minor clean up (#4069)

lib/utils.js

@@ -112,51 +112,29 @@ function return_this() { return this; }
 function return_null() { return null; }
 
 var List = (function() {
-    function List(a, f, backwards) {
-        var ret = [], top = [], i;
-        function doit() {
+    function List(a, f) {
+        var ret = [];
+        for (var i = 0; i < a.length; i++) {
             var val = f(a[i], i);
-            var is_last = val instanceof Last;
-            if (is_last) val = val.v;
-            if (val instanceof AtTop) {
-                val = val.v;
-                if (val instanceof Splice) {
-                    top.push.apply(top, backwards ? val.v.slice().reverse() : val.v);
-                } else {
-                    top.push(val);
-                }
-            } else if (val !== skip) {
-                if (val instanceof Splice) {
-                    ret.push.apply(ret, backwards ? val.v.slice().reverse() : val.v);
-                } else {
-                    ret.push(val);
-                }
-            }
-            return is_last;
-        }
-        if (Array.isArray(a)) {
-            if (backwards) {
-                for (i = a.length; --i >= 0;) if (doit()) break;
-                ret.reverse();
-                top.reverse();
+            if (val === skip) continue;
+            if (val instanceof Splice) {
+                ret.push.apply(ret, val.v);
             } else {
-                for (i = 0; i < a.length; ++i) if (doit()) break;
+                ret.push(val);
             }
-        } else {
-            for (i in a) if (HOP(a, i)) if (doit()) break;
         }
-        return top.concat(ret);
+        return ret;
     }
     List.is_op = function(val) {
-        return val === skip || val instanceof AtTop || val instanceof Last || val instanceof Splice;
+        return val === skip || val instanceof Splice;
+    };
+    List.splice = function(val) {
+        return new Splice(val);
     };
-    List.at_top = function(val) { return new AtTop(val); };
-    List.splice = function(val) { return new Splice(val); };
-    List.last = function(val) { return new Last(val); };
     var skip = List.skip = {};
-    function AtTop(val) { this.v = val; }
-    function Splice(val) { this.v = val; }
-    function Last(val) { this.v = val; }
+    function Splice(val) {
+        this.v = val;
+    }
     return List;
 })();