1 files changed, 248 insertions, 0 deletions
diff --git a/src/syntax/expr.rs b/src/syntax/expr.rs
new file mode 100644
index 00000000..a1680861
--- /dev/null
+++ b/src/syntax/expr.rs
@@ -0,0 +1,248 @@
+use super::*;
+
+
+/// The arguments passed to a function.
+#[derive(Debug, Clone, PartialEq)]
+pub struct FuncArgs {
+    pub pos: Vec<Spanned<PosArg>>,
+    pub key: Vec<Spanned<KeyArg>>,
+}
+
+impl FuncArgs {
+    /// Create an empty collection of arguments.
+    pub fn new() -> FuncArgs {
+        FuncArgs {
+            pos: vec![],
+            key: vec![],
+        }
+    }
+
+    /// Add a positional argument.
+    pub fn add_pos(&mut self, arg: Spanned<PosArg>) {
+        self.pos.push(arg);
+    }
+
+    /// Add a keyword argument.
+    pub fn add_key(&mut self, arg: Spanned<KeyArg>) {
+        self.key.push(arg);
+    }
+
+    /// 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.pos.is_empty() {
+            let spanned = self.pos.remove(0);
+            Some(E::from_expr(spanned)?)
+        } else {
+            None
+        })
+    }
+
+    /// Iterator over positional arguments.
+    pub fn pos(&mut self) -> std::vec::IntoIter<Spanned<PosArg>> {
+        let vec = std::mem::replace(&mut self.pos, vec![]);
+        vec.into_iter()
+    }
+
+    /// 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>> {
+        Ok(if let Some(index) = self.key.iter().position(|arg| arg.v.key.v.0 == name) {
+            let value = self.key.swap_remove(index).v.value;
+            Some(E::from_expr(value)?)
+        } else {
+            None
+        })
+    }
+
+    /// Extract any keyword argument.
+    pub fn get_key_next(&mut self) -> Option<Spanned<KeyArg>> {
+        self.key.pop()
+    }
+
+    /// Iterator over all keyword arguments.
+    pub fn keys(&mut self) -> std::vec::IntoIter<Spanned<KeyArg>> {
+        let vec = std::mem::replace(&mut self.key, vec![]);
+        vec.into_iter()
+    }
+
+    /// Clear the argument lists.
+    pub fn clear(&mut self) {
+        self.pos.clear();
+        self.key.clear();
+    }
+
+    /// Whether both the positional and keyword argument lists are empty.
+    pub fn is_empty(&self) -> bool {
+        self.pos.is_empty() && self.key.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),
+    }
+}
+
+/// A positional argument passed to a function.
+pub type PosArg = Expression;
+
+/// A keyword argument passed to a function.
+#[derive(Debug, Clone, PartialEq)]
+pub struct KeyArg {
+    pub key: Spanned<Ident>,
+    pub value: Spanned<Expression>,
+}
+
+/// Either a positional or keyword argument.
+#[derive(Debug, Clone, PartialEq)]
+pub enum DynArg {
+    Pos(Spanned<PosArg>),
+    Key(Spanned<KeyArg>),
+}
+
+/// An argument or return value.
+#[derive(Clone, PartialEq)]
+pub enum Expression {
+    Ident(Ident),
+    Str(String),
+    Num(f64),
+    Size(Size),
+    Bool(bool),
+}
+
+impl Display for Expression {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        use Expression::*;
+        match self {
+            Ident(i) => write!(f, "{}", i),
+            Str(s) => write!(f, "{:?}", s),
+            Num(n) => write!(f, "{}", n),
+            Size(s) => write!(f, "{}", s),
+            Bool(b) => write!(f, "{}", b),
+        }
+    }
+}
+
+debug_display!(Expression);
+
+pub struct Tuple;
+pub struct Object;
+
+/// An identifier.
+#[derive(Clone, PartialEq)]
+pub struct Ident(pub String);
+
+impl Ident {
+    pub fn new<S>(ident: S) -> Option<Ident> where S: AsRef<str> + Into<String> {
+        if is_identifier(ident.as_ref()) {
+            Some(Ident(ident.into()))
+        } else {
+            None
+        }
+    }
+
+    pub fn as_str(&self) -> &str {
+        self.0.as_str()
+    }
+}
+
+impl Display for Ident {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+debug_display!(Ident);
+
+/// Whether this word is a valid identifier.
+pub fn is_identifier(string: &str) -> bool {
+    let mut chars = string.chars();
+
+    match chars.next() {
+        Some('-') => {}
+        Some(c) if UnicodeXID::is_xid_start(c) => {}
+        _ => return false,
+    }
+
+    while let Some(c) = chars.next() {
+        match c {
+            '.' | '-' => {}
+            c if UnicodeXID::is_xid_continue(c) => {}
+            _ => return false,
+        }
+    }
+
+    true
+}
+
+/// Kinds of expressions.
+pub trait ExpressionKind: Sized {
+    const NAME: &'static str;
+
+    /// Create from expression.
+    fn from_expr(expr: Spanned<Expression>) -> ParseResult<Self>;
+}
+
+macro_rules! kind {
+    ($type:ty, $name:expr, $($patterns:tt)*) => {
+        impl ExpressionKind for $type {
+            const NAME: &'static str = $name;
+
+            fn from_expr(expr: Spanned<Expression>) -> ParseResult<Self> {
+                #[allow(unreachable_patterns)]
+                Ok(match expr.v {
+                    $($patterns)*,
+                    _ => error!("expected {}", Self::NAME),
+                })
+            }
+        }
+    };
+}
+
+kind!(Expression, "expression", e                         => e);
+kind!(Ident,      "identifier", Expression::Ident(ident)  => ident);
+kind!(String,     "string",     Expression::Str(string)   => string);
+kind!(f64,        "number",     Expression::Num(num)      => num);
+kind!(bool,       "boolean",    Expression::Bool(boolean) => boolean);
+kind!(Size,       "size",       Expression::Size(size)    => size);
+kind!(ScaleSize,  "number or size",
+    Expression::Size(size) => ScaleSize::Absolute(size),
+    Expression::Num(scale) => ScaleSize::Scaled(scale as f32)
+);
+
+impl<T> ExpressionKind for Spanned<T> where T: ExpressionKind {
+    const NAME: &'static str = T::NAME;
+
+    fn from_expr(expr: Spanned<Expression>) -> ParseResult<Spanned<T>> {
+        let span = expr.span;
+        T::from_expr(expr)
+            .map(|v| Spanned::new(v, span))
+    }
+}
+
+impl<T> ExpressionKind for Option<T> where T: ExpressionKind {
+    const NAME: &'static str = T::NAME;
+
+    fn from_expr(expr: Spanned<Expression>) -> ParseResult<Option<T>> {
+        if let Expression::Ident(ident) = &expr.v {
+            match ident.as_str() {
+                "default" | "none" => return Ok(None),
+                _ => {},
+            }
+        }
+
+        T::from_expr(expr).map(|v| Some(v))
+    }
+}