+
+impl Green {
+    /// Returns the metadata of the node.
+    fn data(&self) -> &GreenData {
+        match self {
+            Green::Node(n) => &n.data,
+            Green::Token(t) => &t,
+        }
+    }
+
+    /// The type of the node.
+    pub fn kind(&self) -> &NodeKind {
+        self.data().kind()
+    }
+
+    /// The length of the node.
+    pub fn len(&self) -> usize {
+        self.data().len()
+    }
+
+    /// Whether the node or its children contain an error.
+    pub fn erroneous(&self) -> bool {
+        match self {
+            Self::Node(node) => node.erroneous,
+            Self::Token(data) => data.kind.is_error(),
+        }
+    }
+
+    /// The node's children.
+    pub fn children(&self) -> &[Green] {
+        match self {
+            Green::Node(n) => &n.children(),
+            Green::Token(_) => &[],
+        }
+    }
+
+    /// Change the type of the node.
+    pub fn convert(&mut self, kind: NodeKind) {
+        match self {
+            Self::Node(node) => {
+                let node = Rc::make_mut(node);
+                node.erroneous |= kind.is_error();
+                node.data.kind = kind;
+            }
+            Self::Token(data) => data.kind = kind,
+        }
+    }
+}
+
+impl Default for Green {
+    fn default() -> Self {
+        Self::Token(GreenData::new(NodeKind::None, 0))
+    }
+}
+
+impl Debug for Green {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "{:?}: {}", self.kind(), self.len())?;
+        if let Self::Node(n) = self {
+            if !n.children.is_empty() {
+                f.write_str(" ")?;
+                f.debug_list().entries(&n.children).finish()?;
+            }
+        }
+        Ok(())
+    }
+}
+
+/// An inner node in the untyped green tree.
+#[derive(Debug, Clone, PartialEq)]
+pub struct GreenNode {
+    /// Node metadata.
+    data: GreenData,
+    /// This node's children, losslessly make up this node.
+    children: Vec<Green>,
+    /// Whether this node or any of its children are erroneous.
+    erroneous: bool,
+}
+
+impl GreenNode {
+    /// Creates a new node with the given kind and a single child.
+    pub fn with_child(kind: NodeKind, child: impl Into<Green>) -> Self {
+        Self::with_children(kind, vec![child.into()])
+    }
+
+    /// Creates a new node with the given kind and children.
+    pub fn with_children(kind: NodeKind, children: Vec<Green>) -> Self {
+        let mut erroneous = kind.is_error();
+        let len = children
+            .iter()
+            .inspect(|c| erroneous |= c.erroneous())
+            .map(Green::len)
+            .sum();
+
+        Self {
+            data: GreenData::new(kind, len),
+            children,
+            erroneous,
+        }
+    }
+
+    /// The node's children.
+    pub fn children(&self) -> &[Green] {
+        &self.children
+    }
+}
+
+impl From<GreenNode> for Green {
+    fn from(node: GreenNode) -> Self {
+        Rc::new(node).into()
+    }
+}
+
+impl From<Rc<GreenNode>> for Green {
+    fn from(node: Rc<GreenNode>) -> Self {
+        Self::Node(node)
+    }
+}
+
+/// Data shared between inner and leaf nodes.
+#[derive(Debug, Clone, PartialEq)]
+pub struct GreenData {
+    /// What kind of node this is (each kind would have its own struct in a
+    /// strongly typed AST).
+    kind: NodeKind,
+    /// The byte length of the node in the source.
+    len: usize,
+}
+
+impl GreenData {
+    /// Create new node metadata.
+    pub fn new(kind: NodeKind, len: usize) -> Self {
+        Self { len, kind }
+    }
+
+    /// The type of the node.
+    pub fn kind(&self) -> &NodeKind {
+        &self.kind
+    }
+
+    /// The length of the node.
+    pub fn len(&self) -> usize {
+        self.len
+    }
+}
+
+impl From<GreenData> for Green {
+    fn from(token: GreenData) -> Self {
+        Self::Token(token)
+    }
+}
+
+/// A owned wrapper for a green node with span information.
+///
+/// Owned variant of [`RedRef`]. Can be [cast](Self::cast) to an AST node.
+#[derive(Clone, PartialEq)]
+pub struct RedNode {
+    id: SourceId,
+    offset: usize,
+    green: Green,
+}
+
+impl RedNode {
+    /// Create a new red node from a root [`GreenNode`].
+    pub fn from_root(root: Rc<GreenNode>, id: SourceId) -> Self {
+        Self { id, offset: 0, green: root.into() }
+    }
+
+    /// Convert to a borrowed representation.
+    pub fn as_ref(&self) -> RedRef<'_> {
+        RedRef {
+            id: self.id,
+            offset: self.offset,
+            green: &self.green,
+        }
+    }
+
+    /// The type of the node.
+    pub fn kind(&self) -> &NodeKind {
+        self.as_ref().kind()
+    }
+
+    /// The length of the node.
+    pub fn len(&self) -> usize {
+        self.as_ref().len()
+    }
+
+    /// The span of the node.
+    pub fn span(&self) -> Span {
+        self.as_ref().span()
+    }
+
+    /// The error messages for this node and its descendants.
+    pub fn errors(&self) -> Vec<Error> {
+        self.as_ref().errors()
+    }
+
+    /// Convert the node to a typed AST node.
+    pub fn cast<T>(self) -> Option<T>
+    where
+        T: TypedNode,
+    {
+        self.as_ref().cast()
+    }
+
+    /// The children of the node.
+    pub fn children(&self) -> Children<'_> {
+        self.as_ref().children()
+    }
+
+    /// Get the first child that can cast to some AST type.
+    pub fn cast_first_child<T: TypedNode>(&self) -> Option<T> {
+        self.as_ref().cast_first_child()
+    }
+
+    /// Get the last child that can cast to some AST type.
+    pub fn cast_last_child<T: TypedNode>(&self) -> Option<T> {
+        self.as_ref().cast_last_child()
+    }
+}
+
+impl Debug for RedNode {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        self.as_ref().fmt(f)
+    }
+}
+
+/// A borrowed wrapper for a green node with span information.
+///
+/// Borrowed variant of [`RedNode`]. Can be [cast](Self::cast) to an AST node.
+#[derive(Copy, Clone, PartialEq)]
+pub struct RedRef<'a> {
+    id: SourceId,
+    offset: usize,
+    green: &'a Green,
+}
+
+impl<'a> RedRef<'a> {
+    /// Convert to an owned representation.
+    pub fn own(self) -> RedNode {
+        RedNode {
+            id: self.id,
+            offset: self.offset,
+            green: self.green.clone(),
+        }
+    }
+
+    /// The type of the node.
+    pub fn kind(self) -> &'a NodeKind {
+        self.green.kind()
+    }
+
+    /// The length of the node.
+    pub fn len(self) -> usize {
+        self.green.len()
+    }
+
+    /// The span of the node.
+    pub fn span(self) -> Span {
+        Span::new(self.id, self.offset, self.offset + self.green.len())
+    }
+
+    /// The error messages for this node and its descendants.
+    pub fn errors(self) -> Vec<Error> {
+        if !self.green.erroneous() {
+            return vec![];
+        }
+
+        match self.kind() {
+            NodeKind::Error(pos, msg) => {
+                let span = match pos {
+                    ErrorPos::Start => self.span().at_start(),
+                    ErrorPos::Full => self.span(),
+                    ErrorPos::End => self.span().at_end(),
+                };
+
+                vec![Error::new(span, msg.to_string())]
+            }
+            _ => self
+                .children()
+                .filter(|red| red.green.erroneous())
+                .flat_map(|red| red.errors())
+                .collect(),
+        }
+    }
+
+    /// Convert the node to a typed AST node.
+    pub fn cast<T>(self) -> Option<T>
+    where
+        T: TypedNode,
+    {
+        T::from_red(self)
+    }
+
+    /// The node's children.
+    pub fn children(self) -> Children<'a> {
+        let children = match &self.green {
+            Green::Node(node) => node.children(),
+            Green::Token(_) => &[],
+        };
+
+        Children {
+            id: self.id,
+            iter: children.iter(),
+            front: self.offset,
+            back: self.offset + self.len(),
+        }
+    }
+
+    /// Get the first child that can cast to some AST type.
+    pub fn cast_first_child<T: TypedNode>(self) -> Option<T> {
+        self.children().find_map(RedRef::cast)
+    }
+
+    /// Get the last child that can cast to some AST type.
+    pub fn cast_last_child<T: TypedNode>(self) -> Option<T> {
+        self.children().rev().find_map(RedRef::cast)
+    }
+}
+
+impl Debug for RedRef<'_> {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "{:?}: {:?}", self.kind(), self.span())?;
+        let mut children = self.children().peekable();
+        if children.peek().is_some() {
+            f.write_str(" ")?;
+            f.debug_list().entries(children.map(RedRef::own)).finish()?;
+        }
+        Ok(())
+    }
+}
+
+/// An iterator over the children of a red node.
+pub struct Children<'a> {
+    id: SourceId,
+    iter: std::slice::Iter<'a, Green>,
+    front: usize,
+    back: usize,
+}
+
+impl<'a> Iterator for Children<'a> {
+    type Item = RedRef<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.iter.next().map(|green| {
+            let offset = self.front;
+            self.front += green.len();
+            RedRef { id: self.id, offset, green }
+        })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+impl DoubleEndedIterator for Children<'_> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.iter.next_back().map(|green| {
+            self.back -= green.len();
+            RedRef { id: self.id, offset: self.back, green }
+        })
+    }
+}
+
+impl ExactSizeIterator for Children<'_> {}
+
+/// All syntactical building blocks that can be part of a Typst document.
+///
+/// Can be emitted as a token by the tokenizer or as part of a green node by
+/// the parser.
+#[derive(Debug, Clone, PartialEq)]
+pub enum NodeKind {
+    /// A left square bracket: `[`.
+    LeftBracket,
+    /// A right square bracket: `]`.
+    RightBracket,
+    /// A left curly brace: `{`.
+    LeftBrace,
+    /// A right curly brace: `}`.
+    RightBrace,
+    /// A left round parenthesis: `(`.
+    LeftParen,
+    /// A right round parenthesis: `)`.
+    RightParen,
+    /// An asterisk: `*`.
+    Star,
+    /// A comma: `,`.
+    Comma,
+    /// A semicolon: `;`.
+    Semicolon,
+    /// A colon: `:`.
+    Colon,
+    /// A plus: `+`.
+    Plus,
+    /// A hyphen: `-`.
+    Minus,
+    /// A slash: `/`.
+    Slash,
+    /// A single equals sign: `=`.
+    Eq,
+    /// Two equals signs: `==`.
+    EqEq,
+    /// An exclamation mark followed by an equals sign: `!=`.
+    ExclEq,
+    /// A less-than sign: `<`.
+    Lt,
+    /// A less-than sign followed by an equals sign: `<=`.
+    LtEq,
+    /// A greater-than sign: `>`.
+    Gt,
+    /// A greater-than sign followed by an equals sign: `>=`.
+    GtEq,
