[wahern]

A classic use case for coroutines is easily turning a push (callback) interface into a pull (return) interface. I'm sure many people have thought of using coroutines to handle GUI events this way. Certainly I have, and have even written some code along these lines in a macOS app primarily written in Lua (Yue as the GUI toolkit, along with my Lua I/O event library, cqueues, which I used to help tie into some event sources for which Yue lacked support; cqueues was designed to integrate with, rather than displace, other event loops).

However, GUI frameworks are a nightmare of criss-crossing events and state, and in practice callbacks are the least of your worries. In other domains callback interfaces often force you to scatter what would otherwise be highly localized logic, but it's the nature of GUI frameworks that your event logic will tend to be short, chunked, and scattered regardless, which is demonstrated by the toy examples. Yes, the async pattern turned event pushes into event pulls syntactically, but that's it--there was no real payoff.

I'm sure somebody will eventually go the distance with this approach. I won't dispute that the exercise would be a fun ride.