qsort [] = []
qsort (p:xs) =  
  let (lt, gt) = partition' ((>) p) xs
  in qsort lt ++ [p] ++ qsort gt

partition' _ [] = ([], [])
partition' f (x:xs) =
  let (accepted, rejected) = partition' f xs
  in if f x then (x:accepted, rejected)
     else (accepted, x:rejected)

main = do
  print $ qsort [3,1,2]
  print $ partition' odd [1,2,3,4,5]