diff --git a/Cargo.toml b/Cargo.toml
index 2082d9163..b2c385d41 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,9 +9,9 @@ build = "build.rs"
 toddle = { path = "../toddle", default-features = false }
 tide = { path = "../tide" }
 byteorder = "1"
-smallvec = "0.6.10"
-unicode-xid = "0.1.0"
-async-trait = "0.1.22"
+smallvec = "1"
+unicode-xid = "0.2"
+async-trait = "0.1"
 futures-executor = { version = "0.3", optional = true }
 
 [features]
diff --git a/src/func/macros.rs b/src/func/macros.rs
index 9e931ea2c..1083e53c6 100644
--- a/src/func/macros.rs
+++ b/src/func/macros.rs
@@ -75,6 +75,8 @@ macro_rules! function {
         parse($args:ident, $body:pat, $ctx:pat, $metadata:pat) $code:block
         $($rest:tt)*
     ) => {
+        use $crate::func::prelude::*;
+
         impl $crate::func::ParseFunc for $type {
             type Meta = $meta;
 
@@ -88,7 +90,8 @@ macro_rules! function {
                 let mut $args = args;
                 let val = $code;
                 if !$args.is_empty() {
-                    error!(unexpected_argument);
+                    return Err($crate::TypesetError
+                        ::with_message("unexpected arguments"));
                 }
                 Ok(val)
             }
@@ -109,6 +112,8 @@ macro_rules! function {
 
     // (2-arg) Parse a layout-definition with all arguments.
     (@layout $type:ident | layout($this:ident, $ctx:pat) $code:block) => {
+        use $crate::func::prelude::*;
+
         impl LayoutFunc for $type {
             fn layout<'a, 'life0, 'life1, 'async_trait>(
                 &'a $this,
@@ -138,13 +143,13 @@ macro_rules! function {
 macro_rules! parse {
     (forbidden: $body:expr) => {
         if $body.is_some() {
-            error!("unexpected body");
+            return Err($crate::TypesetError::with_message("unexpected body"));
         }
     };
 
     (optional: $body:expr, $ctx:expr) => (
         if let Some(body) = $body {
-            Some($crate::syntax::parse(body, $ctx))
+            Some($crate::syntax::parse(body, $ctx).0)
         } else {
             None
         }
@@ -152,9 +157,9 @@ macro_rules! parse {
 
     (expected: $body:expr, $ctx:expr) => (
         if let Some(body) = $body {
-            $crate::syntax::parse(body, $ctx)?
+            $crate::syntax::parse(body, $ctx).0
         } else {
-            error!("expected body");
+            Err($crate::TypesetError::with_message("unexpected body"))
         }
     )
 }
diff --git a/src/func/mod.rs b/src/func/mod.rs
index 5f4918d92..90b2a31d3 100644
--- a/src/func/mod.rs
+++ b/src/func/mod.rs
@@ -119,6 +119,7 @@ pub enum Command<'a> {
 /// A map from identifiers to function parsers.
 pub struct Scope {
     parsers: HashMap<String, Box<Parser>>,
+    debug: Option<Box<Parser>>
 }
 
 /// A function which parses the source of a function into a function type which
@@ -129,11 +130,30 @@ type Parser = dyn Fn(
     ParseContext
 ) -> ParseResult<Box<dyn LayoutFunc>>;
 
+fn make_parser<F>(metadata: <F as ParseFunc>::Meta) -> Box<Parser>
+where F: ParseFunc + LayoutFunc + 'static {
+    Box::new(move |a, b, c| {
+        F::parse(a, b, c, metadata.clone())
+            .map(|f| Box::new(f) as Box<dyn LayoutFunc>)
+    })
+}
+
 impl Scope {
     /// Create a new empty scope.
     pub fn new() -> Scope {
         Scope {
             parsers: HashMap::new(),
+            debug: None,
+        }
+    }
+
+    /// Create a new scope with a debug parser that is invoked if not other
+    /// match is found.
+    pub fn with_debug<F>() -> Scope
+    where F: ParseFunc<Meta=()> + LayoutFunc + 'static {
+        Scope {
+            parsers: HashMap::new(),
+            debug: Some(make_parser::<F>(())),
         }
     }
 
@@ -154,16 +174,14 @@ impl Scope {
     where F: ParseFunc + LayoutFunc + 'static {
         self.parsers.insert(
             name.to_owned(),
-            Box::new(move |a, b, c| {
-                F::parse(a, b, c, metadata.clone())
-                    .map(|f| Box::new(f) as Box<dyn LayoutFunc>)
-            })
+            make_parser::<F>(metadata),
         );
     }
 
     /// Return the parser with the given name if there is one.
     pub(crate) fn get_parser(&self, name: &str) -> Option<&Parser> {
         self.parsers.get(name).map(|x| &**x)
+            .or(self.debug.as_ref().map(|x| &**x))
     }
 }
 
diff --git a/src/lib.rs b/src/lib.rs
index 5756cc21d..17188145e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -28,7 +28,7 @@ use toddle::Error as FontError;
 
 use crate::func::Scope;
 use crate::layout::{MultiLayout, LayoutResult};
-use crate::syntax::{parse, SyntaxTree, ParseContext, Span, ParseResult};
+use crate::syntax::{parse, SyntaxTree, Colorization, ErrorMap, ParseContext, Span};
 use crate::style::{LayoutStyle, PageStyle, TextStyle};
 
 #[macro_use]
@@ -84,7 +84,7 @@ impl<'p> Typesetter<'p> {
     }
 
     /// Parse source code into a syntax tree.
-    pub fn parse(&self, src: &str) -> SyntaxTree {
+    pub fn parse(&self, src: &str) -> (SyntaxTree, Colorization, ErrorMap) {
         let scope = Scope::with_std();
         parse(src, ParseContext { scope: &scope })
     }
@@ -115,7 +115,7 @@ impl<'p> Typesetter<'p> {
 
     /// Process source code directly into a layout.
     pub async fn typeset(&self, src: &str) -> TypesetResult<MultiLayout> {
-        let tree = self.parse(src);
+        let tree = self.parse(src).0;
         let layout = self.layout(&tree).await?;
         Ok(layout)
     }
@@ -132,8 +132,8 @@ pub struct TypesetError {
 
 impl TypesetError {
     /// Create a new typesetting error.
-    pub fn with_message(message: String) -> TypesetError {
-        TypesetError { message, span: None }
+    pub fn with_message(message: impl Into<String>) -> TypesetError {
+        TypesetError { message: message.into(), span: None }
     }
 }
 
diff --git a/src/syntax/color.rs b/src/syntax/color.rs
index 7f34fad71..65525480c 100644
--- a/src/syntax/color.rs
+++ b/src/syntax/color.rs
@@ -1,28 +1,3 @@
-/// Entities which can be colored by syntax highlighting.
-#[derive(Debug, Copy, Clone, Eq, PartialEq)]
-pub enum ColorToken {
-    Comment,
+use super::*;
 
