Improved merge sort in haskell!

Main.hs

module Main where

import System.Environment

main :: IO ()
main = do
  args <- getArgs
  mapM_ putStrLn $ sort args

sort :: (Ord a) => [a] -> [a]
sort xs = reduce True $ map (arr) xs

arr :: a -> [a]
arr x = [x]

reduce :: (Ord a) => Bool -> [[a]] -> [a]
reduce _ []            = []
reduce forwards (x:[]) = if forwards then x else reverse x
reduce forwards xs     = reduce (not forwards) (combine forwards [] xs)

combine :: (Ord a)   => Bool -> [[a]] -> [[a]] -> [[a]]
combine forwards acc []       = acc
combine forwards acc (x:[])   = (reverse x):acc
combine forwards acc (x:y:zs) = let merged = merge forwards x y
                                    acc'   = merged:acc
                                in  combine forwards acc' zs

merge :: (Ord a) => Bool -> [a] -> [a] -> [a]
merge forwards xs ys = mergeIter forwards [] xs ys

mergeIter :: (Ord a) => Bool -> [a] -> [a] -> [a] -> [a]
mergeIter _        acc [] []     = acc
mergeIter forwards acc (x:xs) [] = mergeIter forwards (x:acc) xs []
mergeIter forwards acc [] (y:ys) = mergeIter forwards (y:acc) [] ys
mergeIter forwards acc (x:xs) (y:ys)
    | x <=  y && forwards     = mergeIter forwards (x:acc) xs (y:ys)
    | x > y && not forwards   = mergeIter forwards (x:acc) xs (y:ys)
    | otherwise               = mergeIter forwards (y:acc) (x:xs) ys