bottom up vs top down

quicksort :: (Ord a) => [a] -> [a]
quicksort [] = []
quicksort (x:xs) =
    let smallerSorted = quicksort [a | a <- xs, a <= x]
        biggerSorted  = quicksort [a | a <- xs, a > x]
    in  smallerSorted ++ [x] ++ biggerSorted


quicksort :: (Ord a) => [a] -> [a]
quicksort [] = []
quicksort (x:xs) = smallerSorted ++ [x] ++ biggerSorted
    where smallerSorted = quicksort [a | a <- xs, a <= x]
          biggerSorted  = quicksort [a | a <- xs, a > x]