Using a typeof check in scope.

lib/scope.js

@@ -13,6 +13,7 @@
             type: 'arguments'
           }
         ];
+        this.positions = {};
         if (this.parent) {
           this.garbage = this.parent.garbage;
         } else {
@@ -25,19 +26,11 @@
     })();
     Scope.root = null;
     Scope.prototype.add = function(name, type) {
-      var _len, _ref2, i, variable;
-      _ref2 = this.variables;
-      for (i = 0, _len = _ref2.length; i < _len; i++) {
-        variable = _ref2[i];
-        if (variable.name === name) {
-          this.variables[i].type = type;
-          return;
-        }
-      }
-      return this.variables.push({
+      var pos;
+      return typeof (pos = this.positions[name]) === 'number' ? this.variables[pos].type = type : this.positions[name] = this.variables.push({
         name: name,
         type: type
-      });
+      }) - 1;
     };
     Scope.prototype.startLevel = function() {
       this.garbage.push([]);

src/scope.coffee

@@ -19,6 +19,7 @@ exports.Scope = class Scope
   # it wraps.
   constructor: (@parent, @expressions, @method) ->
     @variables = [{name: 'arguments', type: 'arguments'}]
+    @positions = {}
     if @parent
       @garbage = @parent.garbage
     else
@@ -27,11 +28,10 @@ exports.Scope = class Scope
 
   # Adds a new variable or overrides an existing one.
   add: (name, type) ->
-    for variable, i in @variables
-      if variable.name is name
-        @variables[i].type = type
-        return
-    @variables.push {name, type}
+    if typeof (pos = @positions[name]) is 'number'
+      @variables[pos].type = type
+    else
+      @positions[name] = @variables.push({name, type}) - 1
 
   # Create a new garbage level
   startLevel: ->