> You don't actually have to handle I/O with the async runtime if you don't want. You _could_ just poll the futures yourself in a loop, which is roughly the same as what happens if you just call the transition function in a loop for a manual state machine.

How would the future get the I/O result then?

> And likewise if you just keep calling the transition function with empty input you'll also busy-loop.

This makes no sense, why would I ever want to do that?

> but if you've got your own external notion of that

That's a very big if. I said "easily" and this is not easy at all.

Moreover it ignores the context: the SansIO/async/await code is generally a library written by a user, while the code that wants to use it is written by someone else entirely. Good luck sharing this external notion between the two!

---

I agree that it would be ideal to have a way to automatically generate the state machine from straightforward looking code, and async/await kinda does this, but this usecase requires more flexibility than what async/await provides.