Expression evaluation with Eval trait 🧮

5 files changed, 295 insertions, 246 deletions

diff --git a/Cargo.toml b/Cargo.toml
index d1f7f946..a9d8011d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -22,6 +22,7 @@ opt-level = 2
 lto = true
 
 [dependencies]
+async-trait = "0.1"
 fontdock = { path = "../fontdock", default-features = false }
 kurbo = "0.6.3"
 tide = { path = "../tide" }
diff --git a/src/eval/mod.rs b/src/eval/mod.rs
index d21fbc7f..dc35ce71 100644
--- a/src/eval/mod.rs
+++ b/src/eval/mod.rs
@@ -9,3 +9,288 @@ pub use dict::*;
 pub use scope::*;
 pub use state::*;
 pub use value::*;
+
+use async_trait::async_trait;
+
+use crate::layout::LayoutContext;
+use crate::syntax::*;
+
+/// Evaluate an syntactic item into an output value.
+///
+/// _Note_: Evaluation is not necessarily pure, it may change the active state.
+#[async_trait(?Send)]
+pub trait Eval {
+    /// The output of evaluating the item.
+    type Output;
+
+    /// Evaluate the item to the output value.
+    async fn eval(&self, ctx: &mut LayoutContext) -> Self::Output;
+}
+
+#[async_trait(?Send)]
+impl Eval for Expr {
+    type Output = Value;
+
+    async fn eval(&self, ctx: &mut LayoutContext) -> Self::Output {
+        match self {
+            Self::Lit(lit) => lit.eval(ctx).await,
+            Self::Call(call) => call.eval(ctx).await,
+            Self::Unary(unary) => unary.eval(ctx).await,
+            Self::Binary(binary) => binary.eval(ctx).await,
+        }
+    }
+}
+
+#[async_trait(?Send)]
+impl Eval for Lit {
+    type Output = Value;
+
+    async fn eval(&self, ctx: &mut LayoutContext) -> Self::Output {
+        match *self {
+            Lit::Ident(ref v) => Value::Ident(v.clone()),
+            Lit::Bool(v) => Value::Bool(v),
+            Lit::Int(v) => Value::Int(v),
+            Lit::Float(v) => Value::Float(v),
+            Lit::Length(v) => Value::Length(v.as_raw()),
+            Lit::Percent(v) => Value::Relative(v / 100.0),
+            Lit::Color(v) => Value::Color(v),
+            Lit::Str(ref v) => Value::Str(v.clone()),
+            Lit::Dict(ref v) => Value::Dict(v.eval(ctx).await),
+            Lit::Content(ref v) => Value::Content(v.clone()),
+        }
+    }
+}
+#[async_trait(?Send)]
+impl Eval for LitDict {
+    type Output = ValueDict;
+
+    async fn eval(&self, ctx: &mut LayoutContext) -> Self::Output {
+        let mut dict = ValueDict::new();
+
+        for entry in &self.0 {
+            let val = entry.expr.v.eval(ctx).await;
+            let spanned = val.span_with(entry.expr.span);
+            if let Some(key) = &entry.key {
+                dict.insert(&key.v, SpannedEntry::new(key.span, spanned));
+            } else {
+                dict.push(SpannedEntry::value(spanned));
+            }
+        }
+
+        dict
+    }
+}
+
+#[async_trait(?Send)]
+impl Eval for ExprCall {
+    type Output = Value;
+
+    async fn eval(&self, ctx: &mut LayoutContext) -> Self::Output {
+        let name = &self.name.v;
+        let span = self.name.span;
+        let args = self.args.eval(ctx).await;
+
+        if let Some(func) = ctx.state.scope.func(name) {
+            ctx.f.decorations.push(Decoration::Resolved.span_with(span));
+            (func.clone())(args, ctx).await
+        } else {
+            if !name.is_empty() {
+                error!(@ctx.f, span, "unknown function");
+                ctx.f.decorations.push(Decoration::Unresolved.span_with(span));
+            }
