feat: Allow macros to refer to symbols in scope at the expansion site

Fixes gluon-lang#895

README.md

@@ -60,17 +60,17 @@ factorial 10
 // * Only the following operators/functions are allowed: multiplication, division, addition, subtraction
 // * Division should use floating point or rational arithmetic, etc, to preserve remainders.
 // * Brackets are allowed, if using an infix expression evaluator.
-// * Forming multiple digit numbers from the supplied digits is disallowed. (So an answer of 12+12 - when given 1, 2, 2, and 1 - is wrong).
-// * The order of the digits, when given, does not have to be preserved.
+// * Forming multiple digit numbers from the supplied digits is disallowed. (So an answer of 12+12 when given 1, 2, 2, and 1 is wrong).
+// * The order of the digits when given does not have to be preserved.
 //
 //
 // ## Notes
 //
 //     The type of expression evaluator used is not mandated. An RPN evaluator is equally acceptable for example.
-//     The task is not for the program to generate the expression or test whether an expression is even possible.
+//     The task is not for the program to generate the expression, or test whether an expression is even possible.
 
 
-// The `import!` macro is used to load and refer to other modules.
+// The `import!` macro are used to load and refer to other modules.
 // It gets replaced by the value returned by evaluating that module (cached of course, so that
 // multiple `import!`s to the same module only evaluates the module once)
 let io @ { ? } = import! std.io
@@ -83,7 +83,7 @@ let list @ { List, ? } = import! std.list
 let random = import! std.random
 let string = import! std.string
 
-// Since imports in gluon return regular values we can load specific parts of a module using pattern matches.
+// Since imports in gluon returns regular values we can load specific parts of a module using pattern matches.
 let char @ { ? } = import! std.char
 
 let { (<>) } = import! std.semigroup

src/import.rs

@@ -25,7 +25,7 @@ use crate::base::{
     ast::{self, expr_to_path, Expr, Literal, SpannedExpr},
     filename_to_module, pos,
     source::FileId,
-    symbol::Symbol,
+    symbol::{Symbol, Symbols},
     types::ArcType,
 };
 
@@ -477,9 +477,10 @@ where
         }
     }
 
-    fn expand<'r, 'a: 'r, 'b: 'r, 'ast: 'r>(
+    fn expand<'r, 'a: 'r, 'b: 'r, 'c: 'r, 'ast: 'r>(
         &self,
         macros: &'b mut MacroExpander<'a>,
+        _symbols: &'c mut Symbols,
         _arena: &'b mut ast::OwnedArena<'ast, Symbol>,
         args: &'b mut [SpannedExpr<'ast, Symbol>],
     ) -> MacroFuture<'r, 'ast> {

src/lift_io.rs

@@ -22,9 +22,10 @@ use {
 pub(crate) struct LiftIo;
 
 impl Macro for LiftIo {
-    fn expand<'r, 'a: 'r, 'b: 'r, 'ast: 'r>(
+    fn expand<'r, 'a: 'r, 'b: 'r, 'c: 'r, 'ast: 'r>(
         &self,
         env: &'b mut MacroExpander<'a>,
+        _symbols: &'c mut Symbols,
         arena: &'b mut ast::OwnedArena<'ast, Symbol>,
         args: &'b mut [SpannedExpr<'ast, Symbol>],
     ) -> MacroFuture<'r, 'ast> {

vm/src/macros.rs

@@ -245,9 +245,13 @@ pub trait Macro: Trace + DowncastArc + Send + Sync {
         None
     }
 
-    fn expand<'r, 'a: 'r, 'b: 'r, 'ast: 'r>(
+    /// Creating a symbol in `symbols` will put it in the same scope as the code surrounding the
+    /// expansion. If you want to create a unique symbol then call `Symbol::from` or create a new
+    /// `Symbols` table
+    fn expand<'r, 'a: 'r, 'b: 'r, 'c: 'r, 'ast: 'r>(
         &self,
         env: &'b mut MacroExpander<'a>,
+        symbols: &'c mut Symbols,
         arena: &'b mut ast::OwnedArena<'ast, Symbol>,
         args: &'b mut [SpannedExpr<'ast, Symbol>],
     ) -> MacroFuture<'r, 'ast>;
@@ -283,13 +287,14 @@ where
         (**self).get_capability_impl(thread, arc_self, id)
     }
 
-    fn expand<'r, 'a: 'r, 'b: 'r, 'ast: 'r>(
+    fn expand<'r, 'a: 'r, 'b: 'r, 'c: 'r, 'ast: 'r>(
         &self,
         env: &'b mut MacroExpander<'a>,
+        symbols: &'c mut Symbols,
         arena: &'b mut ast::OwnedArena<'ast, Symbol>,
         args: &'b mut [SpannedExpr<'ast, Symbol>],
     ) -> MacroFuture<'r, 'ast> {
-        (**self).expand(env, arena, args)
+        (**self).expand(env, symbols, arena, args)
     }
 }
 
@@ -307,13 +312,14 @@ where
         (**self).get_capability_impl(thread, arc_self, id)
     }
 
-    fn expand<'r, 'a: 'r, 'b: 'r, 'ast: 'r>(
+    fn expand<'r, 'a: 'r, 'b: 'r, 'c: 'r, 'ast: 'r>(
         &self,
         env: &'b mut MacroExpander<'a>,
+        symbols: &'c mut Symbols,
         arena: &'b mut ast::OwnedArena<'ast, Symbol>,
         args: &'b mut [SpannedExpr<'ast, Symbol>],
     ) -> MacroFuture<'r, 'ast> {
-        (**self).expand(env, arena, args)
+        (**self).expand(env, symbols, arena, args)
     }
 }
 
@@ -457,19 +463,20 @@ impl<'a> MacroExpander<'a> {
             exprs: Vec::new(),
         };
         visitor.visit_expr(expr);
-        let MacroVisitor { exprs, .. } = visitor;
-        self.expand(arena, exprs).await
+        let MacroVisitor { exprs, symbols, .. } = visitor;
+        self.expand(symbols, arena, exprs).await
     }
 
     async fn expand<'ast>(
         &mut self,
+        symbols: &mut Symbols,
         arena: &mut ast::OwnedArena<'ast, Symbol>,
         mut exprs: Vec<(&'_ mut SpannedExpr<'ast, Symbol>, Arc<dyn Macro>)>,
     ) {
         let mut futures = Vec::with_capacity(exprs.len());
         for (expr, mac) in exprs.drain(..) {
             let result = match &mut expr.value {
-                Expr::App { args, .. } => mac.expand(self, arena, args).await,
+                Expr::App { args, .. } => mac.expand(self, symbols, arena, args).await,
                 _ => unreachable!("{:?}", expr),
             };
             match result {