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diff --git a/src/syntax.rs b/src/syntax.rs
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+//! Token and abstract syntax tree representations.
+
+
+/// A logical unit of the incoming text stream.
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum Token<'s> {
+    /// One or more whitespace (non-newline) codepoints.
+    Space,
+    /// A line feed (either `\n` or `\r\n`).
+    Newline,
+    /// A left bracket: `[`.
+    LeftBracket,
+    /// A right bracket: `]`.
+    RightBracket,
+    /// A colon (`:`) indicating the beginning of function arguments.
+    ///
+    /// If a colon occurs outside of the function header, it will be
+    /// tokenized as a [Word](Token::Word).
+    Colon,
+    /// Same as with [Colon](Token::Colon).
+    Equals,
+    /// Two underscores, indicating text in _italics_.
+    DoubleUnderscore,
+    /// Two stars, indicating **bold** text.
+    DoubleStar,
+    /// A dollar sign, indicating _mathematical_ content.
+    Dollar,
+    /// A hashtag starting a _comment_.
+    Hashtag,
+    /// Everything else just is a literal word.
+    Word(&'s str),
+}
+
+/// A tree representation of the source.
+#[derive(Debug, Clone, PartialEq)]
+pub struct SyntaxTree<'s> {
+    /// The children.
+    pub nodes: Vec<Node<'s>>,
+}
+
+impl<'s> SyntaxTree<'s> {
+    /// Create an empty syntax tree.
+    #[inline]
+    pub fn new() -> SyntaxTree<'s> {
+        SyntaxTree { nodes: vec![] }
+    }
+}
+
+/// A node in the abstract syntax tree.
+#[derive(Debug, Clone, PartialEq)]
+pub enum Node<'s> {
+    /// Whitespace between other nodes.
+    Space,
+    /// A line feed.
+    Newline,
+    /// Indicates that italics were enabled/disabled.
+    ToggleItalics,
+    /// Indicates that boldface was enabled/disabled.
+    ToggleBold,
+    /// Indicates that math mode was enabled/disabled.
+    ToggleMath,
+    /// A literal word.
+    Word(&'s str),
+    /// A function invocation.
+    Func(Function<'s>),
+}
+
+/// A node representing a function invocation.
+#[derive(Debug, Clone, PartialEq)]
+pub struct Function<'s> {
+    /// The name of the function.
+    pub name: &'s str,
+    /// Some syntax tree if the function had a body (second set of brackets),
+    /// otherwise nothing.
+    pub body: Option<SyntaxTree<'s>>,
+}