/prog/ challenge (S(SKK)(SKK))(S(SKK)(SKK))

The challenge: Implement generators in the favourite language of yours.
Are banned: Language native generators (i.e. FIOC's yield), delimited continuations (sorry, Schemers, that would be too easy).

The test program will be an infinite generator that computes facts, and a loop that takes the first five of them.

The deadline is 17/04/2011 00:00 /prog/time.
The most complete, small and easy to use implementation wins.

>>52
I programmed it that way so the entire factorial function would be encapsulated into one method. Its encapsulated because that's what you would have to do in order to extend the Generator class and implement a new value generating method. You've got to think like an enterprise businessman here.