Path: csiph.com!news.mixmin.net!eternal-september.org!reader01.eternal-september.org!.POSTED!not-for-mail From: Tim Rentsch Newsgroups: comp.lang.c Subject: Re: Cake - C23 to C99 transpiler Date: Thu, 15 Sep 2022 23:46:59 -0700 Organization: A noiseless patient Spider Lines: 74 Message-ID: <86v8pnlst8.fsf@linuxsc.com> References: <836c6515-87f5-42b2-98b0-8308173a9120n@googlegroups.com> <8735d39ou5.fsf@bsb.me.uk> <87leqv87t2.fsf@bsb.me.uk> <87fsh386ze.fsf@bsb.me.uk> <8735d380ta.fsf@bsb.me.uk> <87tu5ikivi.fsf@nosuchdomain.example.com> <86tu5am4a9.fsf@linuxsc.com> <87k065hm68.fsf@nosuchdomain.example.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: reader01.eternal-september.org; posting-host="4a0db673561e161ba81b81715d43a3e1"; logging-data="3799969"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18kfReeIlEnYDJlNm7nvu0FL2fb9UVBIuQ=" User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.4 (gnu/linux) Cancel-Lock: sha1:mGZq/zoCbusnAKVHDnE7lXoAseg= sha1:YKnmkujU3CESWF3lcjSwQYXFWl4= Xref: csiph.com comp.lang.c:167737 Keith Thompson writes: > Tim Rentsch writes: > >> Keith Thompson writes: >> >>> Bart writes: >>> [...] >>> >>>> Also, gcc gets away with allowing $ by default; tcc generally copies >>>> gcc in terms of how a compiler is invoked, so this surprisingly goes >>>> against that. >>> >>> gcc allowing $ in identifiers is a documented extension for most >>> targets, so it doesn't warn about them even with "-pedantic". One could >>> argue that this isn't necessarily an "extension", since "other >>> implementation-defined characters" are explicitly permitted by C11 >>> 6.4.2.1. >>> >>> Interestingly, the C23 draft doesn't have that wording. Instead, it >>> allows XID_Start and XID_Continue characters, so it expands the set of >>> characters that *all* implementations must support, >> >> I believe that conclusion is not correct. The C23 draft n3047 says >> this: >> >> An XID_Start character is an implementation-defined character >> whose corresponding code point in ISO/IEC 10646 has the >> XID_Start property. An XID_Continue character is an >> implementation-defined character whose corresponding code point >> in ISO/IEC 10646 has the XID_Continue property. >> >> The presence of the modifying adjective "implementation-defined" in >> both cases surely means, at the very least, that implementations >> are allowed to subset the Unicode-specified XID_Start/XID_Continue >> sets with regard to what characters are allowed in identifiers. > > You're right. I managed to miss the phrase "implementation-defined". > > So ISO/IEC 10646 defines which characters have the "XID_Start" property, > but an "XID_Start" character is a member of a C implementation-defined > subset of those characters. The terminology is a bit confusing, but I'm > not sure how I'd improve it. I did not consider the question of how to improve the wording in the ISO C standard. >>> but doesn't permit '$' (assuming '$' isn't in XID_Start or >>> XID_Continue). >> >> I'm not sure this statement is right either (and agreeing with the >> assumption that '$' is not in XID_Start or XID_Continue). To clarify my earlier statement, I am agreeing with (what I think is your) assumption that '$'s ISO/IEC 10646 code point does not have either the XID_Start property or the XID_Continue property. >> The >> Unicode reference documentation is so bad that I can't make out >> with any degree of certainty whether it allows various domains to >> extend the XID_Start/XID_Continue sets for the application in >> question. The presence of "implementation-defined" further muddies >> the waters. To be clear, neither am I saying that I think the >> statement is wrong; only that at present there is not enough >> information to be confident of either conclusion. > > If '$' can't be an XID_Start or XID_Continue character, then an attempt > to use '$' in an identifier is a syntax error. I don't see any wiggle > room there. The open question is whether '$' is, or can be, an > XID_Start or XID_Continue character. Yes, I believe these statements are consistent with the most natural reading of the current C23 draft (subject to a condition that the consistency property can be objectively quantified).