sort :: Ord a => [a] -> [a]

sort []         =  []
sort [x]        =  [x]
sort xs         =  merge (sort ys) (sort zs)
  where 
      (ys,zs) =  splitAt (length xs `div` 2) xs
       merge [] y=y
       merge x []=x
       merge (x:xs) (y:ys)
         | x <= y = x:merge xs (y:ys)
         | otherwise = y:merge (x:xs) ys

sort[15,20,31,39, 40, 43, 50]