Hi. I want to write a function to split list by list. E.g. if i have input list "aXYbc" and list "XY" is separator, then result should be ["a", "bc"]. And i want to write it using Continuations. Here is my version, which implements following scheme: .. >>= f x(k+1) >>= f x(k+2) >>= f x(k+3) >>= f x(k+4) >>= .. ....(match to sep) ..........>+ | (failed) +<= (continuation backward) <=+ (add to word) | \------->..(match to sep).....+ | (succeed) +------>+.. (match to sep) ..

import qualified Data.Foldable as F import Control.Applicative import Control.Monad.Cont

nullF :: F.Foldable t => t a -> Bool nullF = null . F.toList

addToHeadA :: Alternative f => a -> [f a] -> [f a] addToHeadA x [] = [pure x] addToHeadA x (y : ys) = (pure x <|> y) : ys

type Sep a = [a] -- Word separator. type Res5 f a = [f a] -- Result. data SplitState5 m f a = MaybeSep5 (Sep a) (Res5 f a) (() -> m (SplitState5 m f a)) | Word5 (Res5 f a)

split5M :: (Eq a, F.Foldable t, Alternative f, MonadCont m) => Sep a -> t a -> m (Res5 f a) split5M ks0 xs | nullF xs = return [] | otherwise = F.foldrM go (Word5 [empty]) xs >>= finalize where ksR = reverse ks0 --go :: (Eq a, MonadCont m) => -- a -> SplitState5 m f a -> m (SplitState5 m f a) go _ (MaybeSep5 [] _ h) = h () go x (MaybeSep5 [k] zs _) | x == k = return (Word5 (empty : zs)) go x (MaybeSep5 (k : ks) zs h) | x == k = return (MaybeSep5 ks zs h) | otherwise = h () go x (Word5 zs) = callCC $ \r -> do callCC $ \h -> go x (MaybeSep5 ksR zs h) >>= r return (Word5 (x `addToHeadA` zs)) finalize :: (Alternative f, MonadCont m) => SplitState5 m f a -> m (Res5 f a) finalize (Word5 zs) = return zs finalize (MaybeSep5 _ _ h) = h () >> return undefined

And i have several questions about this implementation: - Is it good CPS implementation? Or there is much simpler and better one? - Can it be improved? - Can i make it more generic? - Would non-CPS implementation be better or simpler, than this one? -- Dmitriy Matrosov