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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: C vs Haskell for XML parsing
Date: Wed, 30 Aug 2023 21:09:06 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>
>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>
>>> David Brown <david.brown@hesbynett.no> writes:
>>> [...]
>>>
>>>> Being able to accept $ in identifiers is a convenient extension.
>>>
>>> Quibble: $ in identifiers is not an extension as specified in section 4
>>> of the standard.  Starting in C99, the set of characters accepted in
>>> identifiers is implementation-defined.  (I'm not sure what difference
>>> that makes.)
>>
>> In Annex J, J.5.2 gives adding $ to the set of characters that
>> can appear in identifiers as an example of a common extension.
>
> C90 says the same thing in its Annex G.  Looks like they didn't update
> it when C99 updated the syntax for an identifier.

Certainly it's true that this passage wasn't changed.  That doesn't
mean it wasn't reviewed;  it may have been deliberately left in.
There have been lots of opportunities to change it, and it hasn't
been changed yet.

> (Though I suppose an
> implementation could accept $ in identifiers either as an extension or
> as an "other implementation-defined character".)

Yes, no question about it.  Furthermore implementors might make one
choice or the other, depending on how they think of the character(s)
in question.  For myself, I expect I would naturally think of adding
characters from another alphabet in the implementation-defined
sense, but think of adding $ in the extension sense.  Having both
options has some value, in terms of conveying mindset.