Hi, I'm looking at this: data Stream a = Cons a (Stream a) and with streamFromSeed :: (a -> a) -> a -> Stream a streamFromSeed f a = Cons a (streamFromSeed f (f a)) I can do, for example, evens :: Stream Integer evens = streamFromSeed (+2) 0 what I'd like to do is take one item at a time from the stream. My first shot was next :: (Stream a) -> (Stream a, a) but that means I need to keep a ref to the stream that is returned in the tuple which makes for messy code for subsequent calls to next. I sense that the State monad needs to be involved but I'm not sure exactly how as my experiments with State still required I keep a ref to the 'new' stream. Conceptually I see this as a 'global' state and next is just next :: a but that's 30 years of imperative programming speaking and is, I think, wrong! Any help would be really appreciated. Thanks Mike