+    /// A plus followed by an equals sign: `+=`.
+    PlusEq,
+    /// A hyphen followed by an equals sign: `-=`.
+    HyphEq,
+    /// An asterisk followed by an equals sign: `*=`.
+    StarEq,
+    /// A slash followed by an equals sign: `/=`.
+    SlashEq,
+    /// The `not` operator.
+    Not,
+    /// The `and` operator.
+    And,
+    /// The `or` operator.
+    Or,
+    /// The `with` operator.
+    With,
+    /// Two dots: `..`.
+    Dots,
+    /// An equals sign followed by a greater-than sign: `=>`.
+    Arrow,
+    /// The none literal: `none`.
+    None,
+    /// The auto literal: `auto`.
+    Auto,
+    /// The `let` keyword.
+    Let,
+    /// The `if` keyword.
+    If,
+    /// The `else` keyword.
+    Else,
+    /// The `for` keyword.
+    For,
+    /// The `in` keyword.
+    In,
+    /// The `while` keyword.
+    While,
+    /// The `break` keyword.
+    Break,
+    /// The `continue` keyword.
+    Continue,
+    /// The `return` keyword.
+    Return,
+    /// The `import` keyword.
+    Import,
+    /// The `include` keyword.
+    Include,
+    /// The `from` keyword.
+    From,
+    /// Template markup.
+    Markup,
+    /// One or more whitespace characters.
+    Space(usize),
+    /// A forced line break: `\`.
+    Linebreak,
+    /// A paragraph break: Two or more newlines.
+    Parbreak,
+    /// A consecutive non-markup string.
+    Text(EcoString),
+    /// A non-breaking space: `~`.
+    NonBreakingSpace,
+    /// An en-dash: `--`.
+    EnDash,
+    /// An em-dash: `---`.
+    EmDash,
+    /// A slash and the letter "u" followed by a hexadecimal unicode entity
+    /// enclosed in curly braces: `\u{1F5FA}`.
+    UnicodeEscape(char),
+    /// Strong text was enabled / disabled: `*`.
+    Strong,
+    /// Emphasized text was enabled / disabled: `_`.
+    Emph,
+    /// A section heading: `= Introduction`.
+    Heading,
+    /// An item in an enumeration (ordered list): `1. ...`.
+    Enum,
+    /// A numbering: `23.`.
+    ///
+    /// Can also exist without the number: `.`.
+    EnumNumbering(Option<usize>),
+    /// An item in an unordered list: `- ...`.
+    List,
+    /// An arbitrary number of backticks followed by inner contents, terminated
+    /// with the same number of backticks: `` `...` ``.
+    Raw(Rc<RawNode>),
+    /// Dollar signs surrounding inner contents.
+    Math(Rc<MathNode>),
+    /// An identifier: `center`.
+    Ident(EcoString),
+    /// A boolean: `true`, `false`.
+    Bool(bool),
+    /// An integer: `120`.
+    Int(i64),
+    /// A floating-point number: `1.2`, `10e-4`.
+    Float(f64),
+    /// A length: `12pt`, `3cm`.
+    Length(f64, LengthUnit),
+    /// An angle: `90deg`.
+    Angle(f64, AngularUnit),
+    /// A percentage: `50%`.
+    ///
+    /// _Note_: `50%` is stored as `50.0` here, as in the corresponding
+    /// [literal](ast::LitKind::Percent).
+    Percentage(f64),
+    /// A fraction unit: `3fr`.
+    Fraction(f64),
+    /// A quoted string: `"..."`.
+    Str(EcoString),
+    /// An array expression: `(1, "hi", 12cm)`.
+    Array,
+    /// A dictionary expression: `(thickness: 3pt, pattern: dashed)`.
+    Dict,
+    /// A named pair: `thickness: 3pt`.
+    Named,
+    /// A grouped expression: `(1 + 2)`.
+    Group,
+    /// A unary operation: `-x`.
+    Unary,
+    /// A binary operation: `a + b`.
+    Binary,
+    /// An invocation of a function: `f(x, y)`.
+    Call,
+    /// A function call's argument list: `(x, y)`.
+    CallArgs,
+    /// A closure expression: `(x, y) => z`.
+    Closure,
+    /// A closure's parameters: `(x, y)`.
+    ClosureParams,
+    /// A parameter sink: `..x`.
+    Spread,
+    /// A template expression: `[*Hi* there!]`.
+    Template,
+    /// A block expression: `{ let x = 1; x + 2 }`.
+    Block,
+    /// A for loop expression: `for x in y { ... }`.
+    ForExpr,
+    /// A while loop expression: `while x { ... }`.
+    WhileExpr,
+    /// An if expression: `if x { ... }`.
+    IfExpr,
+    /// A let expression: `let x = 1`.
+    LetExpr,
+    /// The `with` expression: `with (1)`.
+    WithExpr,
+    /// A for loop's destructuring pattern: `x` or `x, y`.
+    ForPattern,
+    /// The import expression: `import x from "foo.typ"`.
+    ImportExpr,
+    /// Items to import: `a, b, c`.
+    ImportItems,
+    /// The include expression: `include "foo.typ"`.
+    IncludeExpr,
+    /// Two slashes followed by inner contents, terminated with a newline:
+    /// `//<str>\n`.
+    LineComment,
+    /// A slash and a star followed by inner contents,  terminated with a star
+    /// and a slash: `/*<str>*/`.
+    ///
+    /// The comment can contain nested block comments.
+    BlockComment,
+    /// Tokens that appear in the wrong place.
+    Error(ErrorPos, EcoString),
+    /// Unknown character sequences.
+    Unknown(EcoString),
+}
+
+/// Where in a node an error should be annotated.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum ErrorPos {
+    /// At the start of the node.
+    Start,
+    /// Over the full width of the node.
+    Full,
+    /// At the end of the node.
+    End,
+}
+
+impl NodeKind {
+    /// Whether this is some kind of parenthesis.
+    pub fn is_paren(&self) -> bool {
+        matches!(self, Self::LeftParen | Self::RightParen)
+    }
+
+    /// Whether this is some kind of bracket.
+    pub fn is_bracket(&self) -> bool {
+        matches!(self, Self::LeftBracket | Self::RightBracket)
+    }
+
+    /// Whether this is some kind of brace.
+    pub fn is_brace(&self) -> bool {
+        matches!(self, Self::LeftBrace | Self::RightBrace)
+    }
+
+    /// Whether this is some kind of error.
+    pub fn is_error(&self) -> bool {
+        matches!(self, NodeKind::Error(_, _) | NodeKind::Unknown(_))
+    }
+
+    /// A human-readable name for the kind.
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            Self::LeftBracket => "opening bracket",
+            Self::RightBracket => "closing bracket",
+            Self::LeftBrace => "opening brace",
+            Self::RightBrace => "closing brace",
+            Self::LeftParen => "opening paren",
+            Self::RightParen => "closing paren",
+            Self::Star => "star",
+            Self::Comma => "comma",
+            Self::Semicolon => "semicolon",
+            Self::Colon => "colon",
+            Self::Plus => "plus",
+            Self::Minus => "minus",
+            Self::Slash => "slash",
+            Self::Eq => "assignment operator",
+            Self::EqEq => "equality operator",
+            Self::ExclEq => "inequality operator",
+            Self::Lt => "less-than operator",
+            Self::LtEq => "less-than or equal operator",
+            Self::Gt => "greater-than operator",
+            Self::GtEq => "greater-than or equal operator",
+            Self::PlusEq => "add-assign operator",
+            Self::HyphEq => "subtract-assign operator",
+            Self::StarEq => "multiply-assign operator",
+            Self::SlashEq => "divide-assign operator",
+            Self::Not => "operator `not`",
+            Self::And => "operator `and`",
+            Self::Or => "operator `or`",
+            Self::With => "operator `with`",
+            Self::Dots => "dots",
+            Self::Arrow => "arrow",
+            Self::None => "`none`",
+            Self::Auto => "`auto`",
+            Self::Let => "keyword `let`",
+            Self::If => "keyword `if`",
+            Self::Else => "keyword `else`",
+            Self::For => "keyword `for`",
+            Self::In => "keyword `in`",
+            Self::While => "keyword `while`",
+            Self::Break => "keyword `break`",
+            Self::Continue => "keyword `continue`",
+            Self::Return => "keyword `return`",
+            Self::Import => "keyword `import`",
+            Self::Include => "keyword `include`",
+            Self::From => "keyword `from`",
+            Self::Markup => "markup",
+            Self::Space(_) => "space",
+            Self::Linebreak => "forced linebreak",
+            Self::Parbreak => "paragraph break",
+            Self::Text(_) => "text",
+            Self::NonBreakingSpace => "non-breaking space",
+            Self::EnDash => "en dash",
+            Self::EmDash => "em dash",
+            Self::UnicodeEscape(_) => "unicode escape sequence",
+            Self::Strong => "strong",
+            Self::Emph => "emphasis",
+            Self::Heading => "heading",
+            Self::Enum => "enumeration item",
+            Self::EnumNumbering(_) => "enumeration item numbering",
+            Self::List => "list item",
+            Self::Raw(_) => "raw block",
+            Self::Math(_) => "math formula",
+            Self::Ident(_) => "identifier",
+            Self::Bool(_) => "boolean",
+            Self::Int(_) => "integer",
+            Self::Float(_) => "float",
+            Self::Length(_, _) => "length",
+            Self::Angle(_, _) => "angle",
+            Self::Percentage(_) => "percentage",
+            Self::Fraction(_) => "`fr` value",
+            Self::Str(_) => "string",
+            Self::Array => "array",
+            Self::Dict => "dictionary",
+            Self::Named => "named argument",
+            Self::Group => "group",
+            Self::Unary => "unary expression",
+            Self::Binary => "binary expression",
+            Self::Call => "call",
+            Self::CallArgs => "call arguments",
+            Self::Closure => "closure",
+            Self::ClosureParams => "closure parameters",
+            Self::Spread => "parameter sink",
+            Self::Template => "template",
+            Self::Block => "block",
+            Self::ForExpr => "for-loop expression",
+            Self::WhileExpr => "while-loop expression",
+            Self::IfExpr => "`if` expression",
+            Self::LetExpr => "`let` expression",
+            Self::WithExpr => "`with` expression",
+            Self::ForPattern => "for-loop destructuring pattern",
+            Self::ImportExpr => "`import` expression",
+            Self::ImportItems => "import items",
+            Self::IncludeExpr => "`include` expression",
+            Self::LineComment => "line comment",
+            Self::BlockComment => "block comment",
+            Self::Error(_, _) => "parse error",
+            Self::Unknown(src) => match src.as_str() {
+                "*/" => "end of block comment",
+                _ => "invalid token",
+            },
+        }
+    }
+}
+
+impl Display for NodeKind {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        f.pad(self.as_str())
+    }
+}
diff --git a/src/syntax/pretty.rs b/src/syntax/pretty.rs
index 3d02f39f..c453fb56 100644
--- a/src/syntax/pretty.rs
+++ b/src/syntax/pretty.rs
@@ -2,7 +2,7 @@
 
