Kata

We have join :

join :: (Monad m) => m (m a) -> m a
join (Just (Just x)) = Just x
join _ = Nothing

So join (Just (Just 1)) evaluates to Just 1, unwrapping extra layers.

We may want to join arbitrarily many nested Maybes, until the type is Maybe a, where a is not Maybe something.

Implement this function, jojo ( join-join-join-..-join so jojo ).

Inspired by @ice1000's Agda kata, of the same name but different intent.