Re: Emacs 30.0 warning from `cl-pushnew' and `memql'

[Emanuel Berg]

Stefan Monnier via Users list for the GNU Emacs text editor wrote:

>> (let ((lst '()))
>>   (cl-pushnew "a" lst)
>>   (cl-pushnew "a" lst)
>>   lst) ; ("a" "a")
>
> It may sometimes return ("a" "a") but it may also return
> ("a"). Case in point, I think it will do the first when
> interpreted and the second when compiled.

What's the deal with all that, can it be explained easily?

Why is it different?

That's not a good thing, right? I always thought of compiled
as just faster in execution, but computes faster ...

The compiler has some optimization scheme with recurring data
in space and time so the same data ends up at the same place
so is just pushed once?

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