Merge Sort (Haskell)

merge-sort.hs

--------------------------------------------------------------------------------
import Data.Function ((&))
--------------------------------------------------------------------------------
main :: IO ()
main =
  [2,3,5,1,4,6,8,7,9] & mergeSort & show & putStrLn

mergeSort :: (Ord a) => [a] -> [a]
mergeSort []  = []
mergeSort [x] = [x]
mergeSort xs  = merge (mergeSort lhs) (mergeSort rhs)
  where
    (lhs, rhs) = splitAt (length xs `div` 2) xs

merge :: (Ord a) => [a] -> [a] -> [a]
merge [] rhs = rhs
merge lhs [] = lhs
merge lhs@(x:xs) rhs@(y:ys)
  | x <= y    = x:(merge xs rhs)
  | otherwise = y:(merge lhs ys)