-    Bracket,
-    FuncName,
-    Colon,
 
-    Key,
-    Equals,
-    Comma,
-
-    Paren,
-    Brace,
-
-    ExprIdent,
-    ExprStr,
-    ExprNumber,
-    ExprSize,
-    ExprBool,
-
-    Bold,
-    Italic,
-    Monospace,
-
-    Invalid,
-}
diff --git a/src/syntax/expr.rs b/src/syntax/expr.rs
index e2df3c4e6..b06b29c80 100644
--- a/src/syntax/expr.rs
+++ b/src/syntax/expr.rs
@@ -91,12 +91,6 @@ pub struct Object {
     pub pairs: Vec<Pair>,
 }
 
-#[derive(Clone, PartialEq)]
-pub struct Pair {
-    pub key: Spanned<Ident>,
-    pub value: Spanned<Expression>,
-}
-
 impl Object {
     pub fn new() -> Object {
         Object { pairs: vec![] }
@@ -120,7 +114,7 @@ impl Display for Object {
             if !first {
                 write!(f, ", ")?;
             }
-            write!(f, "{}: {}", pair.key.v, pair.value.v)?;
+            write!(f, "{}", pair)?;
             first = false;
         }
 
@@ -128,10 +122,23 @@ impl Display for Object {
     }
 }
 
+#[derive(Clone, PartialEq)]
+pub struct Pair {
+    pub key: Spanned<Ident>,
+    pub value: Spanned<Expression>,
+}
+
+impl Display for Pair {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "{}: {}", self.key.v, self.value.v)
+    }
+}
+
 debug_display!(Ident);
 debug_display!(Expression);
 debug_display!(Tuple);
 debug_display!(Object);
+debug_display!(Pair);
 
 
 /// Kinds of expressions.
diff --git a/src/syntax/mod.rs b/src/syntax/mod.rs
index 11b35a067..1c72de4de 100644
--- a/src/syntax/mod.rs
+++ b/src/syntax/mod.rs
@@ -14,3 +14,247 @@ pub_use_mod!(expr);
 pub_use_mod!(tokens);
 pub_use_mod!(parsing);
 pub_use_mod!(span);
+
+
+/// A minimal semantic entity of source code.
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub enum Token<'s> {
+    /// One or more whitespace characters. The contained `usize` denotes the
+    /// number of newlines that were contained in the whitespace.
+    Whitespace(usize),
+
+    /// A line comment with inner string contents `//<&'s str>\n`.
+    LineComment(&'s str),
+    /// A block comment with inner string contents `/*<&'s str>*/`. The comment
+    /// can contain nested block comments.
+    BlockComment(&'s str),
+    /// An erroneous `*/` without an opening block comment.
+    StarSlash,
+
+    /// A left bracket: `[`.
+    LeftBracket,
+    /// A right bracket: `]`.
+    RightBracket,
+
+    /// A left parenthesis in a function header: `(`.
+    LeftParen,
+    /// A right parenthesis in a function header: `)`.
+    RightParen,
+    /// A left brace in a function header: `{`.
+    LeftBrace,
+    /// A right brace in a function header: `}`.
+    RightBrace,
+
+    /// A colon in a function header: `:`.
+    Colon,
+    /// A comma in a function header: `:`.
+    Comma,
+    /// An equals sign in a function header: `=`.
+    Equals,
+
+    /// An identifier in a function header: `center`.
+    ExprIdent(&'s str),
+    /// A quoted string in a function header: `"..."`.
+    ExprStr(&'s str),
+    /// A number in a function header: `3.14`.
+    ExprNumber(f64),
+    /// A size in a function header: `12pt`.
+    ExprSize(Size),
+    /// A boolean in a function header: `true | false`.
+    ExprBool(bool),
+
+    /// A star in body-text.
+    Star,
+    /// An underscore in body-text.
+    Underscore,
+    /// A backtick in body-text.
+    Backtick,
+
+    /// Any other consecutive string.
+    Text(&'s str),
+}
+
+/// A tree representation of source code.
+#[derive(Debug, PartialEq)]
+pub struct SyntaxTree {
+    pub nodes: Vec<Spanned<Node>>,
+}
+
+impl SyntaxTree {
+    /// Create an empty syntax tree.
+    pub fn new() -> SyntaxTree {
+        SyntaxTree { nodes: vec![] }
+    }
+
+    /// Add a node to the tree.
+    pub fn add(&mut self, node: Spanned<Node>) {
+        self.nodes.push(node);
+    }
+}
+
+/// A node in the syntax tree.
+#[derive(Debug, PartialEq)]
+pub enum Node {
+    /// A number of whitespace characters containing less than two newlines.
+    Space,
+    /// Whitespace characters with more than two newlines.
+    Newline,
+    /// Plain text.
+    Text(String),
+    /// Italics enabled / disabled.
+    ToggleItalic,
+    /// Bolder enabled / disabled.
+    ToggleBolder,
+    /// Monospace enabled / disabled.
+    ToggleMonospace,
+    /// A function invocation.
+    Func(FuncCall),
+}
+
+/// An invocation of a function.
+#[derive(Debug)]
+pub struct FuncCall(pub Box<dyn LayoutFunc>);
+
+impl PartialEq for FuncCall {
+    fn eq(&self, other: &FuncCall) -> bool {
+        &self.0 == &other.0
+    }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct Colorization {
+    pub colors: Vec<Spanned<ColorToken>>,
+}
+
+/// Entities which can be colored by syntax highlighting.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum ColorToken {
+    Comment,
+
+    Bracket,
+    FuncName,
+    Colon,
+
+    Key,
+    Equals,
+    Comma,
+
+    Paren,
+    Brace,
+
+    ExprIdent,
+    ExprStr,
+    ExprNumber,
+    ExprSize,
+    ExprBool,
+
+    Bold,
+    Italic,
+    Monospace,
+
+    Invalid,
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct ErrorMap {
+    pub errors: Vec<Spanned<String>>,
+}
+
+#[derive(Debug)]
+pub struct FuncHeader {
+    pub name: Spanned<Ident>,
+    pub args: FuncArgs,
+}
+
+#[derive(Debug)]
+pub struct FuncArgs {
+    positional: Tuple,
+    keyword: Object,
+}
+
+impl FuncArgs {
+    fn new() -> FuncArgs {
+        FuncArgs {
+            positional: Tuple::new(),
+            keyword: Object::new(),
+        }
+    }
+
+    /// Add a positional argument.
+    pub fn add_pos(&mut self, item: Spanned<Expression>) {
+        self.positional.add(item);
+    }
+
+    /// Force-extract the first positional argument.
+    pub fn get_pos<E: ExpressionKind>(&mut self) -> ParseResult<E> {
+        expect(self.get_pos_opt())
+    }
+
+    /// Extract the first positional argument.
+    pub fn get_pos_opt<E: ExpressionKind>(&mut self) -> ParseResult<Option<E>> {
+        Ok(if !self.positional.items.is_empty() {
+            let spanned = self.positional.items.remove(0);
+            Some(E::from_expr(spanned)?)
+        } else {
+            None
+        })
+    }
+
+    /// Add a keyword argument.
+    pub fn add_key(&mut self, key: Spanned<Ident>, value: Spanned<Expression>) {
+        self.keyword.add(key, value);
+    }
+
+    /// Add a keyword argument from an existing pair.
+    pub fn add_key_pair(&mut self, pair: Pair) {
+        self.keyword.add_pair(pair);
+    }
+
+    /// Force-extract a keyword argument.
+    pub fn get_key<E: ExpressionKind>(&mut self, name: &str) -> ParseResult<E> {
+        expect(self.get_key_opt(name))
+    }
+
+    /// Extract a keyword argument.
+    pub fn get_key_opt<E: ExpressionKind>(&mut self, name: &str) -> ParseResult<Option<E>> {
+        self.keyword.pairs.iter()
+            .position(|p| p.key.v.0 == name)
+            .map(|index| {
+                let value = self.keyword.pairs.swap_remove(index).value;
+                E::from_expr(value)
+            })
+            .transpose()
+    }
+
+    /// Iterator over positional arguments.
+    pub fn iter_pos(&mut self) -> std::vec::IntoIter<Spanned<Expression>> {
+        let tuple = std::mem::replace(&mut self.positional, Tuple::new());
+        tuple.items.into_iter()
+    }
+
+    /// Iterator over all keyword arguments.
+    pub fn iter_keys(&mut self) -> std::vec::IntoIter<Pair> {
+        let object = std::mem::replace(&mut self.keyword, Object::new());
+        object.pairs.into_iter()
+    }
+
+    /// Clear the argument lists.
+    pub fn clear(&mut self) {
+        self.positional.items.clear();
+        self.keyword.pairs.clear();
+    }
+
+    /// Whether both the positional and keyword argument lists are empty.
+    pub fn is_empty(&self) -> bool {
+        self.positional.items.is_empty() && self.keyword.pairs.is_empty()
+    }
+}
+
+/// Extract the option expression kind from the option or return an error.
+fn expect<E: ExpressionKind>(opt: ParseResult<Option<E>>) -> ParseResult<E> {
+    match opt {
+        Ok(Some(spanned)) => Ok(spanned),
+        Ok(None) => error!("expected {}", E::NAME),
+        Err(e) => Err(e),
+    }
+}
diff --git a/src/syntax/parsing.rs b/src/syntax/parsing.rs
index 47322485c..bf3bea893 100644
--- a/src/syntax/parsing.rs
+++ b/src/syntax/parsing.rs
@@ -1,147 +1,10 @@
-use std::iter::Peekable;
-
 use crate::func::Scope;
 use super::*;
 use Token::*;
 
