Remove captured expression 🗑️

src/eval/capture.rs

@@ -3,17 +3,27 @@ use std::rc::Rc;
 use super::*;
 use crate::syntax::visit::*;
 
-/// A visitor that replaces all captured variables with their values.
+/// A visitor that captures variable slots.
 #[derive(Debug)]
 pub struct CapturesVisitor<'a> {
     external: &'a Scopes<'a>,
     internal: Scopes<'a>,
+    captures: Scope,
 }
 
 impl<'a> CapturesVisitor<'a> {
     /// Create a new visitor for the given external scopes.
     pub fn new(external: &'a Scopes) -> Self {
-        Self { external, internal: Scopes::default() }
+        Self {
+            external,
+            internal: Scopes::default(),
+            captures: Scope::new(),
+        }
+    }
+
+    /// Return the scope of capture variables.
+    pub fn finish(self) -> Scope {
+        self.captures
     }
 
     /// Define an internal variable.
@@ -23,14 +33,14 @@ impl<'a> CapturesVisitor<'a> {
 }
 
 impl<'ast> Visit<'ast> for CapturesVisitor<'_> {
-    fn visit_expr(&mut self, item: &'ast mut Expr) {
+    fn visit_expr(&mut self, item: &'ast Expr) {
         match item {
             Expr::Ident(ident) => {
                 // Find out whether the identifier is not locally defined, but
                 // captured, and if so, replace it with its value.
                 if self.internal.get(ident).is_none() {
-                    if let Some(value) = self.external.get(ident) {
+                    if let Some(slot) = self.external.get(ident) {
-                        *item = Expr::Captured(Rc::clone(&value));
+                        self.captures.def_slot(ident.as_str(), Rc::clone(slot));
                     }
                 }
             }
@@ -38,7 +48,7 @@ impl<'ast> Visit<'ast> for CapturesVisitor<'_> {
         }
     }
 
-    fn visit_block(&mut self, item: &'ast mut ExprBlock) {
+    fn visit_block(&mut self, item: &'ast ExprBlock) {
         // Blocks create a scope except if directly in a template.
         if item.scopes {
             self.internal.push();
@@ -49,20 +59,20 @@ impl<'ast> Visit<'ast> for CapturesVisitor<'_> {
         }
     }
 
-    fn visit_template(&mut self, item: &'ast mut ExprTemplate) {
+    fn visit_template(&mut self, item: &'ast ExprTemplate) {
         // Templates always create a scope.
         self.internal.push();
         visit_template(self, item);
         self.internal.pop();
     }
 
-    fn visit_let(&mut self, item: &'ast mut ExprLet) {
+    fn visit_let(&mut self, item: &'ast ExprLet) {
         self.define(&item.pat.v);
         visit_let(self, item);
     }
 
-    fn visit_for(&mut self, item: &'ast mut ExprFor) {
+    fn visit_for(&mut self, item: &'ast ExprFor) {
-        match &mut item.pat.v {
+        match &item.pat.v {
             ForPattern::Value(value) => self.define(value),
             ForPattern::KeyValue(key, value) => {
                 self.define(key);

src/eval/mod.rs

@@ -194,7 +194,6 @@ impl Eval for Spanned<&Expr> {
             Expr::Let(v) => v.with_span(self.span).eval(ctx),
             Expr::If(v) => v.with_span(self.span).eval(ctx),
             Expr::For(v) => v.with_span(self.span).eval(ctx),
-            Expr::Captured(v) => v.borrow().clone(),
         }
     }
 }
@@ -344,21 +343,17 @@ impl Spanned<&ExprBinary> {
         let rhs = self.v.rhs.eval(ctx);
         let span = self.v.lhs.span;
 
