adding slightly optimized syntax for range comprehensions that could care less about the index variable. Issue #547

lib/grammar.js

@@ -389,15 +389,24 @@
       })
     ],
     For: [
-      o("Statement ForStart ForSource", function() {
+      o("Statement ForBody", function() {
-        $3.raw = $2.raw;
+        return new ForNode($1, $2, $2.vars[0], $2.vars[1]);
-        return new ForNode($1, $3, $2[0], $2[1]);
+      }), o("Expression ForBody", function() {
-      }), o("Expression ForStart ForSource", function() {
+        return new ForNode($1, $2, $2.vars[0], $2.vars[1]);
-        $3.raw = $2.raw;
+      }), o("ForBody Block", function() {
-        return new ForNode($1, $3, $2[0], $2[1]);
+        return new ForNode($2, $1, $1.vars[0], $1.vars[1]);
-      }), o("ForStart ForSource Block", function() {
+      })
+    ],
+    ForBody: [
+      o("FOR Range", function() {
+        return {
+          source: new ValueNode($2),
+          vars: []
+        };
+      }), o("ForStart ForSource", function() {
         $2.raw = $1.raw;
-        return new ForNode($3, $2, $1[0], $1[1]);
+        $2.vars = $1;
+        return $2;
       })
     ],
     ForStart: [

lib/nodes.js

@@ -1435,7 +1435,7 @@
         return n instanceof CodeNode;
       });
       scope = o.scope;
-      name = this.name && this.name.compile(o);
+      name = (this.name && this.name.compile(o)) || scope.freeVariable();
       index = this.index && this.index.compile(o);
       if (name && !this.pattern && !codeInBody) {
         scope.find(name);

src/grammar.coffee

@@ -425,9 +425,14 @@ grammar = {
   # Comprehensions can either be normal, with a block of expressions to execute,
   # or postfix, with a single expression.
   For: [
-    o "Statement ForStart ForSource",           -> $3.raw = $2.raw; new ForNode $1, $3, $2[0], $2[1]
+    o "Statement ForBody",                      -> new ForNode $1, $2, $2.vars[0], $2.vars[1]
-    o "Expression ForStart ForSource",          -> $3.raw = $2.raw; new ForNode $1, $3, $2[0], $2[1]
+    o "Expression ForBody",                     -> new ForNode $1, $2, $2.vars[0], $2.vars[1]
-    o "ForStart ForSource Block",               -> $2.raw = $1.raw; new ForNode $3, $2, $1[0], $1[1]
+    o "ForBody Block",                          -> new ForNode $2, $1, $1.vars[0], $1.vars[1]
+  ]
+
+  ForBody: [
+    o "FOR Range",                              -> {source: new ValueNode($2), vars: []}
+    o "ForStart ForSource",                     -> $2.raw = $1.raw; $2.vars = $1; $2
   ]
 
   ForStart: [

src/nodes.coffee

@@ -1279,7 +1279,7 @@ exports.ForNode = class ForNode extends BaseNode
     source        = if range then @source.base else @source
     codeInBody    = @body.contains (n) -> n instanceof CodeNode
     scope         = o.scope
-    name          = @name and @name.compile o
+    name          = (@name and @name.compile(o)) or scope.freeVariable()
     index         = @index and @index.compile o
     scope.find name  if name and not @pattern and not codeInBody
     scope.find index if index

test/test_comprehensions.coffee

@@ -126,3 +126,9 @@ all = value for all key, value of whiskers
 
 ok own.join(' ') is 'Whiskers'
 ok all.sort().join(' ') is 'Whiskers cream tabby'
+
+
+# Optimized range comprehensions.
+exxes = 'x' for [0...10]
+ok exxes.join(' ') is 'x x x x x x x x x x'
+