module Exercise_8 where

import Foreign.Marshal.Utils
import Control.Arrow
import Control.Monad
import Data.List
import Data.Maybe
import Data.Function

{-WETT-}
shoefa :: (Num a, Ord a) => [a] -> Int
shoefa = filter toBool              -- remove zeroes
     >>> map signum
     >>> zipWith subtract <*> tail  -- transform to differences of signs    (equals -> 0)
     >>> filter toBool              -- keep only steps with differing signs (values /= 0)
     >>> length

-- Insane arrow infix usage instead of . because . binds more strongly than <*>, which is no good,
-- and we may as well be consistent.

{-MCCOMMENT
  yes but what if we "on" more?
  shoefa' xs = length $ filter id $ on (zipWith $ on (/=) signum) ($ filter (/= 0) xs) id tail
-}
{-TTEW-}