ISOCPP std-proposals List: Re: [std-proposals] alx-0014r6 - Refactor syntax of preprocessing directives

From: Brian Bi <bbi5291_at_[hidden]>
Date: Thu, 25 Sep 2025 12:46:16 -0400

If there's no change to behavior, and it's purely a refactoring of the
specification, then I don't expect WG21 to object, but the process to get
WG21's blessing is to bring it to the attention of SG22 so they can discuss
it. (I'm not sure how you do that from the C side; from the C++ side it is
done by publishing the paper in a mailing and setting the audience to SG22,
but presumably there's another process for papers that were originally sent
to the C committee.)

On Thu, Sep 25, 2025 at 12:38 PM Alejandro Colomar via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> Hi!
>
> I'm proposing some refactoring of the specification of the preprocessor
> in the C Committee (WG14). The committee wanted me to forward the
> proposal to the C++ Committee too, just to make sure that you're aware
> of it, and in case you have any reasons to disagree.
>
> I assume you'll agree, as the only syntactic difference between the C
> preprocessor and the C++ one is modules, and for the specification of
> modules, you did it exactly as I'm proposing now, so my expectation
> would be that WG21 is fine with this proposal.
>
> Essentially, it splits the huge Syntax clause from the preprocessor
> introduction, and puts each part under its own subclause.
>
> Please let me know, in any case. Find the proposal below (plain text).
>
>
> Have a lovely day!
> Alex
>
> ---
> Name
> alx-0014r6 - Refactor syntax of preprocessing directives
>
> Category
> Cosmetic refactor; readability; editorial;
>
> Authors
> Alejandro Colomar <alx_at_[hidden]>
>
> History
> <https://www.alejandro-colomar.es/src/alx/alx/wg14/alx-0014.git/>
>
> r4 (2025-08-29):
> - Split from alx-0014.
>
> r5 (2025-08-31):
> - Move alx-0014 to a separate proposal: alx-0065.
>
> r6 (2025-08-31):
> - Merge the split proposals into a single on with subsections.
>
> Principles
> - Keep the language small and simple
> - Facilitate interoperability
> - Codify existing practice to address evident deficiencies
>
> Rationale
> Editorial change. This moves text around for better
> organization and readability. No semantic changes. This makes
> it so that any future proposals to the preprocessor will be
> easier to apply.
>
> The proposal is split in subsections, separated by '---', for
> better readability.
>
> This proposal applies as is to the C++ latest draft, N5014, only
> changing section numbers and their titles.
>
> This change has prior art in C++, as they've done the same exact
> thing with their pp-import directive. I guess they haven't done
> it with the other directives for compatibility with us, so let's
> help them and do it everywhere.
>
> Interaction with other proposals
> This blocks alx-0003 ("Add directives #def and #enddef")
> This blocks alx-0013 ("Prohibit non-directives (other than ID
> directives)").
>
> ---
> Name
> alx-0014A - Refactor syntax of include directives
>
> Proposed wording
> Based on C N3550.
>
> 6.10.1 Preprocessing directives :: General (C++: 15.1 :: Preamble)
> @@ Syntax, p1 (C++: no 'Syntax' subtitle)
> control-line:
> - # include pp-tokens new-line
> + include-directive
> pp-import (C++ only)
> # embed pp-tokens new-line
> # define identifier replacement-list new-line
> # define identifier lparen identifier-list(opt)
> ) replacement-list new-line
> # define identifier lparen ... )
> replacement-list new-line
> # define identifier lparen identifier-list , ...
> ) replacement-list new-line
> # undef identifier new-line
> # line pp-tokens new-line
> # error pp-tokens(opt) new-line
> # warning pp-tokens(opt) new-line
> # pragma pp-tokens(opt) new-line
> # new-line
>
> 6.10.3 Source file inclusion (C++: 15.3)
> ## Add 'Syntax' before 'Constraints' (C++: No subtitles)
>
> @@ Syntax, new p after title
> +include-directive:
> + # include pp-tokens new-line
>
> ---
> Name
> alx-0014B - Refactor syntax of embed directives
>
> Proposed wording
> Based on N3550.
>
> 6.10.1 Preprocessing directives :: General
> @@ Syntax, p1
> control-line:
> # include pp-tokens new-line
> pp-import (C++ only)
> - # embed pp-tokens new-line
> + embed-directive
> # define identifier replacement-list new-line
