Second Draft: Coroutines

[Richard (Rikki) Andrew Cattermole]

On 23/01/2025 10:00 PM, Sebastiaan Koppe wrote:
> On Thursday, 12 December 2024 at 10:36:50 UTC, Richard (Rikki) Andrew 
> Cattermole wrote:
>> Stackless coroutines, is a way to enable asynchronous programming, for 
>> lesser skilled and less knowledgable people whilst offering efficient 
>> processing of events, safely.
>>
>> This version of the proposal has been rewritten to account for a lack 
>> of understanding on the separation of library code versus what the 
>> language is offering.
>>
>> And a few changes related to yielding. Yielding is no longer 
>> guaranteed to be implicit. You may explicitly yield using an ``await`` 
>> statement should you wish to. The library type must support implicit 
>> yielding if you wish to use it. Both may be used on the same type, it 
>> is entirely dependent upon the called methods attributes.
>>
>> Lastly, the changes have been made to simplify the descriptor to make 
>> the implementation within the compiler a little bit easier. It does 
>> mean that you as a library author have no way to know about the 
>> functions in the state machine (not that you could have done much with 
>> them).
>>
>> Current: https://gist.github.com/rikkimax/ 
>> fe2578e1dfbf66346201fd191db4bdd4/649a5a6cc68c4bfe9f5a62f746a3a90f6b4beaf4
>>
>> Latest: https://gist.github.com/rikkimax/fe2578e1dfbf66346201fd191db4bdd4
> 
> The design as presented isn't focused enough IMO. It lacks detail in 
> core areas and adds in too many (questionable) nice-to-have or day-two 
> features.
> 
> I believe the challenge with coroutines is twofold: 1) the code 
> transformations and 2) how/when to resume suspended coroutines. Then 
> there are secondary goals like extensibility/flexibility and eliding 
> allocations.
> 
> Additionally, the DIP has no reference to C++'s coroutine feature. I am 
> sure there is a ton written on the subject by users, implementors, 
> designers, etc.
> 
> A good starting point would be the official reference https:// 
> en.cppreference.com/w/cpp/language/coroutines

I didn't seen anything worth adding. So I haven't.

> as well as Lewis Baker's 
> blog: https://lewissbaker.github.io/2022/08/27/understanding-the- 
> compiler-transform (part 5 of 5), who is knee-deep in this stuff.

That article by Lewis Baker is pretty good at laying out how C++ does 
it, although it does hand waive some details away that I would be 
interested in.

It also confirms a couple of things for me.

1. Tieing the language to a specific library does not inherently make it 
simpler.
2. C++ has a more complex design, that does not offer anything above 
that of my proposal.

I'll add it to the references section, but not the prior work. This is 
not a copy C++ situation.