Re: continuation passing in Emacs vs. JUST-THIS-ONE

[Jim Porter <jporterbugs@gmail.com>]

On 3/11/2023 4:53 AM, Thomas Koch wrote:
> TL;DR: (Why) is there no standard way for continuation passing style[1] ("event driven") programming in Emacs?

There is (sort of): generator.el. There's also 'eshell-do-eval', but 
that's not as useful for general purposes, and I hope to replace it with 
either generator.el or real threads at some point in the future.

It would probably be reasonable to add a more asynchronous-oriented way 
of working with generator.el's CPS machinery, but I think the bigger 
problem is just the time to fix existing code that's not doing the right 
thing. Even without an easy-to-use asynchronous programming interface, 
you could probably get pretty far in terms of real-world improvements 
with using timers. I imagine timers would be a lot clumsier than a 
"proper" async API, but they'd likely work well enough for a first pass.

In any case, working on this would likely be a big help for Emacs. One 
of the more-common things I see people wish for in Emacs is "threading". 
I think this is probably a mistaken wish (Emacs generally doesn't use 
enough CPU to saturate a core), but what they really want is for fewer 
operations that block for a long time. If it were easier to divide up 
long-running tasks into small chunks, that would go a long way towards 
solving these sorts of issues.

(In theory, you could even get real multithreading this way, if you 
could divide up your task in a way that Emacs could be sure some chunk 
can be offloaded onto another thread.)