qsort [] = []
qsort (x:xs) = qsort lt ++ [x] ++ qsort gt
  where 
    (lt, gt) = partition' (\a -> a <= x) xs
    
partition' _ [] = ([], [])
partition' f (x:xs)
  | f x       = ((x:accepted), rejected)
  | otherwise = (accepted, (x:rejected))
  where (accepted, rejected) = partition' f xs
  
main = do
  print $ qsort [3,4,1,2]
  print $ partition' odd [1,2,3,4]