Does ZipList have any useful monad instance? The thought came up while thinking about higher order dataflows and an ArrowApply interface for Yampa. As a ZipList can be thought of as a function with a discrete domain, I figured its monadic form could be analogous to the reader monad, hence: instance Monad ZipList where return = ZipList . repeat ZipList xs >>= f = ZipList $ zipWith ((!!) . getZipList . f) xs [0..] Correct me if I'm wrong, but it seems to me that f always returning an infinite list is a sufficient condition for the monad laws to hold. However, this is painfully inefficient. I assume that bringing FRP-like switching and some clever data structure (which optimises stateless streams for starters) into the picture can potentially lead to constant-time access at least in the case of sequential sampling. Is there any recent work going in this direction? Gergely -- http://www.fastmail.fm - One of many happy users: http://www.fastmail.fm/docs/quotes.html