-        let slot = match &self.v.lhs.v {
+        let slot = if let Expr::Ident(id) = &self.v.lhs.v {
-            Expr::Ident(id) => match ctx.scopes.get(id) {
+            match ctx.scopes.get(id) {
                 Some(slot) => slot,
                 None => {
                     ctx.diag(error!(span, "unknown variable"));
                     return Value::Error;
                 }
-            },
-
-            Expr::Captured(slot) => slot,
-
-            _ => {
-                ctx.diag(error!(span, "cannot assign to this expression"));
-                return Value::Error;
             }
+        } else {
+            ctx.diag(error!(span, "cannot assign to this expression"));
+            return Value::Error;
         };
 
         let (constant, err, value) = if let Ok(mut inner) = slot.try_borrow_mut() {

src/eval/scope.rs

@@ -86,6 +86,11 @@ impl Scope {
         self.values.insert(var.into(), Rc::new(RefCell::new(value.into())));
     }
 
+    /// Define a variable with a slot.
+    pub fn def_slot(&mut self, var: impl Into<String>, slot: Slot) {
+        self.values.insert(var.into(), slot);
+    }
+
     /// Look up the value of a variable.
     pub fn get(&self, var: &str) -> Option<&Slot> {
         self.values.get(var)

src/syntax/expr.rs

@@ -1,6 +1,5 @@
 use super::*;
 use crate::color::RgbaColor;
-use crate::eval::Slot;
 use crate::geom::{AngularUnit, LengthUnit};
 
 /// An expression.
@@ -51,11 +50,6 @@ pub enum Expr {
     If(ExprIf),
     /// A for expression: `#for x #in y { z }`.
     For(ExprFor),
-    /// A captured variable slot.
-    ///
-    /// This node is never created by parsing. It only results from an in-place
-    /// transformation of an identifier to a captured variable.
-    Captured(Slot),
 }
 
 impl Pretty for Expr {
@@ -92,7 +86,6 @@ impl Pretty for Expr {
             Self::Let(v) => v.pretty(p),
             Self::If(v) => v.pretty(p),
             Self::For(v) => v.pretty(p),
-            Self::Captured(v) => v.borrow().pretty(p),
         }
     }
 }

src/syntax/visit.rs

@@ -3,17 +3,17 @@
 use super::*;
 
 macro_rules! visit {
-    ($(fn $name:ident($v:ident, $item:ident: &mut $ty:ty) $body:block)*) => {
+    ($(fn $name:ident($v:ident, $item:ident: &$ty:ty) $body:block)*) => {
         /// Traverses the syntax tree.
         pub trait Visit<'ast> {
-            $(fn $name(&mut self, $item: &'ast mut $ty) {
+            $(fn $name(&mut self, $item: &'ast $ty) {
                 $name(self, $item);
             })*
         }
 
         $(visit! {
             @concat!("Walk a node of type [`", stringify!($ty), "`]."),
-            pub fn $name<'ast, V>($v: &mut V, $item: &'ast mut $ty)
+            pub fn $name<'ast, V>($v: &mut V, $item: &'ast $ty)
             where
                 V: Visit<'ast> + ?Sized
             $body
@@ -27,13 +27,13 @@ macro_rules! visit {
 }
 
 visit! {
-    fn visit_tree(v, item: &mut Tree) {
+    fn visit_tree(v, item: &Tree) {
         for node in item {
-            v.visit_node(&mut node.v);
+            v.visit_node(&node.v);
         }
     }
 
-    fn visit_node(v, item: &mut Node) {
+    fn visit_node(v, item: &Node) {
         match item {
             Node::Strong => {}
             Node::Emph => {}
@@ -41,13 +41,13 @@ visit! {
             Node::Linebreak => {}
             Node::Parbreak => {}
             Node::Text(_) => {}
-            Node::Heading(n) => v.visit_tree(&mut n.contents),
+            Node::Heading(n) => v.visit_tree(&n.contents),
             Node::Raw(_) => {}
             Node::Expr(expr) => v.visit_expr(expr),
         }
     }
 
-    fn visit_expr(v, item: &mut Expr) {
+    fn visit_expr(v, item: &Expr) {
         match item {
             Expr::None => {}
             Expr::Ident(_) => {}
@@ -70,79 +70,78 @@ visit! {
             Expr::Let(e) => v.visit_let(e),
             Expr::If(e) => v.visit_if(e),
             Expr::For(e) => v.visit_for(e),
-            Expr::Captured(_) => {}
         }
     }
 
