On 05/31/2011 04:48 PM, Artyom Kazak wrote:
Oh, sorry. I was unclear. I have meant "assuming IO is lazy", as Yves wrote.
Ah, ok. That makes more sense.
And saying "some hacks" I meant unsafeInterleaveIO, which lies beneath the laziness of, for example, getContents.
Which explains why assuming getContents is strict has never worked for me. I'm trying to implement unfoldM1 without using unsafeIO, if possible. Since unfoldM1 f l = do next <- f l rest <- unfoldM1 f (next : l) return (next : rest) obviously won't work, I've been trying to use fmap unfoldM1 :: (Functor m, Monad m) => ([a] -> m a) -> [a] -> m [a] unfoldM1 f l = do next <- f l fmap (next :) $ unfoldM1 f (next : l) Evaluation here also doesn't terminate (or, (head $ unfoldM (return . head)) doesn't), although I can't figure out why. fmap shouldn't need to fully evaluate a list to prepend an element, right?