qsort [] = []
qsort (p:xs) = qsort lt ++ [p] ++ qsort gt
  where (lt, gt) = partition ((>) p) xs

partition1 _ [] = ([], [])
partition1 f (x:xs) = 
  let (ys, zs) = partition1 f xs
  in if f x 
    then (x:ys, zs)
    else (ys, x:zs)

partition _ [] = ([], [])
partition f (x:xs)
  | f x       = (x:ys, zs)
  | otherwise = (ys, x:zs)
  where (ys, zs) = partition f xs

main = do
let li = [5,1,4,2,3]
putStrLn $ show $ qsort li