On further thought... as you've described it, isn't a monad ("sequential type") basically syntactic sugar around &&? That is, if you write A && B && C and A is false, you stop, or if A is true but B is false, you stop. I said "basically" because it's not strictly boolean with the None stuff and Futures are their own oddity, but from 20,000 feet, is this a fair comparison or have I missed something fundamental?