My amateur attempt at writing merge sort in Haskell.

MergeSort.hs

merge :: Ord a => [a] -> [a] -> [a]
merge [] l = l
merge (a:l1) (b:l2)
  | a <= b    = a : merge l1 (b:l2)
  | otherwise = b : merge l2 (a:l1)

mergeSort :: Ord a => [a] -> [a]
mergeSort [] = []
mergeSort [a] = [a]
mergeSort l = 
  merge (mergeSort $ take half l) (mergeSort $ drop half l)
  where half = quot (length l) 2