Blogger - HTIF - difference

-- |Finds symmetric difference between lists. O(2nlogn + 2n)
difference :: Ord a => [a] -> [a] -> [a]
difference = iter diffF

diffF :: Eq a => (Maybe a, Maybe a) -> [a] -> [a]
diffF (Just x, Just y) acc = if x /= y then x:y:acc else acc
diffF (Just x, Nothing) acc = x:acc
diffF (Nothing, Just y) acc = y:acc
diffF _ acc = acc