> # define identifier lparen identifier-list(opt)
> ) replacement-list new-line
> # define identifier lparen ... )
> replacement-list new-line
> # define identifier lparen identifier-list , ...
> ) replacement-list new-line
> # undef identifier new-line
> # line pp-tokens new-line
> # error pp-tokens(opt) new-line
> # warning pp-tokens(opt) new-line
> # pragma pp-tokens(opt) new-line
> # new-line
>
> ...
>
> -pp-parameter:
> - pp-parameter-name pp-parameter-clause(opt)
> -
> -pp-parameter-name:
> - pp-standard-parameter
> - pp-prefixed-parameter
> -
> -pp-standard-parameter:
> - identifier
> -
> -pp-prefixed-parameter
> - identifier :: identifier
> -
> -pp-parameter-clause:
> - ( pp-balanced-token-sequence(opt) )
> -
> -pp-balanced-token-sequence:
> - pp-balanced-token
> - pp-balanced-token-sequence pp-balanced-token
> -
> -pp-balanced-token:
> - ( pp-balanced-token-sequence(opt) )
> - [ pp-balanced-token-sequence(opt) ]
> - { pp-balanced-token-sequence(opt) }
> - <r>any pp-token other than a parenthesis, a bracket, or a
> brace</r>
> -
> -embed-parameter-sequence:
> - pp-parameter
> - embed-parameter-sequence pp-parameter
>
> 6.10.4.1 Binary resource inclusion :: #embed preprocessing directive
> ## Add 'Syntax' before 'Description'
>
> @@ Syntax, new p after title
> +embed-directive:
> + # embed pp-tokens new-line
> +
> +pp-parameter:
> + pp-parameter-name pp-parameter-clause(opt)
> +
> +pp-parameter-name:
> + pp-standard-parameter
> + pp-prefixed-parameter
> +
> +pp-standard-parameter:
> + identifier
> +
> +pp-prefixed-parameter
> + identifier :: identifier
> +
> +pp-parameter-clause:
> + ( pp-balanced-token-sequence(opt) )
> +
> +pp-balanced-token-sequence:
> + pp-balanced-token
> + pp-balanced-token-sequence pp-balanced-token
> +
> +pp-balanced-token:
> + ( pp-balanced-token-sequence(opt) )
> + [ pp-balanced-token-sequence(opt) ]
> + { pp-balanced-token-sequence(opt) }
> + <r>any pp-token other than a parenthesis, a bracket, or a
> brace</r>
> +
> +embed-parameter-sequence:
> + pp-parameter
> + embed-parameter-sequence pp-parameter
>
> ---
> Name
> alx-0014C - Refactor syntax of macros
>
> Proposed wording
> Based on N3550.
>
> 6.10.1 Preprocessing directives :: General
> @@ Syntax, p1
> control-line:
> # include pp-tokens new-line
> # embed pp-tokens new-line
> - # define identifier replacement-list new-line
> - # define identifier lparen identifier-list(opt)
> ) replacement-list new-line
> - # define identifier lparen ... )
> replacement-list new-line
> - # define identifier lparen identifier-list , ...
> ) replacement-list new-line
> + define-directive
> - # undef identifier new-line
> + undef-directive
> # line pp-tokens new-line
> # error pp-tokens(opt) new-line
> # warning pp-tokens(opt) new-line
> # pragma pp-tokens(opt) new-line
> # new-line
>
> ...
>
> -lparen:
> - a ( character not immediately preceded by white
> space
> -
> -replacement-list:
> - pp-tokens(opt)
>
> ...
>
> -identifier-list:
> - identifier
> - identifier-list , identifier
>
> 6.10.5.1 Macro replacement :: General
> ## Add 'Syntax' before 'Constraints'
>
> @@ Syntax, new p after title
> +define-directive:
> + # define identifier replacement-list new-line
> + # define identifier lparen identifier-list(opt)
> ) replacement-list new-line
> + # define identifier lparen ... )
> replacement-list new-line
> + # define identifier lparen identifier-list , ...
> ) replacement-list new-line
> +
> +undef-directive:
> + # undef identifier new-line
> +
> +lparen:
> + a ( character not immediately preceded by white
> space
> +
> +replacement-list:
> + pp-tokens(opt)
> +
> +identifier-list:
> + identifier
> + identifier-list , identifier
>
> ---
> Name
> alx-0014D - Refactor syntax of conditional directives
>
> Proposed wording
> Based on N3550.
>
> 6.10.1 Preprocessing directives :: General
> @@ Syntax, p1
> -if-section:
> - if-group elif-groups(opt) else-group(opt) endif-line
> -
> -if-group:
> - # if constant-expression newline group(opt)
> - # ifdef identifier new-line group(opt)
> - # ifndef identifier new-line group(opt)
> -
> -elif-groups:
> - elif-group
> - elif-groups elif-group
> -
> -elif-group:
> - # elif constant-expression new-line group(opt)
> - # elifdef identifier new-line group(opt)
> - # elifndef identifier new-line group(opt)
> -
> -else-group:
> - # else new-line group(opt)
