Hello,
So I'm clearly expecting ghc to be more psychic than it's currently capable. But what I'd like to do is pass an infinite list through a processing function which maintains some state (foo could easily be a pseudo random number generator), and take the first bit of it.
Any help?
Intuitively, your state is flowing from the end of the list back towards the beginning in your code. If you really want a right fold where the state flows from left to right, you could try this: foldrSt st f v [] = v st foldrSt st f v (x:xs) = let (st', f') = f st x in f' (foldrSt st' f v xs) and then rewrite foo as: foo payload x = (payload, (\l -> x:l)) then: take 10 $ foldrSt Nothing foo (\st -> []) [1..] evaluates to [1 .. 10]. -Jeff