quicksort in haskell

quicksort.hs

quicksort :: (Ord a) => [a] -> [a]
quicksort []     = []
quicksort (x:xs) = smaller ++ equal ++ greater
    where smaller = quicksort (filter (<x) xs)
          equal = x:(filter (==x) xs)
          greater = quicksort (filter (>x) xs)