 
-/// A tree representation of source code.
-#[derive(Debug, PartialEq)]
-pub struct SyntaxTree {
-    pub nodes: Vec<Spanned<Node>>,
-}
-
-impl SyntaxTree {
-    /// Create an empty syntax tree.
-    pub fn new() -> SyntaxTree {
-        SyntaxTree { nodes: vec![] }
-    }
-}
-
-/// A node in the syntax tree.
-#[derive(Debug, PartialEq)]
-pub enum Node {
-    /// A number of whitespace characters containing less than two newlines.
-    Space,
-    /// Whitespace characters with more than two newlines.
-    Newline,
-    /// Plain text.
-    Text(String),
-    /// Italics enabled / disabled.
-    ToggleItalic,
-    /// Bolder enabled / disabled.
-    ToggleBolder,
-    /// Monospace enabled / disabled.
-    ToggleMonospace,
-    /// A function invocation.
-    Func(FuncCall),
-}
-
-/// An invocation of a function.
-#[derive(Debug)]
-pub struct FuncCall(pub Box<dyn LayoutFunc>);
-
-impl PartialEq for FuncCall {
-    fn eq(&self, other: &FuncCall) -> bool {
-        &self.0 == &other.0
-    }
-}
-
-#[derive(Debug)]
-pub struct FuncArgs {
-    positional: Tuple,
-    keyword: Object,
-}
-
-impl FuncArgs {
-    fn new() -> FuncArgs {
-        FuncArgs {
-            positional: Tuple::new(),
-            keyword: Object::new(),
-        }
-    }
-
-    /// Add a positional argument.
-    pub fn add_pos(&mut self, item: Spanned<Expression>) {
-        self.positional.add(item);
-    }
-
-    /// Force-extract the first positional argument.
-    pub fn get_pos<E: ExpressionKind>(&mut self) -> ParseResult<E> {
-        expect(self.get_pos_opt())
-    }
-
-    /// Extract the first positional argument.
-    pub fn get_pos_opt<E: ExpressionKind>(&mut self) -> ParseResult<Option<E>> {
-        Ok(if !self.positional.items.is_empty() {
-            let spanned = self.positional.items.remove(0);
-            Some(E::from_expr(spanned)?)
-        } else {
-            None
-        })
-    }
-
-    /// Add a keyword argument.
-    pub fn add_key(&mut self, key: Spanned<Ident>, value: Spanned<Expression>) {
-        self.keyword.add(key, value);
-    }
-
-    /// Add a keyword argument from an existing pair.
-    pub fn add_key_pair(&mut self, pair: Pair) {
-        self.keyword.add_pair(pair);
-    }
-
-    /// Force-extract a keyword argument.
-    pub fn get_key<E: ExpressionKind>(&mut self, name: &str) -> ParseResult<E> {
-        expect(self.get_key_opt(name))
-    }
-
-    /// Extract a keyword argument.
-    pub fn get_key_opt<E: ExpressionKind>(&mut self, name: &str) -> ParseResult<Option<E>> {
-        self.keyword.pairs.iter()
-            .position(|p| p.key.v.0 == name)
-            .map(|index| {
-                let value = self.keyword.pairs.swap_remove(index).value;
-                E::from_expr(value)
-            })
-            .transpose()
-    }
-
-    /// Iterator over positional arguments.
-    pub fn iter_pos(&mut self) -> std::vec::IntoIter<Spanned<Expression>> {
-        let tuple = std::mem::replace(&mut self.positional, Tuple::new());
-        tuple.items.into_iter()
-    }
-
-    /// Iterator over all keyword arguments.
-    pub fn iter_keys(&mut self) -> std::vec::IntoIter<Pair> {
-        let object = std::mem::replace(&mut self.keyword, Object::new());
-        object.pairs.into_iter()
-    }
-
-    /// Clear the argument lists.
-    pub fn clear(&mut self) {
-        self.positional.items.clear();
-        self.keyword.pairs.clear();
-    }
-
-    /// Whether both the positional and keyword argument lists are empty.
-    pub fn is_empty(&self) -> bool {
-        self.positional.items.is_empty() && self.keyword.pairs.is_empty()
-    }
-}
-
-/// Extract the option expression kind from the option or return an error.
-fn expect<E: ExpressionKind>(opt: ParseResult<Option<E>>) -> ParseResult<E> {
-    match opt {
-        Ok(Some(spanned)) => Ok(spanned),
-        Ok(None) => error!("expected {}", E::NAME),
-        Err(e) => Err(e),
-    }
-}
-
 /// Parses source code into a syntax tree given a context.
-pub fn parse(src: &str, ctx: ParseContext) -> SyntaxTree {
+pub fn parse(src: &str, ctx: ParseContext) -> (SyntaxTree, Colorization, ErrorMap) {
     Parser::new(src, ctx).parse()
 }
 
