1 files changed, 497 insertions, 0 deletions
diff --git a/src/eval/value.rs b/src/eval/value.rs
new file mode 100644
index 00000000..5e06da76
--- /dev/null
+++ b/src/eval/value.rs
@@ -0,0 +1,497 @@
+use std::any::Any;
+use std::cmp::Ordering;
+use std::fmt::{self, Debug, Formatter};
+use std::hash::{Hash, Hasher};
+use std::sync::Arc;
+
+use ecow::{eco_format, EcoString};
+use siphasher::sip128::{Hasher128, SipHasher};
+
+use super::{
+    format_str, ops, Args, Array, Cast, CastInfo, Content, Dict, Func, Label, Module,
+    Str, Symbol,
+};
+use crate::diag::StrResult;
+use crate::geom::{Abs, Angle, Color, Em, Fr, Length, Ratio, Rel, RgbaColor};
+use crate::syntax::{ast, Span};
+
+/// A computational value.
+#[derive(Clone)]
+pub enum Value {
+    /// The value that indicates the absence of a meaningful value.
+    None,
+    /// A value that indicates some smart default behaviour.
+    Auto,
+    /// 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`, `1.5em`, `1em - 2pt`.
+    Length(Length),
+    /// An angle: `1.5rad`, `90deg`.
+    Angle(Angle),
+    /// A ratio: `50%`.
+    Ratio(Ratio),
+    /// A relative length, combination of a ratio and a length: `20% + 5cm`.
+    Relative(Rel<Length>),
+    /// A fraction: `1fr`.
+    Fraction(Fr),
+    /// A color value: `#f79143ff`.
+    Color(Color),
+    /// A symbol: `arrow.l`.
+    Symbol(Symbol),
+    /// A string: `"string"`.
+    Str(Str),
+    /// A label: `<intro>`.
+    Label(Label),
+    /// A content value: `[*Hi* there]`.
+    Content(Content),
+    /// An array of values: `(1, "hi", 12cm)`.
+    Array(Array),
+    /// A dictionary value: `(color: #f79143, pattern: dashed)`.
+    Dict(Dict),
+    /// An executable function.
+    Func(Func),
+    /// Captured arguments to a function.
+    Args(Args),
+    /// A module.
+    Module(Module),
+    /// A dynamic value.
+    Dyn(Dynamic),
+}
+
+impl Value {
+    /// Create a new dynamic value.
+    pub fn dynamic<T>(any: T) -> Self
+    where
+        T: Type + Debug + PartialEq + Hash + Sync + Send + 'static,
+    {
+        Self::Dyn(Dynamic::new(any))
+    }
+
+    /// Create a numeric value from a number with a unit.
+    pub fn numeric(pair: (f64, ast::Unit)) -> Self {
+        let (v, unit) = pair;
+        match unit {
+            ast::Unit::Length(unit) => Abs::with_unit(v, unit).into(),
+            ast::Unit::Angle(unit) => Angle::with_unit(v, unit).into(),
+            ast::Unit::Em => Em::new(v).into(),
+            ast::Unit::Fr => Fr::new(v).into(),
+            ast::Unit::Percent => Ratio::new(v / 100.0).into(),
+        }
+    }
+
+    /// The name of the stored value's type.
+    pub fn type_name(&self) -> &'static str {
+        match self {
+            Self::None => "none",
+            Self::Auto => "auto",
+            Self::Bool(_) => bool::TYPE_NAME,
+            Self::Int(_) => i64::TYPE_NAME,
+            Self::Float(_) => f64::TYPE_NAME,
+            Self::Length(_) => Length::TYPE_NAME,
+            Self::Angle(_) => Angle::TYPE_NAME,
+            Self::Ratio(_) => Ratio::TYPE_NAME,
+            Self::Relative(_) => Rel::<Length>::TYPE_NAME,
+            Self::Fraction(_) => Fr::TYPE_NAME,
+            Self::Color(_) => Color::TYPE_NAME,
+            Self::Symbol(_) => Symbol::TYPE_NAME,
+            Self::Str(_) => Str::TYPE_NAME,
+            Self::Label(_) => Label::TYPE_NAME,
+            Self::Content(_) => Content::TYPE_NAME,
+            Self::Array(_) => Array::TYPE_NAME,
+            Self::Dict(_) => Dict::TYPE_NAME,
+            Self::Func(_) => Func::TYPE_NAME,
+            Self::Args(_) => Args::TYPE_NAME,
+            Self::Module(_) => Module::TYPE_NAME,
+            Self::Dyn(v) => v.type_name(),
+        }
+    }
+
+    /// Try to cast the value into a specific type.