+            Value::Dict(args)
+        }
+    }
+}
+
+#[async_trait(?Send)]
+impl Eval for ExprUnary {
+    type Output = Value;
+
+    async fn eval(&self, ctx: &mut LayoutContext) -> Self::Output {
+        use Value::*;
+
+        let value = self.expr.v.eval(ctx).await;
+        if value == Error {
+            return Error;
+        }
+
+        let span = self.op.span.join(self.expr.span);
+        match self.op.v {
+            UnOp::Neg => neg(ctx, span, value),
+        }
+    }
+}
+
+#[async_trait(?Send)]
+impl Eval for ExprBinary {
+    type Output = Value;
+
+    async fn eval(&self, ctx: &mut LayoutContext) -> Self::Output {
+        let lhs = self.lhs.v.eval(ctx).await;
+        let rhs = self.rhs.v.eval(ctx).await;
+
+        if lhs == Value::Error || rhs == Value::Error {
+            return Value::Error;
+        }
+
+        let span = self.lhs.span.join(self.rhs.span);
+        match self.op.v {
+            BinOp::Add => add(ctx, span, lhs, rhs),
+            BinOp::Sub => sub(ctx, span, lhs, rhs),
+            BinOp::Mul => mul(ctx, span, lhs, rhs),
+            BinOp::Div => div(ctx, span, lhs, rhs),
+        }
+    }
+}
+
+/// Compute the negation of a value.
+fn neg(ctx: &mut LayoutContext, span: Span, value: Value) -> Value {
+    use Value::*;
+    match value {
+        Int(v) => Int(-v),
+        Float(v) => Float(-v),
+        Length(v) => Length(-v),
+        Relative(v) => Relative(-v),
+        Linear(v) => Linear(-v),
+        v => {
+            error!(@ctx.f, span, "cannot negate {}", v.ty());
+            Value::Error
+        }
+    }
+}
+
+/// Compute the sum of two values.
+fn add(ctx: &mut LayoutContext, span: Span, lhs: Value, rhs: Value) -> Value {
+    use crate::geom::Linear as Lin;
+    use Value::*;
+    match (lhs, rhs) {
+        // Numbers to themselves.
+        (Int(a), Int(b)) => Int(a + b),
+        (Int(a), Float(b)) => Float(a as f64 + b),
+        (Float(a), Int(b)) => Float(a + b as f64),
+        (Float(a), Float(b)) => Float(a + b),
+
+        // Lengths, relatives and linears to themselves.
+        (Length(a), Length(b)) => Length(a + b),
+        (Length(a), Relative(b)) => Linear(Lin::abs(a) + Lin::rel(b)),
+        (Length(a), Linear(b)) => Linear(Lin::abs(a) + b),
+
+        (Relative(a), Length(b)) => Linear(Lin::rel(a) + Lin::abs(b)),
+        (Relative(a), Relative(b)) => Relative(a + b),
+        (Relative(a), Linear(b)) => Linear(Lin::rel(a) + b),
+
+        (Linear(a), Length(b)) => Linear(a + Lin::abs(b)),
+        (Linear(a), Relative(b)) => Linear(a + Lin::rel(b)),
+        (Linear(a), Linear(b)) => Linear(a + b),
+
+        // Complex data types to themselves.
+        (Str(a), Str(b)) => Str(a + &b),
+        (Dict(a), Dict(b)) => Dict(concat(a, b)),
+        (Content(a), Content(b)) => Content(concat(a, b)),
+        (Commands(a), Commands(b)) => Commands(concat(a, b)),
+
+        (a, b) => {
+            error!(@ctx.f, span, "cannot add {} and {}", a.ty(), b.ty());
+            Value::Error
+        }
+    }
+}
+
+/// Compute the difference of two values.
+fn sub(ctx: &mut LayoutContext, span: Span, lhs: Value, rhs: Value) -> Value {
+    use crate::geom::Linear as Lin;
+    use Value::*;
+    match (lhs, rhs) {
+        // Numbers from themselves.
+        (Int(a), Int(b)) => Int(a - b),
+        (Int(a), Float(b)) => Float(a as f64 - b),
+        (Float(a), Int(b)) => Float(a - b as f64),
