make Ox.cache work for aynchronous functions

source/Ox/js/Function.js

@@ -9,12 +9,36 @@ Ox.cache <f> Memoize a function
     > Ox.test.fn(10) == Ox.test.fn.clear()(10);
     false
 @*/
-Ox.cache = function(fn) {
+Ox.cache = function(fn, options) {
+    options = Ox.extend({
+        async: false,
+        key: JSON.stringify
+    }, options || {})
     var cache = {},
         ret = function() {
-            var key = JSON.stringify(Ox.makeArray(arguments));
+            var args = Ox.makeArray(arguments),
-            return key in cache ? cache[key]
+                callback,
-                : (cache[key] = fn.apply(this, arguments));
+                key = options.key(args);
+            function callback() {
+                // cache all arguments passed to callback
+                cache[key] = Ox.makeArray(arguments);
+                // call the original callback
+                Ox.last(args).apply(this, arguments);
+            }
+            if (options.async) {
+                if (!(key in cache)) {
+                    // call function with patched callback
+                    fn.apply(this, Ox.merge(Ox.sub(args, 0, -1), callback));
+                } else {
+                    // call callback with cached arguments
+                    callback.apply(this, cache[key])
+                }
+            } else {
+                if (!(key in cache)) {
+                    cache[key] = fn.apply(this, args);
+                }
+                return cache[key];
+            }
         };
     ret.clear = function() {
         if (arguments.length == 0) {