@@ -155,16 +18,13 @@ pub struct ParseContext<'a> {
 struct Parser<'s> {
     src: &'s str,
     ctx: ParseContext<'s>,
-    tokens: Peekable<Tokens<'s>>,
-    errors: Vec<Spanned<String>>,
-    colored: Vec<Spanned<ColorToken>>,
-    span: Span,
-}
+    colorization: Colorization,
+    error_map: ErrorMap,
 
-macro_rules! defer {
-    ($($tts:tt)*) => (
-        unimplemented!()
-    );
+    tokens: Tokens<'s>,
+    peeked: Option<Option<Spanned<Token<'s>>>>,
+    position: Position,
+    last_position: Position,
 }
 
 impl<'s> Parser<'s> {
@@ -172,81 +32,128 @@ impl<'s> Parser<'s> {
         Parser {
             src,
             ctx,
-            tokens: Tokens::new(src).peekable(),
-            errors: vec![],
-            colored: vec![],
-            span: Span::ZERO,
+            error_map: ErrorMap { errors: vec![] },
+            colorization: Colorization { colors: vec![] },
+
+            tokens: Tokens::new(src),
+            peeked: None,
+            position: Position::ZERO,
+            last_position: Position::ZERO,
         }
     }
 
-    fn parse(mut self) -> SyntaxTree {
+    fn parse(mut self) -> (SyntaxTree, Colorization, ErrorMap) {
         let mut tree = SyntaxTree::new();
 
         loop {
-            self.skip_whitespace();
+            if let Some(spanned) = self.eat() {
+                match spanned.v {
+                    LineComment(_) | BlockComment(_) => {}
 
-            let start = self.position();
+                    Whitespace(newlines) => {
+                        tree.add(spanned.map_v(if newlines >= 2 {
+                            Node::Newline
+                        } else {
+                            Node::Space
+                        }));
+                    }
 
-            let node = match self.next() {
-                Some(LeftBracket) => self.parse_func().map(|f| Node::Func(f)),
-                Some(Star) => Some(Node::ToggleBolder),
-                Some(Underscore) => Some(Node::ToggleItalic),
-                Some(Backtick) => Some(Node::ToggleMonospace),
-                Some(Text(text)) => Some(Node::Text(text.to_owned())),
-                Some(other) => { self.unexpected(other); None },
-                None => break,
-            };
+                    LeftBracket => {
+                        if let Some(func) = self.parse_func() {
+                            tree.add(func);
+                        }
+                    }
 
-            if let Some(node) = node {
-                let end = self.position();
-                let span = Span { start, end };
+                    Star       => tree.add(spanned.map_v(Node::ToggleBolder)),
+                    Underscore => tree.add(spanned.map_v(Node::ToggleItalic)),
+                    Backtick   => tree.add(spanned.map_v(Node::ToggleMonospace)),
+                    Text(text) => tree.add(spanned.map_v(Node::Text(text.to_owned()))),
 
-                tree.nodes.push(Spanned { v: node, span });
+                    _ => self.unexpected(spanned),
+                }
+            } else {
+                break;
             }
         }
 
-        tree
+        (tree, self.colorization, self.error_map)
     }
 
-    fn parse_func(&mut self) -> Option<FuncCall> {
-        let (name, args) = self.parse_func_header()?;
-        self.parse_func_call(name, args)
+    fn parse_func(&mut self) -> Option<Spanned<Node>> {
+        let start = self.last_pos();
+
+        let header = self.parse_func_header();
+        let call = self.parse_func_call(header)?;
+
+        let end = self.pos();
+        let span = Span { start, end };
+
+        Some(Spanned { v: Node::Func(call), span })
     }
 
-    fn parse_func_header(&mut self) -> Option<(Spanned<Ident>, FuncArgs)> {
-        defer! { self.eat_until(|t| t == RightBracket, true); }
-
+    fn parse_func_header(&mut self) -> Option<FuncHeader> {
         self.skip_whitespace();
 
-        let name = self.parse_func_name()?;
+        let name = self.parse_func_name().or_else(|| {
+            self.eat_until(|t| t == RightBracket, true);
+            None
+        })?;
 
         self.skip_whitespace();
-
-        let args = match self.next() {
-            Some(Colon) => self.parse_func_args(),
-            Some(RightBracket) => FuncArgs::new(),
+        let args = match self.eat() {
+            Some(Spanned { v: Colon, .. }) => self.parse_func_args(),
+            Some(Spanned { v: RightBracket, .. }) => FuncArgs::new(),
             other => {
                 self.expected("colon or closing bracket", other);
+                self.eat_until(|t| t == RightBracket, true);
                 FuncArgs::new()
             }
         };
 