+        (Float(a), Float(b)) => Float(a - b),
+
+        // Lengths, relatives and linears from themselves.
+        (Length(a), Length(b)) => Length(a - b),
+        (Length(a), Relative(b)) => Linear(Lin::abs(a) - Lin::rel(b)),
+        (Length(a), Linear(b)) => Linear(Lin::abs(a) - b),
+        (Relative(a), Length(b)) => Linear(Lin::rel(a) - Lin::abs(b)),
+        (Relative(a), Relative(b)) => Relative(a - b),
+        (Relative(a), Linear(b)) => Linear(Lin::rel(a) - b),
+        (Linear(a), Length(b)) => Linear(a - Lin::abs(b)),
+        (Linear(a), Relative(b)) => Linear(a - Lin::rel(b)),
+        (Linear(a), Linear(b)) => Linear(a - b),
+
+        (a, b) => {
+            error!(@ctx.f, span, "cannot subtract {1} from {0}", a.ty(), b.ty());
+            Value::Error
+        }
+    }
+}
+
+/// Compute the product of two values.
+fn mul(ctx: &mut LayoutContext, span: Span, lhs: Value, rhs: Value) -> Value {
+    use Value::*;
+    match (lhs, rhs) {
+        // Numbers with themselves.
+        (Int(a), Int(b)) => Int(a * b),
+        (Int(a), Float(b)) => Float(a as f64 * b),
+        (Float(a), Int(b)) => Float(a * b as f64),
+        (Float(a), Float(b)) => Float(a * b),
+
+        // Lengths, relatives and linears with numbers.
+        (Length(a), Int(b)) => Length(a * b as f64),
+        (Length(a), Float(b)) => Length(a * b),
+        (Int(a), Length(b)) => Length(a as f64 * b),
+        (Float(a), Length(b)) => Length(a * b),
+        (Relative(a), Int(b)) => Relative(a * b as f64),
+        (Relative(a), Float(b)) => Relative(a * b),
+        (Int(a), Relative(b)) => Relative(a as f64 * b),
+        (Float(a), Relative(b)) => Relative(a * b),
+        (Linear(a), Int(b)) => Linear(a * b as f64),
+        (Linear(a), Float(b)) => Linear(a * b),
+        (Int(a), Linear(b)) => Linear(a as f64 * b),
+        (Float(a), Linear(b)) => Linear(a * b),
+
+        // Integers with strings.
+        (Int(a), Str(b)) => Str(b.repeat(a.max(0) as usize)),
+        (Str(a), Int(b)) => Str(a.repeat(b.max(0) as usize)),
+
+        (a, b) => {
+            error!(@ctx.f, span, "cannot multiply {} with {}", a.ty(), b.ty());
+            Value::Error
+        }
+    }
+}
+
+/// Compute the quotient of two values.
+fn div(ctx: &mut LayoutContext, span: Span, lhs: Value, rhs: Value) -> Value {
+    use Value::*;
+    match (lhs, rhs) {
+        // Numbers by themselves.
+        (Int(a), Int(b)) => Float(a as f64 / b as f64),
+        (Int(a), Float(b)) => Float(a as f64 / b),
+        (Float(a), Int(b)) => Float(a / b as f64),
+        (Float(a), Float(b)) => Float(a / b),
+
+        // Lengths by numbers.
+        (Length(a), Int(b)) => Length(a / b as f64),
+        (Length(a), Float(b)) => Length(a / b),
+        (Relative(a), Int(b)) => Relative(a / b as f64),
+        (Relative(a), Float(b)) => Relative(a / b),
+        (Linear(a), Int(b)) => Linear(a / b as f64),
+        (Linear(a), Float(b)) => Linear(a / b),
+
+        (a, b) => {
+            error!(@ctx.f, span, "cannot divide {} by {}", a.ty(), b.ty());
+            Value::Error
+        }
+    }
+}
+
+/// Concatenate two collections.
+fn concat<T, A>(mut a: T, b: T) -> T
+where
+    T: Extend<A> + IntoIterator<Item = A>,
+{
+    a.extend(b);
+    a
+}
diff --git a/src/layout/tree.rs b/src/layout/tree.rs
index 791bf14b..4dbf716e 100644
--- a/src/layout/tree.rs
+++ b/src/layout/tree.rs
@@ -1,6 +1,7 @@
 //! Layouting of syntax trees.
 
