homework.hs

mergesort :: Ord a => [a] -> [a]
mergesort []                       = []
mergesort [x]                      = [x]
mergesort (split -> (left, right)) = merge (mergesort left) (mergesort right) 
    where merge []       rs = rs
          merge ls       [] = ls
          merge (l : ls) (r : rs)
              | l < r     = l : merge ls (r : rs)
              | otherwise = r : merge (l : ls) rs