gistfile1.hs

(x:xs) `minus` yys@(y:ys)
  | x == y    =     xs `minus` ys
  | otherwise = x : xs `minus` yys

naturals = [1..]
evens    = [2,4..]
odds     = naturals `minus` evens

{-

*Main> take 10 naturals
  [1,2,3,4,5,6,7,8,9,10]
*Main> take 10 odds
  [1,3,5,7,9,11,13,15,17,19]
*Main> take 10 evens
  [2,4,6,8,10,12,14,16,18,20]

-}