 use std::fmt::{self, Arguments, Write};
 
-use super::*;
+use super::ast::*;
 
 /// Pretty print an item and return the resulting string.
 pub fn pretty<T>(item: &T) -> String
@@ -46,20 +46,24 @@ impl Printer {
         Write::write_fmt(self, fmt)
     }
 
-    /// Write a list of items joined by a joiner.
-    pub fn join<T, I, F>(&mut self, items: I, joiner: &str, mut write_item: F)
+    /// Write a list of items joined by a joiner and return how many there were.
+    pub fn join<T, I, F>(&mut self, items: I, joiner: &str, mut write_item: F) -> usize
     where
         I: IntoIterator<Item = T>,
         F: FnMut(T, &mut Self),
     {
+        let mut count = 0;
         let mut iter = items.into_iter();
         if let Some(first) = iter.next() {
             write_item(first, self);
+            count += 1;
         }
         for item in iter {
             self.push_str(joiner);
             write_item(item, self);
+            count += 1;
         }
+        count
     }
 
     /// Finish pretty printing and return the underlying buffer.
@@ -77,7 +81,7 @@ impl Write for Printer {
 
 impl Pretty for Markup {
     fn pretty(&self, p: &mut Printer) {
-        for node in self {
+        for node in self.nodes() {
             node.pretty(p);
         }
     }
@@ -88,12 +92,13 @@ impl Pretty for MarkupNode {
         match self {
             // TODO: Handle escaping.
             Self::Space => p.push(' '),
-            Self::Linebreak(_) => p.push_str(r"\"),
-            Self::Parbreak(_) => p.push_str("\n\n"),
-            Self::Strong(_) => p.push('*'),
-            Self::Emph(_) => p.push('_'),
+            Self::Linebreak => p.push_str(r"\"),
+            Self::Parbreak => p.push_str("\n\n"),
+            Self::Strong => p.push('*'),
+            Self::Emph => p.push('_'),
             Self::Text(text) => p.push_str(text),
             Self::Raw(raw) => raw.pretty(p),
+            Self::Math(math) => math.pretty(p),
             Self::Heading(heading) => heading.pretty(p),
             Self::List(list) => list.pretty(p),
             Self::Enum(enum_) => enum_.pretty(p),
@@ -136,7 +141,7 @@ impl Pretty for RawNode {
 
         // Language tag.
         if let Some(lang) = &self.lang {
-            lang.pretty(p);
+            p.push_str(lang);
         }
 
