FLOLAC 2018 Week 1 -- nub: filter out duplicating integers on a list

nub.hs

nub' :: [Int] -> [Int] -> [Int]

nub' rs []     = reverse rs
nub' rs (x:xs) | elem x rs = nub'    rs  xs
               | otherwise = nub' (x:rs) xs

nub :: [Int] -> [Int]

nub = nub' []

{-
some test cases:
  * nub [] == []
  * nub [1, 2, 3, 4] == [1, 2, 3, 4]
  * nub [1, 1, 1, 2] == [1, 2]
  * nub [1, 2, 2, 5, 3, 5] == [1, 2, 5, 3]
  * nub [1, 2, 3, 4, 2, 3, 1, 5, 4, 3] == [1, 2, 3, 4, 5]
-}