filter : (a -> Bool) -> List a -> List a
filter p xs = case xs of
    Nil => Nil
    Cons x xs => case p x of
        True => Cons x (filter p xs)
        False => filter p xs

quicksort : List Int -> List Int
quicksort xs = case xs of
    Nil => Nil
    Cons a as => let smaller = quicksort (filter (\y. y < a) xs) in
                 let bigger = quicksort (filter (\y. a < y) xs) in
                 smaller ++ (Cons a bigger)

mkDescList : Int -> Int -> List Int
mkDescList from to = case from == to of
    True => Nil
    False => Cons from (mkDescList (from - 1) to)    
    
main = printList (quicksort (mkDescList 1000 0))