It depends on what you mean by "swallows values". If I have an IO<T>, I can very easily get at the T that's inside by flatMapping over it. It's true that there'

It depends on what you mean by "swallows values". If I have an IO<T>, I can very easily get at the T that's inside by flatMapping over it. It's true that there's no way to turn an IO<T> straight into a T -- whatever you do with the T must always get wrapped back in IO<-> at the end of the day -- but it's not gone, and indeed we do use monads to store state. (There's literally a monad called `State`, actually.) What monads don't let you get at -- at least, not without more knowledge about which monad you're using -- is whatever other information given alongside the Ts it contains. If I've got a random M<T>, and I don't know that M is Option, I can only operate over all the Ts (the either zero or one of them) it contains, but I can't tell whether it has any Ts in the first place.