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@lists.isocpp.org> 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@kernel.org>

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

--
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