Merge sorting and Insertion sorting in Haskell

sort.hs

module Main where

main :: IO ()
main = pure ()

-- Source: https://youtu.be/PV8_scc1s3g

-------------------------------------------------------------------------------
--                               insertion sort                              --
-------------------------------------------------------------------------------
-- Insert an element in a sorted list
insert :: Int -> [Int] -> [Int]
insert x [] = [x]
insert x (y:ys)
  | x <= y = x : y : ys
  | otherwise = y : insert x ys

-- insert sort a list
isort :: [Int] -> [Int]
-- isort [] = []
-- isort (x:xs) = insert x (isort xs)
isort = foldr insert []

-------------------------------------------------------------------------------
--                                 merge sort                                --
-------------------------------------------------------------------------------
-- Merge two sorted lists
merge :: [Int] -> [Int] -> [Int]
merge [] ys = ys
merge xs [] = xs
merge (x:xs) (y:ys)
  | x <= y = x : merge xs (y : ys)
  | otherwise = y : merge (x : xs) ys

mergesort :: [Int] -> [Int]
mergesort [] = []
mergesort [x] = [x]
mergesort l = merge (mergesort (front l)) (mergesort (back l))
  where
    front l = take (length l `div` 2) l
    back l = drop (length l `div` 2) l