 use super::*;
+use crate::eval::Eval;
 use crate::shaping;
 use crate::syntax::{
     Decoration, Expr, NodeHeading, NodeRaw, Span, SpanWith, Spanned, SynNode, SynTree,
diff --git a/src/syntax/ast/expr.rs b/src/syntax/ast/expr.rs
index 718b0568..4f440d33 100644
--- a/src/syntax/ast/expr.rs
+++ b/src/syntax/ast/expr.rs
@@ -1,9 +1,6 @@
 //! Expressions.
 
 use super::*;
-use crate::eval::Value;
-use crate::layout::LayoutContext;
-use crate::DynFuture;
 
 /// An expression.
 #[derive(Debug, Clone, PartialEq)]
@@ -18,20 +15,6 @@ pub enum Expr {
     Binary(ExprBinary),
 }
 
-impl Expr {
-    /// Evaluate the expression to a value.
-    pub fn eval<'a>(&'a self, ctx: &'a mut LayoutContext) -> DynFuture<'a, Value> {
-        Box::pin(async move {
-            match self {
-                Self::Lit(lit) => lit.eval(ctx).await,
-                Self::Call(call) => call.eval(ctx).await,
-                Self::Unary(unary) => unary.eval(ctx).await,
-                Self::Binary(binary) => binary.eval(ctx).await,
-            }
-        })
-    }
-}
-
 /// An invocation of a function: `[foo: ...]`, `foo(...)`.
 #[derive(Debug, Clone, PartialEq)]
 pub struct ExprCall {
@@ -41,26 +24,6 @@ pub struct ExprCall {
     pub args: LitDict,
 }
 
-impl ExprCall {
-    /// Evaluate the call expression to a value.
-    pub async fn eval(&self, ctx: &mut LayoutContext) -> Value {
-        let name = &self.name.v;
-        let span = self.name.span;
-        let args = self.args.eval(ctx).await;
-
-        if let Some(func) = ctx.state.scope.func(name) {
-            ctx.f.decorations.push(Decoration::Resolved.span_with(span));
-            (func.clone())(args, ctx).await
-        } else {
-            if !name.is_empty() {
-                error!(@ctx.f, span, "unknown function");
-                ctx.f.decorations.push(Decoration::Unresolved.span_with(span));
-            }
-            Value::Dict(args)
-        }
-    }
-}
-
 /// A unary operation: `-x`.
 #[derive(Debug, Clone, PartialEq)]
 pub struct ExprUnary {
@@ -70,33 +33,6 @@ pub struct ExprUnary {
     pub expr: Spanned<Box<Expr>>,
 }
 
-impl ExprUnary {
-    /// Evaluate the expression to a value.
-    pub async fn eval(&self, ctx: &mut LayoutContext) -> Value {
-        use Value::*;
-
-        let value = self.expr.v.eval(ctx).await;
-        if value == Error {
-            return Error;
-        }
-
-        let span = self.op.span.join(self.expr.span);
-        match self.op.v {
-            UnOp::Neg => match value {
-                Int(v) => Int(-v),
-                Float(v) => Float(-v),
-                Length(v) => Length(-v),
-                Relative(v) => Relative(-v),
-                Linear(v) => Linear(-v),
-                v => {
-                    error!(@ctx.f, span, "cannot negate {}", v.ty());
-                    Value::Error
-                }
-            },
-        }
-    }
-}
-
 /// A unary operator.
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub enum UnOp {
@@ -115,141 +51,6 @@ pub struct ExprBinary {
     pub rhs: Spanned<Box<Expr>>,
 }
 
