-- | A traversal which focuses on each element in any 
-- Traversable container.
-- >_> (a -> App b) -> (f a -> App $ f b)
elements :: T.Traversable f => Traversal (f a) (f b) a b
elements = traverse
elements :: T.Traversable f => Traversal (f a) (f b) a b
elements = traverse
elements = traverse