wtf.hs

module Wtf where

import Control.Applicative ((<$))
import Data.List (unfoldr)


(.:) :: (Functor f, Functor g) => (a -> b) -> f (g a) -> f (g b)
(.:) = fmap . fmap


shorter :: [a] -> [b] -> Bool
shorter xs ys = (() <$ xs) < (() <$ ys)

iter :: (Eq a, Num a) => [a] -> [a] -> [a]
iter xs ys = dropWhile (== 0) $ zipWith (abs .: (-)) xs (ys ++ repeat 0)

-- >>> wtf [1,1,0,1,0] [1,1,1]
-- [[1,1,0,1,0],[1,1,0],[1]]
wtf :: (Eq a, Num a) => [a] -> [a] -> [[a]]
wtf xs ys = xs : unfoldr (\xs' ->
  if shorter xs' ys
     then Nothing
     else let xs'' = iter xs' ys in Just (xs'', xs'')) xs

-- >>> foo [1,1,0,1,0] [1,1,1]
-- [1]
foo :: (Eq a, Num a) => [a] -> [a] -> [a]
foo = last .: wtf