module Stail where

stail :: [a] -> Maybe [a]
stail [] = Nothing
stail (x : xs) =
  case stail xs of
    Nothing -> Just []
    _ -> Just xs

stail2 :: [a] -> Maybe [a]
stail2 [] = Nothing
stail2 (x : xs) =
  Just (case stail2 xs of
          Nothing -> []
          _ -> xs)

stail2Fold :: [a] -> Maybe (a,[a])
stail2Fold = foldr (\ x r -> Just (case r of
                                    Nothing -> (x,[])
                                    Just (y,tl) -> (x , y : tl))) Nothing