-    fn visit_array(v, item: &mut ExprArray) {
+    fn visit_array(v, item: &ExprArray) {
         for expr in item {
-            v.visit_expr(&mut expr.v);
+            v.visit_expr(&expr.v);
         }
     }
 
-    fn visit_dict(v, item: &mut ExprDict) {
+    fn visit_dict(v, item: &ExprDict) {
         for named in item {
-            v.visit_expr(&mut named.expr.v);
+            v.visit_expr(&named.expr.v);
         }
     }
 
-    fn visit_template(v, item: &mut ExprTemplate) {
+    fn visit_template(v, item: &ExprTemplate) {
         v.visit_tree(item);
     }
 
-    fn visit_group(v, item: &mut ExprGroup) {
+    fn visit_group(v, item: &ExprGroup) {
-        v.visit_expr(&mut item.v);
+        v.visit_expr(&item.v);
     }
 
-    fn visit_block(v, item: &mut ExprBlock) {
+    fn visit_block(v, item: &ExprBlock) {
-        for expr in &mut item.exprs {
+        for expr in &item.exprs {
-            v.visit_expr(&mut expr.v);
+            v.visit_expr(&expr.v);
         }
     }
 
-    fn visit_binary(v, item: &mut ExprBinary) {
+    fn visit_binary(v, item: &ExprBinary) {
-        v.visit_expr(&mut item.lhs.v);
+        v.visit_expr(&item.lhs.v);
-        v.visit_expr(&mut item.rhs.v);
+        v.visit_expr(&item.rhs.v);
     }
 
-    fn visit_unary(v, item: &mut ExprUnary) {
+    fn visit_unary(v, item: &ExprUnary) {
-        v.visit_expr(&mut item.expr.v);
+        v.visit_expr(&item.expr.v);
     }
 
-    fn visit_call(v, item: &mut ExprCall) {
+    fn visit_call(v, item: &ExprCall) {
-        v.visit_expr(&mut item.callee.v);
+        v.visit_expr(&item.callee.v);
-        v.visit_args(&mut item.args.v);
+        v.visit_args(&item.args.v);
     }
 
-    fn visit_args(v, item: &mut ExprArgs) {
+    fn visit_args(v, item: &ExprArgs) {
         for arg in item {
             v.visit_arg(arg);
         }
     }
 
-    fn visit_arg(v, item: &mut Argument) {
+    fn visit_arg(v, item: &Argument) {
         match item {
-            Argument::Pos(expr) => v.visit_expr(&mut expr.v),
+            Argument::Pos(expr) => v.visit_expr(&expr.v),
-            Argument::Named(named) => v.visit_expr(&mut named.expr.v),
+            Argument::Named(named) => v.visit_expr(&named.expr.v),
         }
     }
 
-    fn visit_let(v, item: &mut ExprLet) {
+    fn visit_let(v, item: &ExprLet) {
-        if let Some(init) = &mut item.init {
+        if let Some(init) = &item.init {
-            v.visit_expr(&mut init.v);
+            v.visit_expr(&init.v);
         }
     }
 
-    fn visit_if(v, item: &mut ExprIf) {
+    fn visit_if(v, item: &ExprIf) {
-        v.visit_expr(&mut item.condition.v);
+        v.visit_expr(&item.condition.v);
-        v.visit_expr(&mut item.if_body.v);
+        v.visit_expr(&item.if_body.v);
-        if let Some(body) = &mut item.else_body {
+        if let Some(body) = &item.else_body {
-            v.visit_expr(&mut body.v);
+            v.visit_expr(&body.v);
         }
     }
 
-    fn visit_for(v, item: &mut ExprFor) {
+    fn visit_for(v, item: &ExprFor) {
-        v.visit_expr(&mut item.iter.v);
+        v.visit_expr(&item.iter.v);
-        v.visit_expr(&mut item.body.v);
+        v.visit_expr(&item.body.v);
     }
 }