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Re: [wg14/wg21 liaison] (SC22WG14.19303) adding punctuator tokens

From: Jens Gustedt <jens.gustedt_at_[hidden]>
Date: Sat, 17 Apr 2021 11:36:23 +0200

on Sat, 17 Apr 2021 10:02:15 +0200 you (Jens Maurer
<Jens.Maurer_at_[hidden]>) wrote:

> On 17/04/2021 09.04, Jens Gustedt via Liaison wrote:
> > on Fri, 16 Apr 2021 17:11:12 -0400 you (Steve Downey
> > <sdowney_at_[hidden]>) wrote:
> >> There were some grammar changes just to fix some problems with
> >> pp-tokens, making sure that UCNs always were, and dealing with
> >> pp-numbers that don't turn out to be numbers.
> >
> > That worries me a bit more. I would be good if that would converge
> > to a common treatement in C and C++. I don't think that pp-numbers
> > in C ever caused serious problems. They just survive for later
> > translation phases and if they are not appropriate, the problem is
> > handled there.
> The paper is here:
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1949r6.html
> The pp-number change in particular is just applying the new
> UAX#31-based lexing grammar non-terminals to these. Nothing to see,
> I believe.

ah, ok. So I guess the intent of this change is to allow such letters
in application defined number and string suffixes? That would be
reasonable also to have for C, I think.

> Note that the lexing grammar presented here will need to change again
> once C++ switches to a "model C" approach (no early transformation
> of extended characters into UCNs)
> http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2021/p2314r1.html

That convinces me even more that this might be a good point in time to
start sharing a common specification for lexing and preprocessing.

I personally would for example not mind if by such a thing we would
import some punctuator tokens into C for which we don't have use yet
(as would have been for `::` if we hadn't adopted attributes) as long
as they don't conflict with the existing grammar. And also to extend
the preprocessor string and character literals should not conflict
too much with C's grammar.


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Received on 2021-04-17 04:36:31