/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.

>>8
It looks like F# for the .NET Framework, but it's using the same underlying .NET/CLI yield mechanism that C# uses. Perhaps you should have been more clear about this.