[Haskell-beginners] Iterating a monadic action with memoization

[Alex]

Brent Yorgey <byorgey <at> seas.upenn.edu> writes:

[...]
> 
> 
> How about this?
> 
>   iterateM :: Monad m => (a -> m a) -> a -> m [a]
>   iterateM f a = (a:) `liftM` (f a >>= iterateM f)
> 
> -Brent
> 
> 
The problem with this is that it is not "lazy" in the sense that

inc :: Int -> IO Int
inc x = (print x) >> return $! x + 1

main = do
  xs <- liftM (take 5) $ iterateM inc 0
  print xs

will never terminate. It will keep printing all natural numbers but 
it will never print the list xs. I don't quite understand why this is
so, nor do I know how to rewrite iterateM to get the desired behavior.
But I wish someone would enlighten me :-)