-impl ExprBinary {
-    /// Evaluate the expression to a value.
-    pub async fn eval(&self, ctx: &mut LayoutContext) -> Value {
-        use crate::geom::Linear as Lin;
-        use Value::*;
-
-        let lhs = self.lhs.v.eval(ctx).await;
-        let rhs = self.rhs.v.eval(ctx).await;
-
-        if lhs == Error || rhs == Error {
-            return Error;
-        }
-
-        let span = self.lhs.span.join(self.rhs.span);
-        match self.op.v {
-            BinOp::Add => match (lhs, rhs) {
-                // Numbers to themselves.
-                (Int(a), Int(b)) => Int(a + b),
-                (Int(a), Float(b)) => Float(a as f64 + b),
-                (Float(a), Int(b)) => Float(a + b as f64),
-                (Float(a), Float(b)) => Float(a + b),
-
-                // Lengths, relatives and linears to themselves.
-                (Length(a), Length(b)) => Length(a + b),
-                (Length(a), Relative(b)) => Linear(Lin::abs(a) + Lin::rel(b)),
-                (Length(a), Linear(b)) => Linear(Lin::abs(a) + b),
-
-                (Relative(a), Length(b)) => Linear(Lin::rel(a) + Lin::abs(b)),
-                (Relative(a), Relative(b)) => Relative(a + b),
-                (Relative(a), Linear(b)) => Linear(Lin::rel(a) + b),
-
-                (Linear(a), Length(b)) => Linear(a + Lin::abs(b)),
-                (Linear(a), Relative(b)) => Linear(a + Lin::rel(b)),
-                (Linear(a), Linear(b)) => Linear(a + b),
-
-                // Complex data types to themselves.
-                (Str(a), Str(b)) => Str(a + &b),
-                (Dict(a), Dict(b)) => Dict(concat(a, b)),
-                (Content(a), Content(b)) => Content(concat(a, b)),
-                (Commands(a), Commands(b)) => Commands(concat(a, b)),
-
-                (a, b) => {
-                    error!(@ctx.f, span, "cannot add {} and {}", a.ty(), b.ty());
-                    Value::Error
-                }
-            },
-
-            BinOp::Sub => match (lhs, rhs) {
-                // Numbers from themselves.
-                (Int(a), Int(b)) => Int(a - b),
-                (Int(a), Float(b)) => Float(a as f64 - b),
-                (Float(a), Int(b)) => Float(a - b as f64),
-                (Float(a), Float(b)) => Float(a - b),
-
-                // Lengths, relatives and linears from themselves.
-                (Length(a), Length(b)) => Length(a - b),
-                (Length(a), Relative(b)) => Linear(Lin::abs(a) - Lin::rel(b)),
-                (Length(a), Linear(b)) => Linear(Lin::abs(a) - b),
-                (Relative(a), Length(b)) => Linear(Lin::rel(a) - Lin::abs(b)),
-                (Relative(a), Relative(b)) => Relative(a - b),
-                (Relative(a), Linear(b)) => Linear(Lin::rel(a) - b),
-                (Linear(a), Length(b)) => Linear(a - Lin::abs(b)),
-                (Linear(a), Relative(b)) => Linear(a - Lin::rel(b)),
-                (Linear(a), Linear(b)) => Linear(a - b),
-
-                (a, b) => {
-                    error!(@ctx.f, span, "cannot subtract {1} from {0}", a.ty(), b.ty());
-                    Value::Error
-                }
-            },
-
-            BinOp::Mul => match (lhs, rhs) {
-                // Numbers with themselves.
-                (Int(a), Int(b)) => Int(a * b),
-                (Int(a), Float(b)) => Float(a as f64 * b),
-                (Float(a), Int(b)) => Float(a * b as f64),
-                (Float(a), Float(b)) => Float(a * b),
-
-                // Lengths, relatives and linears with numbers.
-                (Length(a), Int(b)) => Length(a * b as f64),
-                (Length(a), Float(b)) => Length(a * b),
-                (Int(a), Length(b)) => Length(a as f64 * b),
-                (Float(a), Length(b)) => Length(a * b),
-                (Relative(a), Int(b)) => Relative(a * b as f64),
-                (Relative(a), Float(b)) => Relative(a * b),
-                (Int(a), Relative(b)) => Relative(a as f64 * b),
-                (Float(a), Relative(b)) => Relative(a * b),
-                (Linear(a), Int(b)) => Linear(a * b as f64),
-                (Linear(a), Float(b)) => Linear(a * b),
-                (Int(a), Linear(b)) => Linear(a as f64 * b),
-                (Float(a), Linear(b)) => Linear(a * b),
-
-                // Integers with strings.
-                (Int(a), Str(b)) => Str(b.repeat(a.max(0) as usize)),
-                (Str(a), Int(b)) => Str(a.repeat(b.max(0) as usize)),
-
-                (a, b) => {
-                    error!(@ctx.f, span, "cannot multiply {} with {}", a.ty(), b.ty());
-                    Value::Error
-                }
-            },
-
-            BinOp::Div => match (lhs, rhs) {
-                // Numbers by themselves.
-                (Int(a), Int(b)) => Float(a as f64 / b as f64),
-                (Int(a), Float(b)) => Float(a as f64 / b),
-                (Float(a), Int(b)) => Float(a / b as f64),
-                (Float(a), Float(b)) => Float(a / b),
-
-                // Lengths by numbers.
-                (Length(a), Int(b)) => Length(a / b as f64),
-                (Length(a), Float(b)) => Length(a / b),
-                (Relative(a), Int(b)) => Relative(a / b as f64),
-                (Relative(a), Float(b)) => Relative(a / b),
-                (Linear(a), Int(b)) => Linear(a / b as f64),
-                (Linear(a), Float(b)) => Linear(a / b),
-
-                (a, b) => {
-                    error!(@ctx.f, span, "cannot divide {} by {}", a.ty(), b.ty());
-                    Value::Error
-                }
-            },
-        }
-    }
-}
-
-/// Concatenate two collections.
-fn concat<T, A>(mut a: T, b: T) -> T
-where
-    T: Extend<A> + IntoIterator<Item = A>,
-{
-    a.extend(b);
-    a
-}
-
 /// A binary operator.
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub enum BinOp {
diff --git a/src/syntax/ast/lit.rs b/src/syntax/ast/lit.rs
index 414d5490..31566e89 100644
--- a/src/syntax/ast/lit.rs
+++ b/src/syntax/ast/lit.rs
@@ -2,10 +2,8 @@
 
