My TCO -- doesn't work with mutual recursion

gistfile1.txt

function toArray(obj, i) {
    return Array.prototype.slice.call(obj, i || 0);
}

function tco(fn) {
    return function () {
        var args = toArray(arguments),
            shouldContinue = true,
            recur = function () {
                shouldContinue = true;
                return toArray(arguments);
            };

        while ( shouldContinue ) {
            shouldContinue = false;
            args = fn.apply(this, [recur].concat(args));
        }

        return args;
    };
}

var factorial = tco(function (factorial, n, acc) {
    acc = acc || 1;
    return n < 2
        ? acc
        : factorial(n - 1, acc * n);
});

factorial(170);