Re: pure-fns in byte-opt.el

[Philipp Stephani <p.stephani2@gmail.com>]

Am Sa., 25. Juli 2020 um 22:59 Uhr schrieb Stefan Monnier
<monnier@iro.umontreal.ca>:
>
> >> The above "definition" seems to allow that: based on looking at the code
> >> you should be able to assess whether it's safe to allow the compiler (or
> >> anything else for that matter) to precompute the call.
> > I wouldn't know how that should be possible without knowing how the
> > compiler operates (or what it "knows" or can know).
>
> Why would you need to know that?
> As mentioned between parentheses it's not specific to a compiler.
> Is it that you find "precompute" unclear?

Yes, but also referring to a compiler, whether the current
implementation or some abstract one. We should be able to define the
semantics of Emacs Lisp without referring to implementation details
such as byte compilation. The current manual already attempts to do
that, it's just not 100% complete and correct.

>
> > It relies on some (rather vague) terms about the compiler, such as
> > "precompute" and "know". What if we change the compiler significantly
> > so that it "knows" much more?
>
> Doesn't make a difference: it will just make it possible for the compiler
> to precompute more often, whereas what this flag says is "when the
> compiler is *able* to precompute the call, should it be *allowed* to do
> so".
>
>
>         Stefan
>