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

.++ as bs = case as of
    Nil => bs
    Cons x xs => Cons x (xs ++ bs)

.<= a b = case a < b of
    False => a == b
    True => True

quicksort xs = case xs of
    Nil => Nil
    Cons a as => quicksort (filter (\y. a < y) xs) ++ (Cons a (quicksort (filter (\y. y <= a)) xs))

head xs = case xs of
    Cons a _ => a

main : Int
main = head (quicksort (Cons 9 (Cons 8 (Cons 7 (Cons 6 (Cons 5 (Cons 4 (Cons 3 (Cons 2 (Cons 1 (Cons 0 Nil)))))))))))