-- (<*>) :: EitherIO e (a -> b) -> EitherIO e a -> EitherIO e b
  f <*> x = EitherIO w
    where w = (liftA2 (<*>) (runEitherIO f) (runEitherIO x))
  -- f :: EitherIO e (a -> b)
  -- runEitherIO :: EitherIO e a -> IO (Either e a)
  -- runEitherIO f :: IO (Either e (a -> b))

  -- x :: EitherIO e a
  -- runEitherIO x :: IO (Either e x)

  -- liftA2 :: (a -> b -> c) -> EitherIO e a -> EitherIO e b -> EitherIO e c ?????
  -- EitherIO :: IO (Either e c) -> EitherIO e c
  -- w :: IO (Either e c)




instance Monad (EitherIO e) where
  return  = pure
  x >>= f = EitherIO $ runEitherIO x >>= either (return . Left) (runEitherIO . f)