-        Some((name, args))
+        Some(FuncHeader { name, args })
     }
 
-    fn parse_func_call(
-        &mut self,
-        name: Spanned<Ident>,
-        args: FuncArgs,
-    ) -> Option<FuncCall> {
-        unimplemented!()
+    fn parse_func_call(&mut self, header: Option<FuncHeader>) -> Option<FuncCall> {
+        println!("peek: {:?}", self.peek());
+
+        let body = if self.peek() == Some(LeftBracket) {
+            self.eat();
+
+            let start = self.tokens.index();
+            let found = self.tokens.move_to_closing_bracket();
+            let end = self.tokens.index();
+
+            self.last_position = self.position;
+            self.position = self.tokens.pos();
+
+            let body = &self.src[start .. end];
+
+            if found {
+                assert_eq!(self.eat().map(Spanned::value), Some(RightBracket));
+            } else {
+                self.error_here("expected closing bracket");
+            }
+
+            Some(body)
+        } else {
+            None
+        };
+
+        let header = header?;
+        let name = header.name;
+        let parser = self.ctx.scope.get_parser(name.v.as_str()).or_else(|| {
+            self.error(format!("unknown function: `{}`", name.v), name.span);
+            None
+        })?;
+
+        Some(FuncCall(parser(header.args, body, self.ctx).unwrap()))
     }
 
     fn parse_func_name(&mut self) -> Option<Spanned<Ident>> {
-        match self.next() {
-            Some(ExprIdent(ident)) => {
-                self.color_span(ColorToken::FuncName, self.span(), true);
-                Some(Spanned { v: Ident(ident.to_string()), span: self.span() })
+        match self.eat() {
+            Some(Spanned { v: ExprIdent(ident), span }) => {
+                self.color(Spanned { v: ColorToken::FuncName, span }, true);
+                Some(Spanned { v: Ident(ident.to_string()), span })
             }
             other => {
                 self.expected("identifier", other);
@@ -256,119 +163,16 @@ impl<'s> Parser<'s> {
     }
 
     fn parse_func_args(&mut self) -> FuncArgs {
-        enum State {
-            Start,
-            Identifier(Spanned<Ident>),
-            Assignment(Spanned<Ident>),
-            Value,
-        }
-
-        impl State {
-            fn expected(&self) -> &'static str {
-                match self {
-                    State::Start => "value or key",
-                    State::Identifier(_) => "comma or assignment",
-                    State::Assignment(_) => "value",
-                    State::Value => "comma",
-                }
-            }
-        }
-
-        let mut args = FuncArgs::new();
-        let mut state = State::Start;
-
-        loop {
-            self.skip_whitespace();
-
-            /*
-            let token = self.next();
-            match token {
-                Some(ExprIdent(ident)) => match state {
-                    State::Start => {
-                        state = State::Identifier(Spanned {
-                            v: Ident(ident.to_string()),
-                            span: self.span(),
-                        });
-                    }
-                    State::Identifier(prev) => {
-                        self.expected(state.expected(), token);
-                        args.add_pos(prev.map(|id| Expression::Ident(id)));
-                        state = State::Identifier(Spanned {
-                            v: Ident(ident.to_string()),
-                            span: self.span(),
-                        });
-                    }
-                    State::Assignment(key) => {
-                        let span = Span::merge(key.span, self.span());
-                        args.add_key(Spanned::new(KeyArg {
-                            key,
-                            value: Spanned {
-                                v: Expression::Ident(Ident(ident.to_string())),
-                                span: self.span(),
-                            },
-                        }, span));
-                        state = State::Value;
-                    }
-                    State::Value => {
-                        self.expected(state.expected(), token);
-                        state = State::Identifier(Spanned {
-                            v: Ident(ident.to_string()),
-                            span: self.span(),
-                        });
-                    }
-                }
-
-                // Handle expressions.
-                Some(Expr(_)) | Some(LeftParen) | Some(LeftBrace) => {
-                    let expr = match token.unwrap() {
-                        Expr(e) => e,
-                        LeftParen => self.parse_tuple(),
-                        LeftBrace => self.parse_object(),
-                        _ => unreachable!(),
-                    }
-                }
-
-                // Handle commas after values.
-                Some(Comma) => match state {
-                    State::Identifier(ident) => {
-                        args.add_pos(ident.map(|id| Expression::Ident(id)));
-                        state = State::Start;
-                    }
-                    State::Value => state = State::Start,
-                    _ => self.expected(state.expected(), token),
-                }
-
-                // Handle the end of the function header.
-                Some(RightBracket) => {
-                    match state {
-                        State::Identifier(ident) => {
-                            args.add_pos(ident.map(|id| Expression::Ident(id)));
-                        }
-                        State::Assignment(_) => {
-                            self.expected(state.expected(), token);
-                        }
-                        _ => {}
-                    }
-
-                    break;
-                }
-            }
-            */
-        }
-
-        args
+        // unimplemented!()
+        FuncArgs::new()
     }
 
-    fn handle_expr(&mut self, expr: Spanned<Expression>) {
-
+    fn parse_tuple(&mut self) -> Spanned<Expression> {
+        unimplemented!("parse_tuple")
     }
 
-    fn parse_tuple(&mut self) -> Spanned<Tuple> {
-        unimplemented!()
-    }
-
-    fn parse_object(&mut self) -> Spanned<Object> {
-        unimplemented!()
+    fn parse_object(&mut self) -> Spanned<Expression> {
+        unimplemented!("parse_object")
     }
 
     fn skip_whitespace(&mut self) {
@@ -378,68 +182,52 @@ impl<'s> Parser<'s> {
         }, false)
     }
 
-    fn eat_until<F>(&mut self, mut f: F, eat_match: bool)
-    where F: FnMut(Token<'s>) -> bool {
-        while let Some(token) = self.tokens.peek() {
-            if f(token.v) {
-                if eat_match {
-                    self.next();
-                }
-                break;
-            }
-
-            self.next();
+    fn expected(&mut self, thing: &str, found: Option<Spanned<Token>>) {
+        if let Some(Spanned { v: found, span }) = found {
+            self.error(
+                format!("expected {}, found {}", thing, name(found)),
+                span
+            );
+        } else {
+            self.error_here(format!("expected {}", thing));
         }
     }
 
-    fn next(&mut self) -> Option<Token<'s>> {
-        self.tokens.next().map(|spanned| {
-            self.color_token(&spanned.v, spanned.span);
-            self.span = spanned.span;
-            spanned.v
-        })
+    fn unexpected(&mut self, found: Spanned<Token>) {
+        self.error_map.errors.push(found.map(|t| format!("unexpected {}", name(t))));
     }
 
-    fn span(&self) -> Span {
-        self.span
+    fn error(&mut self, message: impl Into<String>, span: Span) {
+        self.error_map.errors.push(Spanned { v: message.into(), span });
     }
 
-    fn position(&self) -> Position {
-        self.span.end
+    fn error_here(&mut self, message: impl Into<String>) {
+        self.error(message, Span::at(self.pos()));
     }
 
-    fn unexpected(&mut self, found: Token) {
-        self.errors.push(Spanned {
-            v: format!("unexpected {}", name(found)),
-            span: self.span(),
-        });
+    fn color(&mut self, token: Spanned<ColorToken>, replace_last: bool) {
+        if replace_last {
+            if let Some(last) = self.colorization.colors.last_mut() {
+                *last = token;
+                return;
+            }
+        }
+
+        self.colorization.colors.push(token);
     }
 
