Marcus D. Gabriel wrote:
By the way, out or curiosity, how would you generalize your current function replace?
I would define: replaceBy :: ([a] -> ([b], [a])) -> [a] -> [b] replaceBy splt l = case l of [] -> [] _ -> let (ft, rt) = splt l in ft ++ replaceBy splt rt The first argument is a kind of splitting function that expects a non-empty input list to cut of a first part and change this part to the a replacement list of type [b]. The second part must be the rest of the input to be processed. The original replace function can then be defined via: replace :: Eq a => [a] -> a -> [a] -> [a] replace sl@(_ : _) r = replaceBy $ \ l@(hd : tl) -> case stripPrefix sl l of Nothing -> ([hd], tl) Just rt -> ([r], rt) Other replacements are also possible, i.e. replaceDelim :: ([a] -> ([a], [a])) -> [a] -> [Either [a] a] replaceDelim splt = replaceBy $ \ l@(hd : tl) -> let (ft, rt) = splt l in if null ft then ([Right hd], tl) else ([Left ft], rt) For replaceDelim consider an input function like "span isSpace". A sequence of spaces is grouped to a "Left String", whereas other characters become "Right". The resulting list is suitable for my original splitBy function yielding a list of type "[[Either [a] a]]". This result can be further flattened to [[a]] (by the function flatEitherSplits below). splitByDelim :: ([a] -> ([a], [a])) -> [a] -> [[a]] splitByDelim split = flatEitherSplits . splitBy (either (const True) (const False)) . replaceDelim split As a concrete example consider: splitBySpaces :: String -> [String] splitBySpaces = splitByDelim (span isSpace) splitBySpaces "ab c def" == ["ab"," ","c"," ","def"] For the sake of completeness I add the definition of flatEitherSplits that exploits the result structure of splitBy and uses auxiliary functions: flatRight :: [Either [a] a] -> [a] flatRight = map (either (error "flatRight") id) flatEither :: [Either [a] a] -> [[a]] flatEither (Left d : rt) = d : [flatRight rt] flatEitherSplits :: [[Either [a] a]] -> [[a]] flatEitherSplits (h : tl) = flatRight h : concatMap flatEither tl Cheers Christian P.S.
For the general case take my unintercalate below:
splitOnAList sl = intercalate [sl] . map (: []) . unintercalate sl
By the way, this can be expressed simpler: splitOnAList sl = intersperse sl . unintercalate sl