GNU bug report logs - #50136
28.0.50; A problem with rx-let expansion

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Message #14 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: bug-gnu-emacs <at> gnu.org, Stefan Monnier <monnier <at> iro.umontreal.ca>
Subject: Re: 28.0.50; A problem with rx-let expansion
Date: Fri, 20 Aug 2021 19:21:20 +0200

Mattias Engdegård <mattiase <at> acm.org> writes:

> > AFAIU, the current approach doesn't allow to extend this with an
> > optional CHARS argument to specify with chars are allowed "in between"
> > (instead of "any").  The "&optional" keyword makes it barf.
>
> That's right. What would be the preferred semantics? For example, what
> value would you expect an absent optional parameter to take?

I guess it's not very useful for the current mechanism.  With a
macro-like thing, the expansion would just not use the value if it's nil.  The
expander would check whether the argument was provided.

> Actually it's the rx `eval` form that you are looking for if you want
> arbitrary compile-time computation. `regexp` and `literal` are
> explicitly made for run-time expressions.

Yes, I think you are right.


Michael.

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