mergesort implementation for learning Haskell

mergesort.hs

import Debug.Trace

main :: IO()
main = do
  let sorted = mergeSort [6, 5, 3, 1, 8, 7, 2, 4]
  print sorted

mergeSort :: (Ord a, Show a) => [a] -> [a]
-- mergeSort lst | trace ("sorting: " ++ show lst) False = undefined
mergeSort [] = []
mergeSort [x] = [x]
mergeSort list =
  merge (mergeSort left) (mergeSort right)
  where (left, right) = partition list

partition :: [a] -> ([a], [a])
partition list =
  splitAt pivot list
  where pivot = length list `quot` 2

merge :: (Ord a, Show a) => [a] -> [a] -> [a]
-- merge first second | trace ("merging: " ++ show first ++ " " ++ show second) False = undefined
merge [] [] = []
merge first [] = first
merge [] second = second
merge left@(x:xs) right@(y:ys)
  | x > y = x : merge xs right
  | otherwise = y : merge left ys