         // Start untrimming.
@@ -163,38 +168,52 @@ impl Pretty for RawNode {
     }
 }
 
+impl Pretty for MathNode {
+    fn pretty(&self, p: &mut Printer) {
+        p.push('$');
+        if self.display {
+            p.push('[');
+        }
+        p.push_str(&self.formula);
+        if self.display {
+            p.push(']');
+        }
+        p.push('$');
+    }
+}
+
 impl Pretty for HeadingNode {
     fn pretty(&self, p: &mut Printer) {
-        for _ in 0 .. self.level {
+        for _ in 0 .. self.level() {
             p.push('=');
         }
         p.push(' ');
-        self.body.pretty(p);
+        self.body().pretty(p);
     }
 }
 
 impl Pretty for ListNode {
     fn pretty(&self, p: &mut Printer) {
         p.push_str("- ");
-        self.body.pretty(p);
+        self.body().pretty(p);
     }
 }
 
 impl Pretty for EnumNode {
     fn pretty(&self, p: &mut Printer) {
-        if let Some(number) = self.number {
+        if let Some(number) = self.number() {
             write!(p, "{}", number).unwrap();
         }
         p.push_str(". ");
-        self.body.pretty(p);
+        self.body().pretty(p);
     }
 }
 
 impl Pretty for Expr {
     fn pretty(&self, p: &mut Printer) {
         match self {
-            Self::Ident(v) => v.pretty(p),
             Self::Lit(v) => v.pretty(p),
+            Self::Ident(v) => v.pretty(p),
             Self::Array(v) => v.pretty(p),
             Self::Dict(v) => v.pretty(p),
             Self::Template(v) => v.pretty(p),
@@ -217,17 +236,17 @@ impl Pretty for Expr {
 
 impl Pretty for Lit {
     fn pretty(&self, p: &mut Printer) {
-        match self {
-            Self::None(_) => p.push_str("none"),
-            Self::Auto(_) => p.push_str("auto"),
-            Self::Bool(_, v) => write!(p, "{}", v).unwrap(),
-            Self::Int(_, v) => write!(p, "{}", v).unwrap(),
-            Self::Float(_, v) => write!(p, "{}", v).unwrap(),
-            Self::Length(_, v, u) => write!(p, "{}{:?}", v, u).unwrap(),
-            Self::Angle(_, v, u) => write!(p, "{}{:?}", v, u).unwrap(),
-            Self::Percent(_, v) => write!(p, "{}%", v).unwrap(),
-            Self::Fractional(_, v) => write!(p, "{}fr", v).unwrap(),
-            Self::Str(_, v) => write!(p, "{:?}", v).unwrap(),
+        match self.kind() {
+            LitKind::None => p.push_str("none"),
+            LitKind::Auto => p.push_str("auto"),
+            LitKind::Bool(v) => write!(p, "{}", v).unwrap(),
+            LitKind::Int(v) => write!(p, "{}", v).unwrap(),
+            LitKind::Float(v) => write!(p, "{}", v).unwrap(),
+            LitKind::Length(v, u) => write!(p, "{}{:?}", v, u).unwrap(),
+            LitKind::Angle(v, u) => write!(p, "{}{:?}", v, u).unwrap(),
+            LitKind::Percent(v) => write!(p, "{}%", v).unwrap(),
+            LitKind::Fractional(v) => write!(p, "{}fr", v).unwrap(),
+            LitKind::Str(v) => write!(p, "{:?}", v).unwrap(),
         }
     }
 }
@@ -235,8 +254,10 @@ impl Pretty for Lit {
 impl Pretty for ArrayExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push('(');
-        p.join(&self.items, ", ", |item, p| item.pretty(p));
-        if self.items.len() == 1 {
+
+        let items = self.items();
+        let len = p.join(items, ", ", |item, p| item.pretty(p));
+        if len == 1 {
             p.push(',');
         }
         p.push(')');
@@ -246,10 +267,9 @@ impl Pretty for ArrayExpr {
 impl Pretty for DictExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push('(');
-        if self.items.is_empty() {
+        let len = p.join(self.items(), ", ", |named, p| named.pretty(p));
+        if len == 0 {
             p.push(':');
-        } else {
-            p.join(&self.items, ", ", |named, p| named.pretty(p));
         }
         p.push(')');
     }
@@ -257,16 +277,16 @@ impl Pretty for DictExpr {
 
 impl Pretty for Named {
     fn pretty(&self, p: &mut Printer) {
-        self.name.pretty(p);
+        self.name().pretty(p);
         p.push_str(": ");
-        self.expr.pretty(p);
+        self.expr().pretty(p);
     }
 }
 
 impl Pretty for TemplateExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push('[');
-        self.body.pretty(p);
+        self.body().pretty(p);
         p.push(']');
     }
 }
@@ -274,7 +294,7 @@ impl Pretty for TemplateExpr {
 impl Pretty for GroupExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push('(');
-        self.expr.pretty(p);
+        self.expr().pretty(p);
         p.push(')');
     }
 }
@@ -282,11 +302,11 @@ impl Pretty for GroupExpr {
 impl Pretty for BlockExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push('{');
-        if self.exprs.len() > 1 {
+        if self.exprs().count() > 1 {
             p.push(' ');
         }
-        p.join(&self.exprs, "; ", |expr, p| expr.pretty(p));
-        if self.exprs.len() > 1 {
+        let len = p.join(self.exprs(), "; ", |expr, p| expr.pretty(p));
+        if len > 1 {
             p.push(' ');
         }
         p.push('}');
@@ -295,11 +315,12 @@ impl Pretty for BlockExpr {
 
 impl Pretty for UnaryExpr {
     fn pretty(&self, p: &mut Printer) {
-        self.op.pretty(p);
-        if self.op == UnOp::Not {
+        let op = self.op();
+        op.pretty(p);
+        if op == UnOp::Not {
             p.push(' ');
         }
-        self.expr.pretty(p);
+        self.expr().pretty(p);
     }
 }
 
@@ -311,11 +332,11 @@ impl Pretty for UnOp {
 
 impl Pretty for BinaryExpr {
     fn pretty(&self, p: &mut Printer) {
-        self.lhs.pretty(p);
+        self.lhs().pretty(p);
         p.push(' ');
-        self.op.pretty(p);
+        self.op().pretty(p);
         p.push(' ');
-        self.rhs.pretty(p);
+        self.rhs().pretty(p);
     }
 }
 
@@ -327,7 +348,7 @@ impl Pretty for BinOp {
 
 impl Pretty for CallExpr {
     fn pretty(&self, p: &mut Printer) {
-        self.callee.pretty(p);
+        self.callee().pretty(p);
 
         let mut write_args = |items: &[CallArg]| {
             p.push('(');
@@ -335,7 +356,8 @@ impl Pretty for CallExpr {
             p.push(')');
         };
 
-        match self.args.items.as_slice() {
+        let args: Vec<_> = self.args().items().collect();
+        match args.as_slice() {
             // This can be moved behind the arguments.
             //
             // Example: Transforms "#v(a, [b])" => "#v(a)[b]".
@@ -345,7 +367,6 @@ impl Pretty for CallExpr {
                 }
                 template.pretty(p);
             }
-
             items => write_args(items),
         }
     }
@@ -353,7 +374,7 @@ impl Pretty for CallExpr {
 
 impl Pretty for CallArgs {
     fn pretty(&self, p: &mut Printer) {
-        p.join(&self.items, ", ", |item, p| item.pretty(p));
+        p.join(self.items(), ", ", |item, p| item.pretty(p));
     }
 }
 
@@ -372,15 +393,16 @@ impl Pretty for CallArg {
 
 impl Pretty for ClosureExpr {
     fn pretty(&self, p: &mut Printer) {
-        if let [param] = self.params.as_slice() {
+        let params: Vec<_> = self.params().collect();
+        if let [param] = params.as_slice() {
             param.pretty(p);
         } else {
             p.push('(');
-            p.join(self.params.iter(), ", ", |item, p| item.pretty(p));
+            p.join(params.iter(), ", ", |item, p| item.pretty(p));
             p.push(')');
         }
         p.push_str(" => ");
-        self.body.pretty(p);
+        self.body().pretty(p);
     }
 }
 
@@ -399,9 +421,9 @@ impl Pretty for ClosureParam {
 
 impl Pretty for WithExpr {
     fn pretty(&self, p: &mut Printer) {
-        self.callee.pretty(p);
+        self.callee().pretty(p);
         p.push_str(" with (");
-        self.args.pretty(p);
+        self.args().pretty(p);
         p.push(')');
     }
 }
@@ -409,13 +431,13 @@ impl Pretty for WithExpr {
 impl Pretty for LetExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push_str("let ");
-        self.binding.pretty(p);
-        if let Some(Expr::Closure(closure)) = &self.init {
+        self.binding().pretty(p);
+        if let Some(Expr::Closure(closure)) = self.init() {
             p.push('(');
-            p.join(closure.params.iter(), ", ", |item, p| item.pretty(p));
+            p.join(closure.params(), ", ", |item, p| item.pretty(p));
             p.push_str(") = ");
-            closure.body.pretty(p);
-        } else if let Some(init) = &self.init {
+            closure.body().pretty(p);
+        } else if let Some(init) = self.init() {
             p.push_str(" = ");
             init.pretty(p);
         }
@@ -425,10 +447,10 @@ impl Pretty for LetExpr {
 impl Pretty for IfExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push_str("if ");
-        self.condition.pretty(p);
+        self.condition().pretty(p);
         p.push(' ');
-        self.if_body.pretty(p);
-        if let Some(expr) = &self.else_body {
+        self.if_body().pretty(p);
+        if let Some(expr) = self.else_body() {
             p.push_str(" else ");
             expr.pretty(p);
         }
@@ -438,42 +460,40 @@ impl Pretty for IfExpr {
 impl Pretty for WhileExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push_str("while ");
-        self.condition.pretty(p);
+        self.condition().pretty(p);
         p.push(' ');
-        self.body.pretty(p);
+        self.body().pretty(p);
     }
 }
 
