Quicksort, Idris style

quicksort.idr

module Main

-- data List a = (::) a (List a) | Nil

quicksort : Ord a => List a -> List a

quicksort [] = []
quicksort (x :: xs) = (sort lower) ++ [x] ++ (sort upper)
  where lower = filter (<x) xs
        upper = filter (>=x) xs

main : IO ()
main = traverse_ printLn
  [ quicksort [3, 2, 1, 0, -1, -2, -3]
  , quicksort [4, 2, 0, 1, 3, 5]
  , quicksort [2, 1]
  , quicksort [1]
  ]