simple visitor API and code to figure out scope and references

lib/utils.js

@@ -62,3 +62,38 @@ function defaults(args, defs) {
     }
     return ret;
 };
+
+function noop() {};
+
+var MAP = (function(){
+    function MAP(a, f, o) {
+        var ret = [], top = [], i;
+        function doit() {
+            var val = f.call(o, a[i], i);
+            if (val instanceof AtTop) {
+                val = val.v;
+                if (val instanceof Splice) {
+                    top.push.apply(top, val.v);
+                } else {
+                    top.push(val);
+                }
+            }
+            else if (val !== skip) {
+                if (val instanceof Splice) {
+                    ret.push.apply(ret, val.v);
+                } else {
+                    ret.push(val);
+                }
+            }
+        };
+        if (a instanceof Array) for (i = 0; i < a.length; ++i) doit();
+        else for (i in a) if (HOP(a, i)) doit();
+        return top.concat(ret);
+    };
+    MAP.at_top = function(val) { return new AtTop(val) };
+    MAP.splice = function(val) { return new Splice(val) };
+    var skip = MAP.skip = {};
+    function AtTop(val) { this.v = val };
+    function Splice(val) { this.v = val };
+    return MAP;
+})();