-    fn expected(&mut self, thing: &str, found: Option<Token>) {
-        let message = if let Some(found) = found {
-            format!("expected {}, found {}", thing, name(found))
-        } else {
-            format!("expected {}", thing)
-        };
-
-        self.errors.push(Spanned {
-            v: message,
-            span: self.span(),
-        });
-    }
-
-    fn color_token(&mut self, token: &Token<'s>, span: Span) {
-        let colored = match token {
+    fn color_token(&mut self, token: Spanned<Token<'s>>) {
+        let colored = match token.v {
             LineComment(_) | BlockComment(_) => Some(ColorToken::Comment),
-            StarSlash => Some(ColorToken::Invalid),
+            StarSlash                  => Some(ColorToken::Invalid),
             LeftBracket | RightBracket => Some(ColorToken::Bracket),
             LeftParen | RightParen     => Some(ColorToken::Paren),
             LeftBrace | RightBrace     => Some(ColorToken::Brace),
-            Colon  => Some(ColorToken::Colon),
-            Comma  => Some(ColorToken::Comma),
-            Equals => Some(ColorToken::Equals),
-            ExprIdent(_)  =>  Some(ColorToken::ExprIdent),
-            ExprStr(_) => Some(ColorToken::ExprStr),
+            Colon         => Some(ColorToken::Colon),
+            Comma         => Some(ColorToken::Comma),
+            Equals        => Some(ColorToken::Equals),
+            ExprIdent(_)  => Some(ColorToken::ExprIdent),
+            ExprStr(_)    => Some(ColorToken::ExprStr),
             ExprNumber(_) => Some(ColorToken::ExprNumber),
             ExprSize(_)   => Some(ColorToken::ExprSize),
             ExprBool(_)   => Some(ColorToken::ExprBool),
@@ -447,21 +235,49 @@ impl<'s> Parser<'s> {
         };
 
         if let Some(color) = colored {
-            self.colored.push(Spanned { v: color, span });
+            self.colorization.colors.push(Spanned { v: color, span: token.span });
         }
     }
 
-    fn color_span(&mut self, color: ColorToken, span: Span, replace_last: bool) {
-        let token = Spanned { v: color, span };
-
-        if replace_last {
-            if let Some(last) = self.colored.last_mut() {
-                *last = token;
-                return;
+    fn eat_until<F>(&mut self, mut f: F, eat_match: bool)
+    where F: FnMut(Token<'s>) -> bool {
+        while let Some(token) = self.peek() {
+            if f(token) {
+                if eat_match {
+                    self.eat();
+                }
+                break;
             }
+
+            self.eat();
+        }
+    }
+
+    fn eat(&mut self) -> Option<Spanned<Token<'s>>> {
+        let token = self.peeked.take().unwrap_or_else(|| self.tokens.next());
+
+        self.last_position = self.position;
+        if let Some(spanned) = token {
+            self.color_token(spanned);
+            self.position = spanned.span.end;
         }
 
-        self.colored.push(token);
+        token
+    }
+
+    fn peek(&mut self) -> Option<Token<'s>> {
+        let iter = &mut self.tokens;
+        self.peeked
+            .get_or_insert_with(|| iter.next())
+            .map(Spanned::value)
+    }
+
+    fn pos(&self) -> Position {
+        self.position
+    }
+
+    fn last_pos(&self) -> Position {
+        self.last_position
     }
 }
 
diff --git a/src/syntax/tokens.rs b/src/syntax/tokens.rs
index 295a4382f..69d799654 100644
--- a/src/syntax/tokens.rs
+++ b/src/syntax/tokens.rs
@@ -6,64 +6,6 @@ use Token::*;
 use State::*;
 
 
-/// A minimal semantic entity of source code.
-#[derive(Debug, Copy, Clone, PartialEq)]
-pub enum Token<'s> {
-    /// One or more whitespace characters. The contained `usize` denotes the
-    /// number of newlines that were contained in the whitespace.
-    Whitespace(usize),
-
-    /// A line comment with inner string contents `//<&'s str>\n`.
-    LineComment(&'s str),
-    /// A block comment with inner string contents `/*<&'s str>*/`. The comment
-    /// can contain nested block comments.
-    BlockComment(&'s str),
-    /// An erroneous `*/` without an opening block comment.
-    StarSlash,
-
-    /// A left bracket: `[`.
-    LeftBracket,
-    /// A right bracket: `]`.
-    RightBracket,
-
-    /// A left parenthesis in a function header: `(`.
-    LeftParen,
-    /// A right parenthesis in a function header: `)`.
-    RightParen,
-    /// A left brace in a function header: `{`.
-    LeftBrace,
-    /// A right brace in a function header: `}`.
-    RightBrace,
-
-    /// A colon in a function header: `:`.
-    Colon,
-    /// A comma in a function header: `:`.
-    Comma,
-    /// An equals sign in a function header: `=`.
-    Equals,
-
-    /// An identifier in a function header: `center`.
-    ExprIdent(&'s str),
-    /// A quoted string in a function header: `"..."`.
-    ExprStr(&'s str),
-    /// A number in a function header: `3.14`.
-    ExprNumber(f64),
-    /// A size in a function header: `12pt`.
-    ExprSize(Size),
-    /// A boolean in a function header: `true | false`.
-    ExprBool(bool),
-
-    /// A star in body-text.
-    Star,
-    /// An underscore in body-text.
-    Underscore,
-    /// A backtick in body-text.
-    Backtick,
-
-    /// Any other consecutive string.
-    Text(&'s str),
-}
-
 /// Decomposes text into a sequence of semantic tokens.
 pub fn tokenize(src: &str) -> Tokens {
     Tokens::new(src)
@@ -97,6 +39,47 @@ impl<'s> Tokens<'s> {
             index: 0,
         }
     }
+
+    /// The index in the string at which the last token ends and next token will
+    /// start.
+    pub fn index(&self) -> usize {
+        self.index
+    }
+
+    /// The line-colunn position in the source at which the last token ends and
+    /// next token will start.
+    pub fn pos(&self) -> Position {
+        self.position
+    }
+
+    /// Move through the string until an unbalanced closing bracket is found
+    /// without tokenizing the contents.
+    ///
+    /// Returns whether a closing bracket was found or the end of the string was
+    /// reached.
+    pub fn move_to_closing_bracket(&mut self) -> bool {
+        let mut escaped = false;
+        let mut depth = 0;
+
+        self.read_string_until(|n| {
+            match n {
+                '[' if !escaped => depth += 1,
+                ']' if !escaped => {
+                    if depth == 0 {
+                        return true;
+                    } else {
+                        depth -= 1;
+                    }
+                }
+                '\\' => escaped = !escaped,
+                _ => escaped = false,
+            }
+
+            false
+        }, false, 0, 0);
+
+        self.peek() == Some(']')
+    }
 }
 
 impl<'s> Iterator for Tokens<'s> {
@@ -118,8 +101,13 @@ impl<'s> Iterator for Tokens<'s> {
 
