extract an enclosed sublist

extract.hs

extract :: Eq a => [a] -> [a] -> [a] -> Maybe [a]
extract start end xs = do
  ys <- snd <$> split start xs
  fst <$> split end ys

split :: Eq a => [a] -> [a] -> Maybe ([a], [a])
split p = go id
  where
    go _ [] = Nothing
    go f xt@(x : xs) =
      case match p xt of
        Nothing -> go (f . (x :)) xs
        Just rs -> Just (f [], rs)

match :: Eq a => [a] -> [a] -> Maybe [a]
match [] rs = Just rs
match _ [] = Nothing
match (x : xs) (y : ys)
  | x == y = match xs ys
  | otherwise = Nothing