Re: Lua 5.4 supports yield from __close, but fails with coroutine.close

[Jan Behrens <jbe-mlist@...>]

On Mon, 18 Sep 2023 14:09:36 -0700
Gé Weijers <ge@weijers.org> wrote:

> On Sun, Sep 17, 2023 at 3:56 AM Jan Behrens <jbe-mlist@magnetkern.de> wrote:
> 
> >
> > Is this a bug that could/should be fixed?
> >
> 
> I don't think this is even a bug, when you yield there has to be a call to
> 'resume' that receives the values yielded, and there isn't any.

Oh, you are right, I missed this.

> You could
> potentially return the values from coroutine.close but that would mean that
> coroutine.close could not 'close' the coroutine because it may have to
> yield potentially multiple times through the cleanup process.
> 
> I have trouble thinking of a use case for this to begin with.

Use case is implementing something like an effect system for Lua, see
<https://koka-lang.github.io/koka/doc/book.html> where causing an
effect is implemented by yielding in Lua. I wanted to use the __close
mechanism to implement something like Koka's "finally"
<https://koka-lang.github.io/koka/doc/std_core_hnd.html#finally>.
However, I need to be able to yield from within a "final handler"
because it needs to cause effects (handled by more outer layers).

In my use-case, an unhandled yield will cause another yield in the
outer coroutine; which is why I didn't notice that my example posted
here can't work.

I will think further about my problem.

> 
> -- 
> Gé

Thanks a lot for your feedback!

Regards,
Jan Behrens