             // Functions.
             '[' => {
-                self.stack.push(self.state);
-                self.state = Header;
+                if self.state == Header || self.state == Body {
+                    self.stack.push(self.state);
+                    self.state = Header;
+                } else {
+                    self.state = Body;
+                }
+
                 LeftBracket
             }
             ']' => {
@@ -221,12 +209,10 @@ impl<'s> Tokens<'s> {
     fn parse_string(&mut self) -> Token<'s> {
         let mut escaped = false;
         ExprStr(self.read_string_until(|n| {
-            if n == '"' && !escaped {
-                return true;
-            } else if n == '\\' {
-                escaped = !escaped;
-            } else {
-                escaped = false;
+            match n {
+                '"' if !escaped => return true,
+                '\\' => escaped = !escaped,
+                _ => escaped = false,
             }
 
             false
@@ -316,14 +302,6 @@ impl<'s> Tokens<'s> {
     fn peek(&mut self) -> Option<char> {
         self.iter.peek().copied()
     }
-
-    fn index(&self) -> usize {
-        self.index
-    }
-
-    fn pos(&self) -> Position {
-        self.position
-    }
 }
 
 fn parse_percentage(text: &str) -> Option<f64> {
diff --git a/tests/parse.rs b/tests/parse.rs
index 3e46dd4a1..616f4d70b 100644
--- a/tests/parse.rs
+++ b/tests/parse.rs
@@ -1,47 +1,159 @@
 #![allow(unused_imports)]
+#![allow(dead_code)]
 #![allow(non_snake_case)]
 
+use typstc::func::Scope;
 use typstc::size::Size;
 use typstc::syntax::*;
-use Token::{
-    Whitespace as W,
-    LineComment as LC, BlockComment as BC, StarSlash as SS,
-    LeftBracket as LB, RightBracket as RB,
-    LeftParen as LP, RightParen as RP,
-    LeftBrace as LBR, RightBrace as RBR,
-    Colon as CL, Comma as CM, Equals as EQ,
-    ExprIdent as ID, ExprStr as STR, ExprSize as SIZE,
-    ExprNumber as NUM, ExprBool as BOOL,
-    Star as ST, Underscore as U, Backtick as B, Text as T,
-};
+use typstc::{function, parse};
+
+
+mod token_shorthands {
+    pub use super::Token::{
+        Whitespace as W,
+        LineComment as LC, BlockComment as BC, StarSlash as SS,
+        LeftBracket as LB, RightBracket as RB,
+        LeftParen as LP, RightParen as RP,
+        LeftBrace as LBR, RightBrace as RBR,
+        Colon as CL, Comma as CM, Equals as EQ,
+        ExprIdent as ID, ExprStr as STR, ExprSize as SIZE,
+        ExprNumber as NUM, ExprBool as BOOL,
+        Star as ST, Underscore as U, Backtick as B, Text as T,
+    };
+}
+
+mod node_shorthands {
+    use super::Node;
+    pub use Node::{
+        Space as S, Newline as N, Text,
+        ToggleItalic as I, ToggleBolder as B, ToggleMonospace as M,
+        Func,
+    };
+    pub fn T(text: &str) -> Node { Node::Text(text.to_string()) }
+}
+
+macro_rules! F {
+    (@body None) => (None);
+    (@body Some([$($tts:tt)*])) => ({
+        let nodes = vec![$($tts)*].into_iter()
+            .map(|v| Spanned { v, span: Span::ZERO })
+            .collect();
+
+        Some(SyntaxTree { nodes })
+    });
+
+    ($($body:tt)*) => ({
+        Func(FuncCall(Box::new(DebugFn {
+            pos: vec![],
+            key: vec![],
+            body: F!(@body $($body)*),
+        })))
+    });
+}
+
+function! {
+    #[derive(Debug, PartialEq)]
+    pub struct DebugFn {
+        pos: Vec<Spanned<Expression>>,
+        key: Vec<Pair>,
+        body: Option<SyntaxTree>,
+    }
+
+    parse(args, body, ctx) {
+        DebugFn {
+            pos: args.iter_pos().collect(),
+            key: args.iter_keys().collect(),
+            body: parse!(optional: body, ctx),
+        }
+    }
+
+    layout() { vec![] }
+}
+
+impl DebugFn {
+    fn compare(&self, other: &DebugFn) -> bool {
+        self.pos.iter().zip(&other.pos).all(|(a, b)| a.v == b.v)
+            && self.key.iter().zip(&other.key)
+                .all(|(a, b)| a.key.v == b.key.v && a.value.v == b.value.v)
+            && match (&self.body, &other.body) {
+                (Some(a), Some(b)) => compare(a, b),
+                (None, None) => true,
+                _ => false,
+            }
+    }
+}
+
+fn downcast(func: &FuncCall) -> &DebugFn {
+    func.0.downcast::<DebugFn>().expect("not a debug fn")
+}
+
+fn compare(a: &SyntaxTree, b: &SyntaxTree) -> bool {
+    for (x, y) in a.nodes.iter().zip(&b.nodes) {
+        use node_shorthands::*;
+        let same = match (&x.v, &y.v) {
+            (S, S) | (N, N) | (I, I) | (B, B) | (M, M) => true,
+            (Text(t1), Text(t2)) => t1 == t2,
+            (Func(f1), Func(f2)) => {
+                downcast(f1).compare(downcast(f2))
+            }
+            _ => false,
+        };
+
+        if !same { return false; }
+    }
+    true
+}
 
 /// Parses the test syntax.
 macro_rules! tokens {
-    ($($task:ident $src:expr =>($line:expr)=> [$($target:tt)*])*) => ({
+    ($($task:ident $src:expr =>($line:expr)=> [$($tts:tt)*])*) => ({
         #[allow(unused_mut)]
         let mut cases = Vec::new();
-        $(cases.push(($line, $src, tokens!(@$task [$($target)*])));)*
+        $(cases.push(($line, $src, tokens!(@$task [$($tts)*])));)*
         cases
     });
 
-    (@t $tokens:expr) => ({
-        Target::Tokenized($tokens.to_vec())
+    (@t [$($tts:tt)*]) => ({
+        use token_shorthands::*;
+        Target::Tokenize(vec![$($tts)*])
     });
 