 impl Pretty for ForExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push_str("for ");
-        self.pattern.pretty(p);
+        self.pattern().pretty(p);
         p.push_str(" in ");
-        self.iter.pretty(p);
+        self.iter().pretty(p);
         p.push(' ');
-        self.body.pretty(p);
+        self.body().pretty(p);
     }
 }
 
 impl Pretty for ForPattern {
     fn pretty(&self, p: &mut Printer) {
-        match self {
-            Self::Value(v) => v.pretty(p),
-            Self::KeyValue(k, v) => {
-                k.pretty(p);
-                p.push_str(", ");
-                v.pretty(p);
-            }
+        if let Some(key) = self.key() {
+            key.pretty(p);
+            p.push_str(", ");
         }
+
+        self.value().pretty(p);
     }
 }
 
 impl Pretty for ImportExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push_str("import ");
-        self.imports.pretty(p);
+        self.imports().pretty(p);
         p.push_str(" from ");
-        self.path.pretty(p);
+        self.path().pretty(p);
     }
 }
 
@@ -481,7 +501,9 @@ impl Pretty for Imports {
     fn pretty(&self, p: &mut Printer) {
         match self {
             Self::Wildcard => p.push('*'),
-            Self::Idents(idents) => p.join(idents, ", ", |item, p| item.pretty(p)),
+            Self::Items(idents) => {
+                p.join(idents, ", ", |item, p| item.pretty(p));
+            }
         }
     }
 }
@@ -489,20 +511,19 @@ impl Pretty for Imports {
 impl Pretty for IncludeExpr {
     fn pretty(&self, p: &mut Printer) {
         p.push_str("include ");
-        self.path.pretty(p);
+        self.path().pretty(p);
     }
 }
 
 impl Pretty for Ident {
     fn pretty(&self, p: &mut Printer) {
-        p.push_str(self.as_str());
+        p.push_str(self);
     }
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::parse::parse;
     use crate::source::SourceFile;
 
     #[track_caller]
@@ -513,7 +534,7 @@ mod tests {
     #[track_caller]
     fn test_parse(src: &str, expected: &str) {
         let source = SourceFile::detached(src);
-        let ast = parse(&source).unwrap();
+        let ast = source.ast().unwrap();
         let found = pretty(&ast);
         if found != expected {
             println!("tree:     {:#?}", ast);
@@ -551,6 +572,11 @@ mod tests {
         test_parse("``` 1```", "`1`");
         test_parse("``` 1 ```", "`1 `");
         test_parse("```` ` ````", "``` ` ```");
+
+        // Math node.
+        roundtrip("$$");
+        roundtrip("$a+b$");
+        roundtrip("$[ a^2 + b^2 = c^2 ]$");
     }
 
     #[test]
diff --git a/src/syntax/span.rs b/src/syntax/span.rs
index bfb9e755..47d96589 100644
--- a/src/syntax/span.rs
+++ b/src/syntax/span.rs
@@ -1,6 +1,6 @@
 use std::cmp::Ordering;
 use std::fmt::{self, Debug, Formatter};
-use std::ops::{Add, Range};
+use std::ops::Range;
 
 use serde::{Deserialize, Serialize};
 
@@ -53,23 +53,19 @@ pub struct Span {
     /// The id of the source file.
     pub source: SourceId,
     /// The inclusive start position.
-    pub start: Pos,
+    pub start: usize,
     /// The inclusive end position.
-    pub end: Pos,
+    pub end: usize,
 }
 
 impl Span {
     /// Create a new span from start and end positions.
-    pub fn new(source: SourceId, start: impl Into<Pos>, end: impl Into<Pos>) -> Self {
-        Self {
-            source,
-            start: start.into(),
-            end: end.into(),
-        }
+    pub fn new(source: SourceId, start: usize, end: usize) -> Self {
+        Self { source, start, end }
     }
 
     /// Create a span including just a single position.
-    pub fn at(source: SourceId, pos: impl Into<Pos> + Copy) -> Self {
+    pub fn at(source: SourceId, pos: usize) -> Self {
         Self::new(source, pos, pos)
     }
 
@@ -77,19 +73,34 @@ impl Span {
     pub fn detached() -> Self {
         Self {
             source: SourceId::from_raw(0),
-            start: Pos::ZERO,
-            end: Pos::ZERO,
+            start: 0,
+            end: 0,
         }
     }
 
     /// Create a span with a different start position.
-    pub fn with_start(self, start: impl Into<Pos>) -> Self {
-        Self { start: start.into(), ..self }
+    pub fn with_start(self, start: usize) -> Self {
+        Self { start, ..self }
     }
 
     /// Create a span with a different end position.
-    pub fn with_end(self, end: impl Into<Pos>) -> Self {
-        Self { end: end.into(), ..self }
+    pub fn with_end(self, end: usize) -> Self {
+        Self { end, ..self }
+    }
+
+    /// The byte length of the spanned region.
+    pub fn len(self) -> usize {
+        self.end - self.start
+    }
+
+    /// A new span at the position of this span's start.
+    pub fn at_start(&self) -> Span {
+        Self::at(self.source, self.start)
+    }
+
+    /// A new span at the position of this span's end.
+    pub fn at_end(&self) -> Span {
+        Self::at(self.source, self.end)
     }
 
     /// Create a new span with the earlier start and later end position.
@@ -109,14 +120,19 @@ impl Span {
         *self = self.join(other)
     }
 
+    /// Test whether a position is within the span.
+    pub fn contains(&self, pos: usize) -> bool {
+        self.start <= pos && self.end >= pos
+    }
+
     /// Test whether one span complete contains the other span.
-    pub fn contains(self, other: Self) -> bool {
+    pub fn surrounds(self, other: Self) -> bool {
         self.source == other.source && self.start <= other.start && self.end >= other.end
     }
 
-    /// Convert to a `Range<Pos>` for indexing.
+    /// Convert to a `Range<usize>` for indexing.
     pub fn to_range(self) -> Range<usize> {
-        self.start.to_usize() .. self.end.to_usize()
+        self.start .. self.end
     }
 }
 