> -
> -endif-line:
> - # endif new-line
>
> 6.10.2 Conditional inclusion
> @@ Syntax, p1
> +if-section:
> + if-group elif-groups(opt) else-group(opt) endif-line
> +
> +if-group:
> + # if constant-expression newline group(opt)
> + # ifdef identifier new-line group(opt)
> + # ifndef identifier new-line group(opt)
> +
> +elif-groups:
> + elif-group
> + elif-groups elif-group
> +
> +elif-group:
> + # elif constant-expression new-line group(opt)
> + # elifdef identifier new-line group(opt)
> + # elifndef identifier new-line group(opt)
> +
> +else-group:
> + # else new-line group(opt)
> +
> +endif-line:
> + # endif new-line
> +
> ...
>
> ---
> Name
> alx-0014E - Refactor syntax of line directives
>
> Proposed wording
> Based on N3550.
>
> 6.10.1 Preprocessing directives :: General
> @@ Syntax, p1
> control-line:
> # include pp-tokens new-line
> # embed pp-tokens new-line
> # define identifier replacement-list new-line
> # define identifier lparen identifier-list(opt)
> ) replacement-list new-line
> # define identifier lparen ... )
> replacement-list new-line
> # define identifier lparen identifier-list , ...
> ) replacement-list new-line
> # undef identifier new-line
> - # line pp-tokens new-line
> + line-directive
> # error pp-tokens(opt) new-line
> # warning pp-tokens(opt) new-line
> # pragma pp-tokens(opt) new-line
> # new-line
>
> 6.10.6 Line control
> ## Add 'Syntax' before 'Constraints'
>
> @@ Syntax, new p after title
> +line-directive:
> + # line pp-tokens new-line
>
> ---
> Name
> alx-0014F - Refactor syntax of diagnostic directives
>
> Proposed wording
> Based on N3550.
>
> 6.10.1 Preprocessing directives :: General
> @@ Syntax, p1
> control-line:
> # include pp-tokens new-line
> # embed pp-tokens new-line
> # define identifier replacement-list new-line
> # define identifier lparen identifier-list(opt)
> ) replacement-list new-line
> # define identifier lparen ... )
> replacement-list new-line
> # define identifier lparen identifier-list , ...
> ) replacement-list new-line
> # undef identifier new-line
> # line pp-tokens new-line
> - # error pp-tokens(opt) new-line
> - # warning pp-tokens(opt) new-line
> + diagnostic-directive
> # pragma pp-tokens(opt) new-line
> # new-line
>
> 6.10.7 Diagnostic directives
> ## Add 'Syntax' before 'Constraints'
>
> @@ Syntax, new p after title
> +diagnostic-directive:
> + # error pp-tokens(opt) new-line
> + # warning pp-tokens(opt) new-line
>
> ---
> Name
> alx-0014G - Refactor syntax of pragma directives
>
> Proposed wording
> Based on N3550.
>
> 6.10.1 Preprocessing directives :: General
> @@ Syntax, p1
> control-line:
> # include pp-tokens new-line
> # embed pp-tokens new-line
> # define identifier replacement-list new-line
> # define identifier lparen identifier-list(opt)
> ) replacement-list new-line
> # define identifier lparen ... )
> replacement-list new-line
> # define identifier lparen identifier-list , ...
> ) replacement-list new-line
> # undef identifier new-line
> # line pp-tokens new-line
> # error pp-tokens(opt) new-line
> # warning pp-tokens(opt) new-line
> - # pragma pp-tokens(opt) new-line
> + pragma-directive
> # new-line
>
> 6.10.8 Pragma directive
> ## Add 'Syntax' before 'Constraints'
>
> @@ Syntax, new p after title
> +pragma-directive:
> + # pragma pp-tokens(opt) new-line
>
> ---
> Name
> alx-0014H - Refactor syntax of null directives
>
> Proposed wording
> Based on N3550.
>
> 6.10.1 Preprocessing directives :: General
> @@ Syntax, p1
> control-line:
> # include pp-tokens new-line
> # embed pp-tokens new-line
> # define identifier replacement-list new-line
> # define identifier lparen identifier-list(opt)
> ) replacement-list new-line
> # define identifier lparen ... )
> replacement-list new-line
> # define identifier lparen identifier-list , ...
> ) replacement-list new-line
> # undef identifier new-line
> # line pp-tokens new-line
> # error pp-tokens(opt) new-line
> # warning pp-tokens(opt) new-line
> # pragma pp-tokens(opt) new-line
> - # new-line
> + null-directive
>
>
> 6.10.9 Null directive
> ## Add 'Syntax' before 'Constraints'
>
> @@ Syntax, new p after title
> +null-directive:
> + # new-line
>
> --
> <https://www.alejandro-colomar.es>
> Use port 80 (that is, <...:80/>).
> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>

-- 
*Brian Bi*

Received on 2025-09-25 16:46:33