simple javascript task framework to flip recursion inside out

gistfile1.js

function serializeArgs(args) {
  return JSON.stringify(args);
}

function unroll(f) {
  if (f._cache == undefined)
    f._cache = {};

  var f_new = function() {
    var key = serializeArgs(arguments);
    if (f._cache[key] != undefined)
      return f._cache[key];
    else
      throw f_new.task.apply(null, arguments);
  }

  f_new.task = function() {
    var task = function() {
      var task = arguments.callee; // same
      return runTasks([task]);
    }
    var args = arguments;
    task.run = function() {
      var result = f.apply(null, args);
      var key = serializeArgs(args);
      f._cache[key] = result;
      return result;
    }
    return task;
  }

  return f_new;
}

function runTasks(tasks) {
  while (tasks.length > 0) {
    var nextTask = tasks.pop();
    try {
      // We're running this synchronously, but it could also be async
      var result = nextTask.run();
    } catch(anotherTask) {
      tasks.push(nextTask);
      tasks.push(anotherTask);
    }
  }
  return result;
}

var fib = unroll(function(x) {
  return x > 1 ? fib(x-1) + fib(x-2) : x;
});

var factorial = unroll(function(x) {
  return x > 0 ? x * factorial(x-1) : 1;
});

var nChooseK = unroll(function(n, k) {
  return factorial(n) / factorial(k) / factorial(n - k);
});

// Mutual recursion
var isOdd = unroll(function(n) { return n == 0 ? false : !isEven(n-1); });
var isEven = unroll(function(n) { return n == 0 ? true: !isOdd(n-1); });

var t1 = fib.task(43);
var t2 = factorial.task(10);
var t3 = nChooseK.task(12, 7);
var t4 = isEven.task(39);

console.log(t1());
console.log(t2());
console.log(t3());
console.log(t4());