function aloop (n, f) {
    var i   = 0;
    var end = new Object;
    var ret = null;
    return Deferred.next(function () {
        var t = (new Date()).getTime();
        try {
            do {
                ret = f(i)
                i++;
                if (i >= n) throw end;
            } while ((new Date()).getTime() - t < 20);
            return Deferred.call(arguments.callee);
        } catch (e) {
            if (e == end) {
                return ret;
            } else {
                throw e;
            }
        }
    });
}