+    pub fn cast<T: Cast>(self) -> StrResult<T> {
+        T::cast(self)
+    }
+
+    /// Try to access a field on the value.
+    pub fn field(&self, field: &str) -> StrResult<Value> {
+        match self {
+            Self::Symbol(symbol) => symbol.clone().modified(&field).map(Self::Symbol),
+            Self::Dict(dict) => dict.at(&field).cloned(),
+            Self::Content(content) => content
+                .field(&field)
+                .ok_or_else(|| eco_format!("unknown field `{field}`")),
+            Self::Module(module) => module.get(&field).cloned(),
+            v => Err(eco_format!("cannot access fields on type {}", v.type_name())),
+        }
+    }
+
+    /// Return the debug representation of the value.
+    pub fn repr(&self) -> Str {
+        format_str!("{:?}", self)
+    }
+
+    /// Attach a span to the value, if possible.
+    pub fn spanned(self, span: Span) -> Self {
+        match self {
+            Value::Content(v) => Value::Content(v.spanned(span)),
+            Value::Func(v) => Value::Func(v.spanned(span)),
+            v => v,
+        }
+    }
+
+    /// Return the display representation of the value.
+    pub fn display(self) -> Content {
+        match self {
+            Self::None => Content::empty(),
+            Self::Int(v) => item!(text)(eco_format!("{}", v)),
+            Self::Float(v) => item!(text)(eco_format!("{}", v)),
+            Self::Str(v) => item!(text)(v.into()),
+            Self::Symbol(v) => item!(text)(v.get().into()),
+            Self::Content(v) => v,
+            Self::Func(_) => Content::empty(),
+            Self::Module(module) => module.content(),
+            _ => item!(raw)(self.repr().into(), Some("typc".into()), false),
+        }
+    }
+
+    /// Try to extract documentation for the value.
+    pub fn docs(&self) -> Option<&'static str> {
+        match self {
+            Self::Func(func) => func.info().map(|info| info.docs),
+            _ => None,
+        }
+    }
+}
+
+impl Default for Value {
+    fn default() -> Self {
+        Value::None
+    }
+}
+
+impl Debug for Value {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        match self {
+            Self::None => f.pad("none"),
+            Self::Auto => f.pad("auto"),
+            Self::Bool(v) => Debug::fmt(v, f),
+            Self::Int(v) => Debug::fmt(v, f),
+            Self::Float(v) => Debug::fmt(v, f),
+            Self::Length(v) => Debug::fmt(v, f),
+            Self::Angle(v) => Debug::fmt(v, f),
+            Self::Ratio(v) => Debug::fmt(v, f),
+            Self::Relative(v) => Debug::fmt(v, f),
+            Self::Fraction(v) => Debug::fmt(v, f),
+            Self::Color(v) => Debug::fmt(v, f),
+            Self::Symbol(v) => Debug::fmt(v, f),
+            Self::Str(v) => Debug::fmt(v, f),
+            Self::Label(v) => Debug::fmt(v, f),
+            Self::Content(_) => f.pad("[...]"),
+            Self::Array(v) => Debug::fmt(v, f),
+            Self::Dict(v) => Debug::fmt(v, f),
+            Self::Func(v) => Debug::fmt(v, f),
+            Self::Args(v) => Debug::fmt(v, f),
+            Self::Module(v) => Debug::fmt(v, f),
+            Self::Dyn(v) => Debug::fmt(v, f),
+        }
+    }
+}
+
+impl PartialEq for Value {
+    fn eq(&self, other: &Self) -> bool {
+        ops::equal(self, other)
+    }
+}
+
+impl PartialOrd for Value {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        ops::compare(self, other)
+    }
+}
+
+impl Hash for Value {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        std::mem::discriminant(self).hash(state);
+        match self {
+            Self::None => {}