@@ -135,77 +151,3 @@ impl PartialOrd for Span {
         }
     }
 }
-
-/// A byte position in source code.
-#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Serialize, Deserialize)]
-pub struct Pos(pub u32);
-
-impl Pos {
-    /// The zero position.
-    pub const ZERO: Self = Self(0);
-
-    /// Convert to a usize for indexing.
-    pub fn to_usize(self) -> usize {
-        self.0 as usize
-    }
-}
-
-impl Debug for Pos {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        Debug::fmt(&self.0, f)
-    }
-}
-
-impl From<u32> for Pos {
-    fn from(index: u32) -> Self {
-        Self(index)
-    }
-}
-
-impl From<usize> for Pos {
-    fn from(index: usize) -> Self {
-        Self(index as u32)
-    }
-}
-
-impl<T> Add<T> for Pos
-where
-    T: Into<Pos>,
-{
-    type Output = Self;
-
-    fn add(self, rhs: T) -> Self {
-        Pos(self.0 + rhs.into().0)
-    }
-}
-
-/// Convert a position or range into a span.
-pub trait IntoSpan {
-    /// Convert into a span by providing the source id.
-    fn into_span(self, source: SourceId) -> Span;
-}
-
-impl IntoSpan for Span {
-    fn into_span(self, source: SourceId) -> Span {
-        debug_assert_eq!(self.source, source);
-        self
-    }
-}
-
-impl IntoSpan for Pos {
-    fn into_span(self, source: SourceId) -> Span {
-        Span::new(source, self, self)
-    }
-}
-
-impl IntoSpan for usize {
-    fn into_span(self, source: SourceId) -> Span {
-        Span::new(source, self, self)
-    }
-}
-
-impl IntoSpan for Range<usize> {
-    fn into_span(self, source: SourceId) -> Span {
-        Span::new(source, self.start, self.end)
-    }
-}
diff --git a/src/syntax/token.rs b/src/syntax/token.rs
deleted file mode 100644
index 22dd104b..00000000
--- a/src/syntax/token.rs
+++ /dev/null
@@ -1,276 +0,0 @@
-use crate::geom::{AngularUnit, LengthUnit};
-
-/// A minimal semantic entity of source code.
-#[derive(Debug, Copy, Clone, PartialEq)]
-pub enum Token<'s> {
-    /// A left square bracket: `[`.
-    LeftBracket,
-    /// A right square bracket: `]`.
-    RightBracket,
-    /// A left curly brace: `{`.
-    LeftBrace,
-    /// A right curly brace: `}`.
-    RightBrace,
-    /// A left round parenthesis: `(`.
-    LeftParen,
-    /// A right round parenthesis: `)`.
-    RightParen,
-    /// An asterisk: `*`.
-    Star,
-    /// An underscore: `_`.
-    Underscore,
-    /// A tilde: `~`.
-    Tilde,
-    /// Two hyphens: `--`.
-    HyphHyph,
-    /// Three hyphens: `---`.
-    HyphHyphHyph,
-    /// A backslash followed by nothing or whitespace: `\`.
-    Backslash,
-    /// A comma: `,`.
-    Comma,
-    /// A semicolon: `;`.
-    Semicolon,
-    /// A colon: `:`.
-    Colon,
-    /// A plus: `+`.
-    Plus,
-    /// A hyphen: `-`.
-    Hyph,
-    /// A slash: `/`.
-    Slash,
-    /// A single equals sign: `=`.
-    Eq,
-    /// Two equals signs: `==`.
-    EqEq,
-    /// An exclamation mark followed by an equals sign: `!=`.
-    ExclEq,
-    /// A less-than sign: `<`.
-    Lt,
-    /// A less-than sign followed by an equals sign: `<=`.
-    LtEq,
-    /// A greater-than sign: `>`.
-    Gt,
-    /// A greater-than sign followed by an equals sign: `>=`.
-    GtEq,
-    /// A plus followed by an equals sign: `+=`.
-    PlusEq,
-    /// A hyphen followed by an equals sign: `-=`.
-    HyphEq,
-    /// An asterisk followed by an equals sign: `*=`.
-    StarEq,
-    /// A slash followed by an equals sign: `/=`.
-    SlashEq,
-    /// Two dots: `..`.
-    Dots,
-    /// An equals sign followed by a greater-than sign: `=>`.
-    Arrow,
-    /// The `not` operator.
-    Not,
-    /// The `and` operator.
-    And,
-    /// The `or` operator.
-    Or,
-    /// The `with` operator.
-    With,
-    /// The none literal: `none`.
-    None,
-    /// The auto literal: `auto`.
-    Auto,
-    /// The `let` keyword.
-    Let,
-    /// The `if` keyword.
-    If,
-    /// The `else` keyword.
-    Else,
-    /// The `for` keyword.
-    For,
-    /// The `in` keyword.
-    In,
-    /// The `while` keyword.
-    While,
-    /// The `break` keyword.
-    Break,
-    /// The `continue` keyword.
-    Continue,
-    /// The `return` keyword.
-    Return,
-    /// The `import` keyword.
-    Import,
-    /// The `include` keyword.
-    Include,
-    /// The `from` keyword.
-    From,
-    /// One or more whitespace characters.
-    ///
-    /// The contained `usize` denotes the number of newlines that were contained
-    /// in the whitespace.
-    Space(usize),
-    /// A consecutive non-markup string.
-    Text(&'s str),
-    /// A slash and the letter "u" followed by a hexadecimal unicode entity
-    /// enclosed in curly braces: `\u{1F5FA}`.
-    UnicodeEscape(UnicodeEscapeToken<'s>),
-    /// An arbitrary number of backticks followed by inner contents, terminated
-    /// with the same number of backticks: `` `...` ``.
-    Raw(RawToken<'s>),
-    /// One or two dollar signs followed by inner contents, terminated with the
-    /// same number of dollar signs.
-    Math(MathToken<'s>),
-    /// A numbering: `23.`.
-    ///
-    /// Can also exist without the number: `.`.
-    Numbering(Option<usize>),
-    /// An identifier: `center`.
-    Ident(&'s str),
-    /// A boolean: `true`, `false`.
-    Bool(bool),
-    /// An integer: `120`.
-    Int(i64),
-    /// A floating-point number: `1.2`, `10e-4`.
-    Float(f64),
-    /// A length: `12pt`, `3cm`.
-    Length(f64, LengthUnit),
-    /// An angle: `90deg`.
-    Angle(f64, AngularUnit),
-    /// A percentage: `50%`.
-    ///
-    /// _Note_: `50%` is stored as `50.0` here, as in the corresponding
-    /// [literal](super::Lit::Percent).
-    Percent(f64),
-    /// A fraction unit: `3fr`.
-    Fraction(f64),
-    /// A quoted string: `"..."`.
-    Str(StrToken<'s>),
-    /// Two slashes followed by inner contents, terminated with a newline:
-    /// `//<str>\n`.
-    LineComment(&'s str),
-    /// A slash and a star followed by inner contents,  terminated with a star
-    /// and a slash: `/*<str>*/`.
-    ///
-    /// The comment can contain nested block comments.
-    BlockComment(&'s str),
-    /// Things that are not valid tokens.
-    Invalid(&'s str),
-}
-
-/// A quoted string token: `"..."`.
-#[derive(Debug, Copy, Clone, PartialEq)]
-pub struct StrToken<'s> {
-    /// The string inside the quotes.
-    ///
-    /// _Note_: If the string contains escape sequences these are not yet
-    /// applied to be able to just store a string slice here instead of
-    /// a `String`. The resolving is done later in the parser.
-    pub string: &'s str,
-    /// Whether the closing quote was present.
-    pub terminated: bool,
-}
-
-/// A raw block token: `` `...` ``.
-#[derive(Debug, Copy, Clone, PartialEq)]
-pub struct RawToken<'s> {
-    /// The raw text between the backticks.
-    pub text: &'s str,
-    /// The number of opening backticks.
-    pub backticks: usize,
-    /// Whether all closing backticks were present.
-    pub terminated: bool,
-}
-
-/// A math formula token: `$2pi + x$` or `$[f'(x) = x^2]$`.
-#[derive(Debug, Copy, Clone, PartialEq)]
-pub struct MathToken<'s> {
-    /// The formula between the dollars.
-    pub formula: &'s str,
-    /// Whether the formula is display-level, that is, it is surrounded by
-    /// `$[..]`.
-    pub display: bool,
-    /// Whether the closing dollars were present.
-    pub terminated: bool,
-}
-
-/// A unicode escape sequence token: `\u{1F5FA}`.
-#[derive(Debug, Copy, Clone, PartialEq)]
-pub struct UnicodeEscapeToken<'s> {
-    /// The escape sequence between the braces.
-    pub sequence: &'s str,
-    /// Whether the closing brace was present.
-    pub terminated: bool,
-}
-
-impl<'s> Token<'s> {
-    /// The English name of this token for use in error messages.
-    pub fn name(self) -> &'static str {
-        match self {
-            Self::LeftBracket => "opening bracket",
-            Self::RightBracket => "closing bracket",
-            Self::LeftBrace => "opening brace",
-            Self::RightBrace => "closing brace",
-            Self::LeftParen => "opening paren",
-            Self::RightParen => "closing paren",
-            Self::Star => "star",
-            Self::Underscore => "underscore",
-            Self::Tilde => "tilde",
-            Self::HyphHyph => "en dash",
-            Self::HyphHyphHyph => "em dash",
-            Self::Backslash => "backslash",
-            Self::Comma => "comma",
-            Self::Semicolon => "semicolon",
-            Self::Colon => "colon",
-            Self::Plus => "plus",
-            Self::Hyph => "minus",
-            Self::Slash => "slash",
-            Self::Eq => "assignment operator",
-            Self::EqEq => "equality operator",
-            Self::ExclEq => "inequality operator",
-            Self::Lt => "less-than operator",
-            Self::LtEq => "less-than or equal operator",
-            Self::Gt => "greater-than operator",
-            Self::GtEq => "greater-than or equal operator",
-            Self::PlusEq => "add-assign operator",
-            Self::HyphEq => "subtract-assign operator",
-            Self::StarEq => "multiply-assign operator",
-            Self::SlashEq => "divide-assign operator",
-            Self::Dots => "dots",
-            Self::Arrow => "arrow",
-            Self::Not => "operator `not`",
-            Self::And => "operator `and`",
-            Self::Or => "operator `or`",
-            Self::With => "operator `with`",
-            Self::None => "`none`",
-            Self::Auto => "`auto`",
-            Self::Let => "keyword `let`",
-            Self::If => "keyword `if`",
-            Self::Else => "keyword `else`",
-            Self::For => "keyword `for`",
