Memoized Y-combinator

yc.js

// Y-combinator with memoization
var Yc = function (f, x) {
  x = x || {};

  return function () {
    var y = JSON.stringify([].slice.call(arguments));

    return x[y] || (x[y] = f(function (z) {
      return Yc(f, x)(z);
    }).apply(this, arguments));
  };
};

Slightly improved hashing. (Borrowed from Addy's blog)

Array.prototype.slice.call(arguments)
[].slice.call(arguments)

If you look at the revisions, that's what I had originally. I copy/pasted the var and while statement from the blog post noted in my previous comment, so my version ([].slice.call(arguments)) got replaced by Addy's version. :P

:P