 use super::*;
 use crate::color::RgbaColor;
-use crate::eval::{DictKey, SpannedEntry, Value, ValueDict};
-use crate::layout::LayoutContext;
+use crate::eval::DictKey;
 use crate::length::Length;
-use crate::DynFuture;
 
 /// A literal.
 #[derive(Debug, Clone, PartialEq)]
@@ -37,54 +35,10 @@ pub enum Lit {
     Content(SynTree),
 }
 
-impl Lit {
-    /// Evaluate the dictionary literal to a dictionary value.
-    pub async fn eval(&self, ctx: &mut LayoutContext) -> Value {
-        match *self {
-            Lit::Ident(ref v) => Value::Ident(v.clone()),
-            Lit::Bool(v) => Value::Bool(v),
-            Lit::Int(v) => Value::Int(v),
-            Lit::Float(v) => Value::Float(v),
-            Lit::Length(v) => Value::Length(v.as_raw()),
-            Lit::Percent(v) => Value::Relative(v / 100.0),
-            Lit::Color(v) => Value::Color(v),
-            Lit::Str(ref v) => Value::Str(v.clone()),
-            Lit::Dict(ref v) => Value::Dict(v.eval(ctx).await),
-            Lit::Content(ref v) => Value::Content(v.clone()),
-        }
-    }
-}
-
 /// A dictionary literal: `(false, 12cm, greeting = "hi")`.
 #[derive(Debug, Clone, PartialEq)]
 pub struct LitDict(pub Vec<LitDictEntry>);
 
-impl LitDict {
-    /// Create an empty dict literal.
-    pub fn new() -> Self {
-        Self(vec![])
-    }
-
-    /// Evaluate the dictionary literal to a dictionary value.
-    pub fn eval<'a>(&'a self, ctx: &'a mut LayoutContext) -> DynFuture<'a, ValueDict> {
-        Box::pin(async move {
-            let mut dict = ValueDict::new();
-
-            for entry in &self.0 {
-                let val = entry.expr.v.eval(ctx).await;
-                let spanned = val.span_with(entry.expr.span);
-                if let Some(key) = &entry.key {
-                    dict.insert(&key.v, SpannedEntry::new(key.span, spanned));
-                } else {
-                    dict.push(SpannedEntry::value(spanned));
-                }
-            }
-
-            dict
-        })
-    }
-}
-
 /// An entry in a dictionary literal: `false` or `greeting = "hi"`.
 #[derive(Debug, Clone, PartialEq)]
 pub struct LitDictEntry {
@@ -93,3 +47,10 @@ pub struct LitDictEntry {
     /// The value of the entry: `"hi"`.
     pub expr: Spanned<Expr>,
 }
+
+impl LitDict {
+    /// Create an empty dict literal.
+    pub fn new() -> Self {
+        Self(vec![])
+    }
+}