-            Self::In => "keyword `in`",
-            Self::While => "keyword `while`",
-            Self::Break => "keyword `break`",
-            Self::Continue => "keyword `continue`",
-            Self::Return => "keyword `return`",
-            Self::Import => "keyword `import`",
-            Self::Include => "keyword `include`",
-            Self::From => "keyword `from`",
-            Self::Space(_) => "space",
-            Self::Text(_) => "text",
-            Self::UnicodeEscape(_) => "unicode escape sequence",
-            Self::Raw(_) => "raw block",
-            Self::Math(_) => "math formula",
-            Self::Numbering(_) => "numbering",
-            Self::Ident(_) => "identifier",
-            Self::Bool(_) => "boolean",
-            Self::Int(_) => "integer",
-            Self::Float(_) => "float",
-            Self::Length(_, _) => "length",
-            Self::Angle(_, _) => "angle",
-            Self::Percent(_) => "percentage",
-            Self::Fraction(_) => "`fr` value",
-            Self::Str(_) => "string",
-            Self::LineComment(_) => "line comment",
-            Self::BlockComment(_) => "block comment",
-            Self::Invalid("*/") => "end of block comment",
-            Self::Invalid(_) => "invalid token",
-        }
-    }
-}
diff --git a/src/syntax/visit.rs b/src/syntax/visit.rs
deleted file mode 100644
index 40e8eb93..00000000
--- a/src/syntax/visit.rs
+++ /dev/null
@@ -1,263 +0,0 @@
-//! Mutable and immutable syntax tree traversal.
-
-use super::*;
-
-/// Implement the immutable and the mutable visitor version.
-macro_rules! impl_visitors {
-    ($($name:ident($($tts:tt)*) $body:block)*) => {
-        macro_rules! r {
-            (rc: $x:expr) => { $x.as_ref() };
-            ($x:expr) => { &$x };
-        }
-
-        impl_visitor! {
-            Visit,
-            immutable,
-            immutably,
-            [$(($name($($tts)*) $body))*]
-        }
-
-        macro_rules! r {
-            (rc: $x:expr) => { std::rc::Rc::make_mut(&mut $x) };
-            ($x:expr) => { &mut $x };
-        }
-
-        impl_visitor! {
-            VisitMut,
-            mutable,
-            mutably,
-            [$(($name($($tts)*) $body mut))*] mut
-        }
-    };
-}
-
-/// Implement an immutable or mutable visitor.
-macro_rules! impl_visitor {
-    (
-        $visit:ident,
-        $mutability:ident,
-        $adjective:ident,
-        [$((
-            $name:ident($v:ident, $node:ident: $ty:ty)
-            $body:block
-            $($fmut:tt)?
-        ))*]
-        $($mut:tt)?
-    ) => {
-        #[doc = concat!("Visit syntax trees ", stringify!($adjective), ".")]
-        pub trait $visit<'ast> {
-            /// Visit a definition of a binding.
-            ///
-            /// Bindings are, for example, left-hand side of let expressions,
-            /// and key/value patterns in for loops.
-            fn visit_binding(&mut self, _: &'ast $($mut)? Ident) {}
-
-            /// Visit the entry into a scope.
-            fn visit_enter(&mut self) {}
-
-            /// Visit the exit from a scope.
-            fn visit_exit(&mut self) {}
-
-            $(fn $name(&mut self, $node: &'ast $($fmut)? $ty) {
-                $mutability::$name(self, $node);
-            })*
-        }
-
-        #[doc = concat!("Visitor functions that are ", stringify!($mutability), ".")]
-        pub mod $mutability {
-            use super::*;
-            $(
-                #[doc = concat!("Visit a node of type [`", stringify!($ty), "`].")]
-                pub fn $name<'ast, V>($v: &mut V, $node: &'ast $($fmut)? $ty)
-                where
-                    V: $visit<'ast> + ?Sized
-                $body
-            )*
-        }
-    };
-}
-
-impl_visitors! {
-    visit_tree(v, markup: Markup) {
-        for node in markup {
-            v.visit_node(node);
-        }
-    }
-
-    visit_node(v, node: MarkupNode) {
-        match node {
-            MarkupNode::Space => {}
-            MarkupNode::Linebreak(_) => {}
-            MarkupNode::Parbreak(_) => {}
-            MarkupNode::Strong(_) => {}
-            MarkupNode::Emph(_) => {}
-            MarkupNode::Text(_) => {}
-            MarkupNode::Raw(_) => {}
-            MarkupNode::Heading(n) => v.visit_heading(n),
-            MarkupNode::List(n) => v.visit_list(n),
-            MarkupNode::Enum(n) => v.visit_enum(n),
-            MarkupNode::Expr(n) => v.visit_expr(n),
-        }
-    }
-
-    visit_heading(v, heading: HeadingNode) {
-        v.visit_tree(r!(heading.body));
-    }
-
-    visit_list(v, list: ListNode) {
-        v.visit_tree(r!(list.body));
-    }
-
-    visit_enum(v, enum_: EnumNode) {
-        v.visit_tree(r!(enum_.body));
-    }
-
-    visit_expr(v, expr: Expr) {
-        match expr {
-            Expr::Ident(_) => {}
-            Expr::Lit(_) => {},
-            Expr::Array(e) => v.visit_array(e),
-            Expr::Dict(e) => v.visit_dict(e),
-            Expr::Template(e) => v.visit_template(e),
-            Expr::Group(e) => v.visit_group(e),
-            Expr::Block(e) => v.visit_block(e),
-            Expr::Unary(e) => v.visit_unary(e),
-            Expr::Binary(e) => v.visit_binary(e),
-            Expr::Call(e) => v.visit_call(e),
-            Expr::Closure(e) => v.visit_closure(e),
-            Expr::With(e) => v.visit_with(e),
-            Expr::Let(e) => v.visit_let(e),
-            Expr::If(e) => v.visit_if(e),
-            Expr::While(e) => v.visit_while(e),
-            Expr::For(e) => v.visit_for(e),
-            Expr::Import(e) => v.visit_import(e),
-            Expr::Include(e) => v.visit_include(e),
-        }
-    }
-
-    visit_array(v, array: ArrayExpr) {
-        for expr in r!(array.items) {
-            v.visit_expr(expr);
-        }
-    }
-
-    visit_dict(v, dict: DictExpr) {
-        for named in r!(dict.items) {
-            v.visit_expr(r!(named.expr));
-        }
-    }
-
-    visit_template(v, template: TemplateExpr) {
-        v.visit_enter();
-        v.visit_tree(r!(template.body));
-        v.visit_exit();
-    }
-
-    visit_group(v, group: GroupExpr) {
-        v.visit_expr(r!(group.expr));
-    }
-
-    visit_block(v, block: BlockExpr) {
-        v.visit_enter();
-        for expr in r!(block.exprs) {
-            v.visit_expr(expr);
-        }
-        v.visit_exit();
-    }
-
-    visit_binary(v, binary: BinaryExpr) {
-        v.visit_expr(r!(binary.lhs));
-        v.visit_expr(r!(binary.rhs));
-    }
-
-    visit_unary(v, unary: UnaryExpr) {
-        v.visit_expr(r!(unary.expr));
-    }
-
-    visit_call(v, call: CallExpr) {
-        v.visit_expr(r!(call.callee));
-        v.visit_args(r!(call.args));
-    }
-
-    visit_args(v, args: CallArgs) {
-        for arg in r!(args.items) {
-            v.visit_arg(arg);
-        }
-    }
-
-    visit_arg(v, arg: CallArg) {
-        match arg {
-            CallArg::Pos(expr) => v.visit_expr(expr),
-            CallArg::Named(named) => v.visit_expr(r!(named.expr)),
-            CallArg::Spread(expr) => v.visit_expr(expr),
-        }
-    }
-
-    visit_closure(v, closure: ClosureExpr) {
-        for param in r!(closure.params) {
-            v.visit_param(param);
-        }
-        v.visit_expr(r!(rc: closure.body));
-    }
-
-    visit_param(v, param: ClosureParam) {
-        match param {
-            ClosureParam::Pos(binding) => v.visit_binding(binding),
-            ClosureParam::Named(named) => {
-                v.visit_binding(r!(named.name));
-                v.visit_expr(r!(named.expr));
-            }
-            ClosureParam::Sink(binding) => v.visit_binding(binding),
-        }
-    }
-
-    visit_with(v, with_expr: WithExpr) {
-        v.visit_expr(r!(with_expr.callee));
-        v.visit_args(r!(with_expr.args));
-    }
-
-    visit_let(v, let_expr: LetExpr) {
-        if let Some(init) = r!(let_expr.init) {
-            v.visit_expr(init);
-        }
-        v.visit_binding(r!(let_expr.binding));
-    }
-
-    visit_if(v, if_expr: IfExpr) {
-        v.visit_expr(r!(if_expr.condition));
-        v.visit_expr(r!(if_expr.if_body));
-        if let Some(body) = r!(if_expr.else_body) {
-            v.visit_expr(body);
-        }
-    }
-
-    visit_while(v, while_expr: WhileExpr) {
-        v.visit_expr(r!(while_expr.condition));
-        v.visit_expr(r!(while_expr.body));
-    }
-
-    visit_for(v, for_expr: ForExpr) {
-        v.visit_expr(r!(for_expr.iter));
-        match r!(for_expr.pattern) {
-            ForPattern::Value(value) => v.visit_binding(value),
-            ForPattern::KeyValue(key, value) => {
-                v.visit_binding(key);
-                v.visit_binding(value);
-            }
-        }
-        v.visit_expr(r!(for_expr.body));
-    }
-
-    visit_import(v, import_expr: ImportExpr) {
-        v.visit_expr(r!(import_expr.path));
-        if let Imports::Idents(idents) = r!(import_expr.imports) {
-            for ident in idents {
-                v.visit_binding(ident);
-            }
-        }
-    }
-
-    visit_include(v, include_expr: IncludeExpr) {
-        v.visit_expr(r!(include_expr.path));
-    }
-}
diff --git a/tests/ref/markup/heading.png b/tests/ref/markup/heading.png
index ca52644b..c33da420 100644
--- a/tests/ref/markup/heading.png
+++ b/tests/ref/markup/heading.png
diff --git a/tests/ref/markup/math.png b/tests/ref/markup/math.png
new file mode 100644
index 00000000..426f3dbf
--- /dev/null
+++ b/tests/ref/markup/math.png
diff --git a/tests/typ/code/closure.typ b/tests/typ/code/closure.typ
index 3b8b4261..14e74e7e 100644
--- a/tests/typ/code/closure.typ
+++ b/tests/typ/code/closure.typ
@@ -57,6 +57,52 @@
 }
 
