Not directly answering your question, but what you need is called
coroutines, and there are better monads for that purpose.  This is how
the Cont monads are defined:

    newtype Cont r a = Cont ((a -> r) -> r)

But what you really need here is called a Coroutine monad:

    newtype Coroutine f a = Coroutine (Either (f (Coroutine f a)) a)

Don't worry about that scary type, because if you look closely you will
find that this is just Free as defined in the 'free' package:

    data Free f a
        = Free (f (Free f a))
        | Pure a