Lazy Lists in Python and C++

In Python, I'd normally use a generator: the language and libraries support you in coding that way. Occasionally you run into the only-iterate-through-once restriction as a problem, and for that I stick a memoizing adaptor in.

I made a toy implementation of this sort of thing in Forth:

http://pastebin.com/vHaU3jPW

This code isn't very well factored, but I think the results are pretty clean looking. With this code:

  : printPair ." ( " . ." , " . ." )" space ;
  1 2 counter 0 5 range zip 1 2 counter 3 7 range zip chain ' printPair map

You get this output:

  ( 0 , 1 ) ( 1 , 3 ) ( 2 , 5 ) ( 3 , 7 ) ( 4 , 9 ) ( 5 , 11 )
  ( 3 , 1 ) ( 4 , 3 ) ( 5 , 5 ) ( 6 , 7 ) ( 7 , 9 )

Lazy title: the author gives examples in Haskell, Python, R, C++, and C++0x.

Is there an explanation of how Python yield is implemented?