 ---
+// Import bindings.
+{
+  let b = "target.typ"
+  let f() = {
+    import b from b
+    b
+  }
+  test(f(), 1)
+}
+
+---
+// For loop bindings.
+{
+  let v = (1, 2, 3)
+  let s = 0
+  let f() = {
+    for v in v { s += v }
+  }
+  f()
+  test(s, 6)
+}
+
+---
+// Let + closure bindings.
+{
+  let g = "hi"
+  let f() = {
+    let g() = "bye"
+    g()
+  }
+  test(f(), "bye")
+}
+
+---
+// Parameter bindings.
+{
+  let x = 5
+  let g() = {
+    let f(x, y: x) = x + y
+    f
+  }
+
+  test(g()(8), 13)
+}
+
+---
 // Don't leak environment.
 {
   // Error: 16-17 unknown variable
diff --git a/tests/typ/code/import.typ b/tests/typ/code/import.typ
index bc96e80c..683bb52a 100644
--- a/tests/typ/code/import.typ
+++ b/tests/typ/code/import.typ
@@ -79,7 +79,7 @@ This is never reached.
 // Error: 22 expected keyword `from`
 #import afrom, "b", c
 
-// Error: 8 expected import items
+// Error: 9 expected import items
 #import from "target.typ"
 
 // Error: 9-10 expected expression, found assignment operator
diff --git a/tests/typ/code/let.typ b/tests/typ/code/let.typ
index 3f3f9d35..cd7531b7 100644
--- a/tests/typ/code/let.typ
+++ b/tests/typ/code/let.typ
@@ -56,7 +56,7 @@ Three
 #let v4 = 4 Four
 
 // Terminated by semicolon even though we are in a paren group.
-// Error: 19 expected expression
+// Error: 18 expected expression
 // Error: 19 expected closing paren
 #let v5 = (1, 2 + ; Five
 
diff --git a/tests/typ/code/spread.typ b/tests/typ/code/spread.typ
index 8a9491d0..41e790a4 100644
--- a/tests/typ/code/spread.typ
+++ b/tests/typ/code/spread.typ
@@ -62,7 +62,7 @@
 #min(.."nope")
 
 ---
-// Error: 10-14 expected identifier
+// Error: 8-14 expected identifier
 #let f(..true) = none
 
 ---
@@ -70,9 +70,9 @@
 #let f(..a, ..b) = none
 
 ---
-// Error: 5-6 spreading is not allowed here
+// Error: 3-6 spreading is not allowed here
 {(..x)}
 
 ---
-// Error: 11-17 spreading is not allowed here
+// Error: 9-17 spreading is not allowed here
 {(1, 2, ..(1, 2))}
diff --git a/tests/typ/markup/heading.typ b/tests/typ/markup/heading.typ
index 4647e7a6..cb022617 100644
--- a/tests/typ/markup/heading.typ
+++ b/tests/typ/markup/heading.typ
@@ -8,8 +8,8 @@
 === Level 2
 ====== Level 6
 
-// Too many hashtags.
-======= Level 7
+// At some point, it should stop shrinking.
+=========== Level 11
 
 ---
 // Heading vs. no heading.
diff --git a/tests/typ/markup/math.typ b/tests/typ/markup/math.typ
new file mode 100644
index 00000000..cad01d10
--- /dev/null
+++ b/tests/typ/markup/math.typ
@@ -0,0 +1,12 @@
+// Test math formulas.
+
+---
+The sum of $a$ and $b$ is $a + b$.
+
+---
+We will show that:
+$[ a^2 + b^2 = c^2 ]$
+
+---
+// Error: 2:1 expected closing bracket and dollar sign
+$[a
diff --git a/tests/typ/markup/raw.typ b/tests/typ/markup/raw.typ
index d48432f7..0e053a9b 100644
--- a/tests/typ/markup/raw.typ
+++ b/tests/typ/markup/raw.typ
@@ -55,5 +55,5 @@ The keyword ```rust let```.
 
 ---
 // Unterminated.
-// Error: 2:1 expected backtick(s)
+// Error: 2:1 expected 1 backtick
 `endless
diff --git a/tests/typeset.rs b/tests/typeset.rs
index bde383c4..68e56343 100644
--- a/tests/typeset.rs
+++ b/tests/typeset.rs
@@ -24,7 +24,7 @@ use typst::loading::FsLoader;
 use typst::parse::Scanner;
 use typst::source::SourceFile;
 use typst::style::Style;
-use typst::syntax::{Pos, Span};
+use typst::syntax::Span;
 use typst::Context;
 
 const TYP_DIR: &str = "./typ";
@@ -355,12 +355,12 @@ fn parse_metadata(source: &SourceFile) -> (Option<bool>, Vec<Error>) {
         let comments =
             lines[i ..].iter().take_while(|line| line.starts_with("//")).count();
 
-        let pos = |s: &mut Scanner| -> Pos {
+        let pos = |s: &mut Scanner| -> usize {
             let first = num(s) - 1;
             let (delta, column) =
                 if s.eat_if(':') { (first, num(s) - 1) } else { (0, first) };
             let line = (i + comments) + delta;
-            source.line_column_to_byte(line, column).unwrap().into()
+            source.line_column_to_byte(line, column).unwrap()
         };
 
         let mut s = Scanner::new(rest);
@@ -375,10 +375,10 @@ fn parse_metadata(source: &SourceFile) -> (Option<bool>, Vec<Error>) {
 }
 
 fn print_error(source: &SourceFile, line: usize, error: &Error) {
-    let start_line = 1 + line + source.byte_to_line(error.span.start.to_usize()).unwrap();
-    let start_col = 1 + source.byte_to_column(error.span.start.to_usize()).unwrap();
-    let end_line = 1 + line + source.byte_to_line(error.span.end.to_usize()).unwrap();
-    let end_col = 1 + source.byte_to_column(error.span.end.to_usize()).unwrap();
+    let start_line = 1 + line + source.byte_to_line(error.span.start).unwrap();
+    let start_col = 1 + source.byte_to_column(error.span.start).unwrap();
+    let end_line = 1 + line + source.byte_to_line(error.span.end).unwrap();
+    let end_col = 1 + source.byte_to_column(error.span.end).unwrap();
     println!(
         "Error: {}:{}-{}:{}: {}",
         start_line, start_col, end_line, end_col, error.message