+            Self::Auto => {}
+            Self::Bool(v) => v.hash(state),
+            Self::Int(v) => v.hash(state),
+            Self::Float(v) => v.to_bits().hash(state),
+            Self::Length(v) => v.hash(state),
+            Self::Angle(v) => v.hash(state),
+            Self::Ratio(v) => v.hash(state),
+            Self::Relative(v) => v.hash(state),
+            Self::Fraction(v) => v.hash(state),
+            Self::Color(v) => v.hash(state),
+            Self::Symbol(v) => v.hash(state),
+            Self::Str(v) => v.hash(state),
+            Self::Label(v) => v.hash(state),
+            Self::Content(v) => v.hash(state),
+            Self::Array(v) => v.hash(state),
+            Self::Dict(v) => v.hash(state),
+            Self::Func(v) => v.hash(state),
+            Self::Args(v) => v.hash(state),
+            Self::Module(v) => v.hash(state),
+            Self::Dyn(v) => v.hash(state),
+        }
+    }
+}
+
+impl From<i32> for Value {
+    fn from(v: i32) -> Self {
+        Self::Int(v as i64)
+    }
+}
+
+impl From<usize> for Value {
+    fn from(v: usize) -> Self {
+        Self::Int(v as i64)
+    }
+}
+
+impl From<Abs> for Value {
+    fn from(v: Abs) -> Self {
+        Self::Length(v.into())
+    }
+}
+
+impl From<Em> for Value {
+    fn from(v: Em) -> Self {
+        Self::Length(v.into())
+    }
+}
+
+impl From<RgbaColor> for Value {
+    fn from(v: RgbaColor) -> Self {
+        Self::Color(v.into())
+    }
+}
+
+impl From<&str> for Value {
+    fn from(v: &str) -> Self {
+        Self::Str(v.into())
+    }
+}
+
+impl From<EcoString> for Value {
+    fn from(v: EcoString) -> Self {
+        Self::Str(v.into())
+    }
+}
+
+impl From<String> for Value {
+    fn from(v: String) -> Self {
+        Self::Str(v.into())
+    }
+}
+
+impl From<Dynamic> for Value {
+    fn from(v: Dynamic) -> Self {
+        Self::Dyn(v)
+    }
+}
+
+/// A dynamic value.
+#[derive(Clone, Hash)]
+pub struct Dynamic(Arc<dyn Bounds>);
+
+impl Dynamic {
+    /// Create a new instance from any value that satisifies the required bounds.
+    pub fn new<T>(any: T) -> Self
+    where
+        T: Type + Debug + PartialEq + Hash + Sync + Send + 'static,
+    {
+        Self(Arc::new(any))
+    }
+
+    /// Whether the wrapped type is `T`.
+    pub fn is<T: Type + 'static>(&self) -> bool {
+        (*self.0).as_any().is::<T>()
+    }
+
+    /// Try to downcast to a reference to a specific type.
+    pub fn downcast<T: Type + 'static>(&self) -> Option<&T> {
+        (*self.0).as_any().downcast_ref()
+    }
+
+    /// The name of the stored value's type.
+    pub fn type_name(&self) -> &'static str {
+        self.0.dyn_type_name()
+    }
+}
+
+impl Debug for Dynamic {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        Debug::fmt(&self.0, f)
+    }
+}
+
+impl PartialEq for Dynamic {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.dyn_eq(other)
+    }
+}
+
+trait Bounds: Debug + Sync + Send + 'static {
+    fn as_any(&self) -> &dyn Any;
+    fn dyn_eq(&self, other: &Dynamic) -> bool;
+    fn dyn_type_name(&self) -> &'static str;
+    fn hash128(&self) -> u128;
+}
+
+impl<T> Bounds for T
+where
+    T: Type + Debug + PartialEq + Hash + Sync + Send + 'static,
+{
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn dyn_eq(&self, other: &Dynamic) -> bool {
+        let Some(other) = other.downcast::<Self>() else { return false };
+        self == other
+    }
+
+    fn dyn_type_name(&self) -> &'static str {
+        T::TYPE_NAME
+    }
+
+    fn hash128(&self) -> u128 {
+        // Also hash the TypeId since values with different types but
+        // equal data should be different.
