> quickSort                     :: (Ord a) => [a] -> [a]
> quickSort []                  =  []
> quickSort (a : as)            =  quickSort [ b | b <- as, b <= a ]
>                               ++ a : quickSort [ b | b <- as, b > a ]
>
> mergeSort                     :: (Ord a) => [a] -> [a]
> mergeSort []                  =  []
> mergeSort [a]                 =  [a]
> mergeSort as                  =  merge (mergeSort bs) (mergeSort cs)
>     where (bs, cs)            =  splitAt (length as `div` 2) as

The worst case execution time of |mergeSort| is $\Theta(n\log n)$.
NB. |splitAt| is given by

< splitAt                       :: Int -> [a] -> ([a], [a])
< splitAt k as                  =  (take k as, drop k as) {-"\enskip."-}