/*@
Ox.cache <f> Memoize a function
    <script>
        var f = Ox.cache(function(n) { return n * Math.random(); });
    </script>
    > f(10) == f(10);
    true
    > f(10) == f.clear()(10);
    false
@*/
Ox.cache = function(fn) {
    var cache = {},
        ret = function() {
            var key = JSON.stringify(Ox.makeArray(arguments));
            return key in cache ? cache[key]
                : (cache[key] = fn.apply(this, arguments));
        };
    ret.clear = function() {
        if (arguments.length == 0) {
            cache = {};
        } else {
            Ox.toArray(arguments).forEach(function(key) {
                delete cache[key];
            });
        }
        return ret;
    }
    return ret;
};