+        let mut state = SipHasher::new();
+        self.type_id().hash(&mut state);
+        self.hash(&mut state);
+        state.finish128().as_u128()
+    }
+}
+
+impl Hash for dyn Bounds {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        state.write_u128(self.hash128());
+    }
+}
+
+/// The type of a value.
+pub trait Type {
+    /// The name of the type.
+    const TYPE_NAME: &'static str;
+}
+
+/// Implement traits for primitives.
+macro_rules! primitive {
+    (
+        $type:ty: $name:literal, $variant:ident
+        $(, $other:ident$(($binding:ident))? => $out:expr)*
+    ) => {
+        impl Type for $type {
+            const TYPE_NAME: &'static str = $name;
+        }
+
+        impl Cast for $type {
+            fn is(value: &Value) -> bool {
+                matches!(value, Value::$variant(_)
+                    $(|  primitive!(@$other $(($binding))?))*)
+            }
+
+            fn cast(value: Value) -> StrResult<Self> {
+                match value {
+                    Value::$variant(v) => Ok(v),
+                    $(Value::$other$(($binding))? => Ok($out),)*
+                    v => Err(eco_format!(
+                        "expected {}, found {}",
+                        Self::TYPE_NAME,
+                        v.type_name(),
+                    )),
+                }
+            }
+
+            fn describe() -> CastInfo {
+                CastInfo::Type(Self::TYPE_NAME)
+            }
+        }
+
+        impl From<$type> for Value {
+            fn from(v: $type) -> Self {
+                Value::$variant(v)
+            }
+        }
+    };
+
+    (@$other:ident($binding:ident)) => { Value::$other(_) };
+    (@$other:ident) => { Value::$other };
+}
+
+primitive! { bool: "boolean", Bool }
+primitive! { i64: "integer", Int }
+primitive! { f64: "float", Float, Int(v) => v as f64 }
+primitive! { Length: "length", Length }
+primitive! { Angle: "angle", Angle }
+primitive! { Ratio: "ratio", Ratio }
+primitive! { Rel<Length>:  "relative length",
+    Relative,
+    Length(v) => v.into(),
+    Ratio(v) => v.into()
+}
+primitive! { Fr: "fraction", Fraction }
+primitive! { Color: "color", Color }
+primitive! { Symbol: "symbol", Symbol }
+primitive! {
+    Str: "string",
+    Str,
+    Symbol(symbol) => symbol.get().into()
+}
+primitive! { Label: "label", Label }
+primitive! { Content: "content",
+    Content,
+    None => Content::empty(),
+    Symbol(v) => item!(text)(v.get().into()),
+    Str(v) => item!(text)(v.into())
+}
+primitive! { Array: "array", Array }
+primitive! { Dict: "dictionary", Dict }
+primitive! { Func: "function", Func }
+primitive! { Module: "module", Module }
+primitive! { Args: "arguments", Args }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::eval::{array, dict};
+
+    #[track_caller]
+    fn test(value: impl Into<Value>, exp: &str) {
+        assert_eq!(format!("{:?}", value.into()), exp);
+    }
+
+    #[test]
+    fn test_value_debug() {
+        // Primitives.
+        test(Value::None, "none");
+        test(false, "false");
+        test(12i64, "12");
+        test(3.14, "3.14");
+        test(Abs::pt(5.5), "5.5pt");
+        test(Angle::deg(90.0), "90deg");
+        test(Ratio::one() / 2.0, "50%");
+        test(Ratio::new(0.3) + Length::from(Abs::cm(2.0)), "30% + 56.69pt");
+        test(Fr::one() * 7.55, "7.55fr");
+        test(Color::Rgba(RgbaColor::new(1, 1, 1, 0xff)), "rgb(\"#010101\")");
+
+        // Collections.
+        test("hello", r#""hello""#);
+        test("\n", r#""\n""#);
+        test("\\", r#""\\""#);
+        test("\"", r#""\"""#);
+        test(array![], "()");
+        test(array![Value::None], "(none,)");
+        test(array![1, 2], "(1, 2)");
+        test(dict![], "(:)");
+        test(dict!["one" => 1], "(one: 1)");
+        test(dict!["two" => false, "one" => 1], "(one: 1, two: false)");
+    }
+}