3 files changed, 30 insertions, 10 deletions
diff --git a/src/comp/front/ast.rs b/src/comp/front/ast.rs
index 1425db61..a7ef4e65 100644
--- a/src/comp/front/ast.rs
+++ b/src/comp/front/ast.rs
@@ -83,7 +83,7 @@ tag decl_ {
 type expr = spanned[expr_];
 tag expr_ {
     expr_vec(vec[@expr]);
-    expr_tup(vec[@expr]);
+    expr_tup(vec[tup(bool /* mutability */, @expr)]);
     expr_rec(vec[tup(ident,@expr)]);
     expr_call(@expr, vec[@expr]);
     expr_binary(binop, @expr, @expr);
diff --git a/src/comp/front/parser.rs b/src/comp/front/parser.rs
index 597d578f..8d945dd8 100644
--- a/src/comp/front/parser.rs
+++ b/src/comp/front/parser.rs
@@ -219,6 +219,18 @@ io fn parse_name(parser p, ast.ident id) -> ast.name {
     ret spanned(lo, tys.span, rec(ident=id, types=tys.node));
 }
 
+io fn parse_possibly_mutable_expr(parser p) -> tup(bool, @ast.expr) {
+    auto mut;
+    if (p.peek() == token.MUTABLE) {
+        p.bump();
+        mut = true;
+    } else {
+        mut = false;
+    }
+
+    ret tup(mut, parse_expr(p));
+}
+
 io fn parse_bottom_expr(parser p) -> @ast.expr {
 
     auto lo = p.get_span();
@@ -239,11 +251,11 @@ io fn parse_bottom_expr(parser p) -> @ast.expr {
 
         case (token.TUP) {
             p.bump();
-            auto pf = parse_expr;
-            auto es = parse_seq[@ast.expr](token.LPAREN,
-                                           token.RPAREN,
-                                           some(token.COMMA),
-                                           pf, p);
+            auto pf = parse_possibly_mutable_expr;
+            auto es = parse_seq[tup(bool, @ast.expr)](token.LPAREN,
+                                                      token.RPAREN,
+                                                      some(token.COMMA),
+                                                      pf, p);
             hi = es.span;
             ex = ast.expr_tup(es.node);
         }
diff --git a/src/comp/middle/fold.rs b/src/comp/middle/fold.rs
index 543a05e1..5445d3c1 100644
--- a/src/comp/middle/fold.rs
+++ b/src/comp/middle/fold.rs
@@ -47,7 +47,7 @@ type ast_fold[ENV] =
          vec[@expr] es) -> @expr)                 fold_expr_vec,
 
      (fn(&ENV e, &span sp,
-         vec[@expr] es) -> @expr)                 fold_expr_tup,
+         vec[tup(bool,@expr)] es) -> @expr)       fold_expr_tup,
 
      (fn(&ENV e, &span sp,
          vec[tup(ident,@expr)] fields) -> @expr)  fold_expr_rec,
@@ -161,6 +161,11 @@ fn fold_exprs[ENV](&ENV env, ast_fold[ENV] fld, vec[@expr] e) -> vec[@expr] {
     ret _vec.map[@expr, @expr](fe, e);
 }
 
+fn fold_tup_entry[ENV](&ENV env, ast_fold[ENV] fld, &tup(bool,@expr) e)
+    -> tup(bool,@expr) {
+    ret tup(e._0, fold_expr(env, fld, e._1));
+}
+
 fn fold_rec_entry[ENV](&ENV env, ast_fold[ENV] fld, &tup(ident,@expr) e)
     -> tup(ident,@expr) {
     ret tup(e._0, fold_expr(env, fld, e._1));
@@ -181,8 +186,10 @@ fn fold_expr[ENV](&ENV env, ast_fold[ENV] fld, &@expr e) -> @expr {
         }
 
         case (ast.expr_tup(?es)) {
-            auto ees = fold_exprs(env_, fld, es);
-            ret fld.fold_expr_vec(env_, e.span, ees);
+            let operator[tup(bool,@expr), tup(bool,@expr)] fe =
+                bind fold_tup_entry[ENV](env, fld, _);
+            auto ees = _vec.map[tup(bool,@expr), tup(bool,@expr)](fe, es);
+            ret fld.fold_expr_tup(env_, e.span, ees);
         }
 
         case (ast.expr_rec(?es)) {
@@ -425,7 +432,8 @@ fn identity_fold_expr_vec[ENV](&ENV env, &span sp, vec[@expr] es) -> @expr {
     ret @respan(sp, ast.expr_vec(es));
 }
 
-fn identity_fold_expr_tup[ENV](&ENV env, &span sp, vec[@expr] es) -> @expr {
+fn identity_fold_expr_tup[ENV](&ENV env, &span sp, vec[tup(bool, @expr)] es)
+        -> @expr {
     ret @respan(sp, ast.expr_tup(es));
 }