Comment by Twey

> What if I want to change some state in-between two state transitions (i.e. between two `await` points)?

I think as phrased what you said is an _advantage_ of the Rust model: the state of your state machine is entirely contained within the dedicated state-machine type and you know its behaviour can't depend on surprise outside state.

But I think the spirit of your criticism is correct: you do really want to be able to type processes with intermediate inputs and outputs, in general, and Rust makes this hard (though not impossible: see Munksgaard's work on session types in Rust, for example). I would not have had a problem if the original article had decided that Rust's futures are unfit for its purposes, and it would have been an interesting case study in what exactly real-world code needs from the API; my complaint is just that they get categorized as a type of I/O, which couldn't be further from the truth.