-    (@ts [$(($sl:tt:$sc:tt, $el:tt:$ec:tt, $t:expr)),* $(,)?]) => ({
-        Target::TokenizedSpanned(vec![
-            $(Spanned { v: $t, span: Span {
+    (@ts [$($tts:tt)*]) => ({
+        use token_shorthands::*;
+        Target::TokenizeSpanned(tokens!(@__spans [$($tts)*]))
+    });
+
+    (@p [$($tts:tt)*]) => ({
+        use node_shorthands::*;
+
+        let nodes = vec![$($tts)*].into_iter()
+            .map(|v| Spanned { v, span: Span::ZERO })
+            .collect();
+
+        Target::Parse(SyntaxTree { nodes })
+    });
+
+    (@ps [$($tts:tt)*]) => ({
+        use node_shorthands::*;
+        Target::ParseSpanned(tokens!(@__spans [$($tts)*]))
+    });
+
+    (@__spans [$(($sl:tt:$sc:tt, $el:tt:$ec:tt, $v:expr)),* $(,)?]) => ({
+        vec![
+            $(Spanned { v: $v, span: Span {
                 start: Position { line: $sl, column: $sc },
                 end:   Position { line: $el, column: $ec },
             }}),*
-        ])
+        ]
     });
 }
 
 #[derive(Debug)]
 enum Target {
-    Tokenized(Vec<Token<'static>>),
-    TokenizedSpanned(Vec<Spanned<Token<'static>>>),
+    Tokenize(Vec<Token<'static>>),
+    TokenizeSpanned(Vec<Spanned<Token<'static>>>),
+    Parse(SyntaxTree),
+    ParseSpanned(SyntaxTree),
 }
 
 fn main() {
@@ -75,6 +187,7 @@ fn main() {
                 println!("   - Source:   {:?}", src);
                 println!("   - Expected: {:?}", expected);
                 println!("   - Found:    {:?}", found);
+                println!();
 
                 failed += 1;
                 errors = true;
@@ -98,14 +211,26 @@ fn main() {
 
 fn test_case(src: &str, target: Target) -> (bool, String, String) {
     match target {
-        Target::Tokenized(tokens) => {
+        Target::Tokenize(tokens) => {
             let found: Vec<_> = tokenize(src).map(Spanned::value).collect();
             (found == tokens, format!("{:?}", tokens), format!("{:?}", found))
         }
 
-        Target::TokenizedSpanned(tokens) => {
+        Target::TokenizeSpanned(tokens) => {
             let found: Vec<_> = tokenize(src).collect();
             (found == tokens, format!("{:?}", tokens), format!("{:?}", found))
         }
+
+        Target::Parse(tree) => {
+            let scope = Scope::with_debug::<DebugFn>();
+            let (found, _, errs) = parse(src, ParseContext { scope: &scope });
+            (compare(&tree, &found), format!("{:?}", tree), format!("{:?}", found))
+        }
+
+        Target::ParseSpanned(tree) => {
+            let scope = Scope::with_debug::<DebugFn>();
+            let (found, _, _) = parse(src, ParseContext { scope: &scope });
+            (tree == found, format!("{:?}", tree), format!("{:?}", found))
+        }
     }
 }
diff --git a/tests/parsing/tokens.rs b/tests/parsing/tokens.rs
index 78d891f97..14f4e521e 100644
--- a/tests/parsing/tokens.rs
+++ b/tests/parsing/tokens.rs
@@ -46,6 +46,12 @@ t "[func]*bold*"  => [LB, ID("func"), RB, ST, T("bold"), ST]
 t "[_*`]"         => [LB, T("_"), T("*"), T("`"), RB]
 t "hi_you_ there" => [T("hi"), U, T("you"), U, W(0), T("there")]
 
+// Nested functions.
+t "[f: [=][*]]"    => [LB, ID("f"), CL, W(0), LB, EQ, RB, LB, ST, RB, RB]
+t "[_][[,],],"     => [LB, T("_"), RB, LB, LB, CM, RB, T(","), RB, T(",")]
+t "[=][=][=]"      => [LB, EQ, RB, LB, T("="), RB, LB, EQ, RB]
+t "[=][[=][=][=]]" => [LB, EQ, RB, LB, LB, EQ, RB, LB, T("="), RB, LB, EQ, RB, RB]
+
 // Escapes.
 t r"\["   => [T("[")]
 t r"\]"   => [T("]")]
@@ -68,7 +74,7 @@ ts "ab\r\nc"         => [(0:0, 0:2, T("ab")), (0:2, 1:0, W(1)), (1:0, 1:1, T("c"
 ts "[a=10]"          => [(0:0, 0:1, LB), (0:1, 0:2, ID("a")), (0:2, 0:3, EQ),
                          (0:3, 0:5, NUM(10.0)), (0:5, 0:6, RB)]
 ts r#"[x = "(1)"]*"# => [(0:0, 0:1, LB), (0:1, 0:2, ID("x")), (0:2, 0:3, W(0)),
-                        (0:3, 0:4, EQ), (0:4, 0:5, W(0)), (0:5, 0:10, STR("(1)")),
-                        (0:10, 0:11, RB), (0:11, 0:12, ST)]
+                         (0:3, 0:4, EQ), (0:4, 0:5, W(0)), (0:5, 0:10, STR("(1)")),
+                         (0:10, 0:11, RB), (0:11, 0:12, ST)]
 ts "// ab\r\n\nf"    => [(0:0, 0:5, LC(" ab")), (0:5, 2:0, W(2)), (2:0, 2:1, T("f"))]
 ts "/*b*/_"          => [(0:0, 0:5, BC("b")), (0:5, 0:6, U)]
diff --git a/tests/parsing/trees.rs b/tests/parsing/trees.rs
new file mode 100644
index 000000000..78b168286
--- /dev/null
+++ b/tests/parsing/trees.rs
@@ -0,0 +1,20 @@
+p "" => []
+p "hi" => [T("hi")]
+p "hi you" => [T("hi"), S, T("you")]
+p "❤\n\n 🌍" => [T("❤"), N, T("🌍")]
+p "[func]" => [F!(None)]
+p "[tree][hi *you*]" => [F!(Some([T("hi"), S, B, T("you"), B]))]
+// p "from [align: left] to" => [
+//     T("from"), S,
+//     F!("align", pos=[ID("left")], None),
+//     S, T("to"),
+// ]
+// p "[box: x=1.2pt, false][a b c] bye" => [
+//     F!(
+//         "box",
+//         pos=[BOOL(false)],
+//         key=["x": SIZE(Size::pt(1.2))],
+//         Some([T("a"), S, T("b"), S, T("c")]),
+//     ),
+//     S, T("bye"),
+// ]