On 03/06/2009 22:26, Sebastian Fischer wrote:
------- {-# LANGUAGE RankNTypes #-}
newtype S a = S { unS :: forall b . (a -> Int -> [b]) -> Int -> [b] }
ret x = S (\c -> c x) a `bind` f = S (\c -> unS a (\x -> unS (f x) c)) zero = S (\c _ -> []) plus a b = S (\c -> id (\d -> if d==0 then [] else id (unS a c) (d-1) ++ id (unS b c) (d-1)))
runS :: S a -> [a] runS a = concatMap (\d -> id (run a) d) [10000]
run :: S a -> Int -> [a] run a = unS a (\x _ -> [x])
natSum :: S Int natSum = anyof [1..] `bind` \x -> anyof [1..] `bind` \y -> ret (x+y) where anyof = foldr plus zero . map ret
main = print . length $ runS natSum -------
Those two [1..] ring alarm bells. GHC will happily combine them with CSE and possibly also lift them to the top-level; both transformations might have a big impact on space behaviour. Try with -fno-full-laziness and/or -fno-cse. Cheers, Simon