I found it all very confusing until I eventually wrote a little async task scheduler in Lua. Lua has an async / cooperative-coroutine API that is both very simple and easy to express meaningful coroutines with. The API is almost like a sort of system of safer gotos, but in practice it’s very much like Go channel receives, if waiting for a value from a channel was how you passed control to the producer side, and instead of a channel, the producer was just a function call that would return the next value every time you passed it control.

What’s interesting is that C++20 coroutines have very nearly the same API and semantics as Lua’s coroutines. Still haven’t taken the time to dive into that, but now that 23 is published and has working ranges, std::generator looks very promising since it’s kind of a lazy bridge between coroutines and ranges.