add let support

lib/ast.js

@@ -547,6 +547,10 @@ var AST_Const = DEFNODE("Const", null, {
     $documentation: "A `const` statement"
 }, AST_Definitions);
 
+var AST_Let = DEFNODE("Let", null, {
+    $documentation: "A `let` statement"
+}, AST_Definitions);
+
 var AST_VarDef = DEFNODE("VarDef", "name value", {
     $documentation: "A variable declaration; only appears in a AST_Definitions node",
     $propdoc: {

lib/output.js

@@ -934,6 +934,9 @@ function OutputStream(options) {
     DEFPRINT(AST_Const, function(self, output){
         self._do_print(output, "const");
     });
+    DEFPRINT(AST_Let, function(self, output){
+        self._do_print(output, "let");
+    });
 
     function parenthesize_for_noin(node, output, noin) {
         if (!noin) node.print(output);

lib/parse.js

@@ -844,6 +844,9 @@ function parse($TEXT, options) {
               case "var":
                 return tmp = var_(), semicolon(), tmp;
 
+              case "let":
+                return tmp = let_(), semicolon(), tmp;
+
               case "const":
                 return tmp = const_(), semicolon(), tmp;
 
@@ -916,7 +919,9 @@ function parse($TEXT, options) {
         if (!is("punc", ";")) {
             init = is("keyword", "var")
                 ? (next(), var_(true))
-                : expression(true, true);
+                : is("keyword", "let")
+                ? (next(), let_(true))
+                :expression(true, true);
             if (is("operator", "in")) {
                 if (init instanceof AST_Var && init.definitions.length > 1)
                     croak("Only one variable declaration allowed in for..in loop");
@@ -1111,6 +1116,14 @@ function parse($TEXT, options) {
         });
     };
 
+    var let_ = function(no_in) {
+        return new AST_Let({
+            start       : prev(),
+            definitions : vardefs(no_in, false),
+            end         : prev()
+        });
+    };
+
     var new_ = function() {
         var start = S.token;
         expect_token("operator", "new");