GNU bug report logs - #79998
31.0.50; cond*: cdr-safe seems not work but cdr-ignore can.

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: "Yue Yi" <include_yy <at> qq.com>
To: "Spencer Baugh via Bug reports for GNU Emacs,the Swiss army knife of text editors"
 <bug-gnu-emacs <at> gnu.org>
Subject: 31.0.50; cond*: cdr-safe seems not work but cdr-ignore can.
Date: Sat, 13 Dec 2025 19:51:08 +0800

Hello, Emacs maintainers,

In the docstring of match*, it says:

(cdr-safe PATTERN) matches PATTERN with lax checking of cdrs. That means
that ‘list' patterns do not examine the final cdr.

Based on my understanding, cdr-safe should match improper lists or
similar structures. For example:

(cond* ((match* (cdr-safe (list x y)) '(1 2 . 3)))) => nil

However, running this triggers a warning: Warning: Complex pattern
nested in constrained variable pattern

I found that using cdr-ignore, which appears in the implementation
source code, works as expected:

(cond* ((match* (cdr-ignore (list x y)) '(1 2 . 3)))) ;;=> t

I would like to ask: Is this a documentation error? Should the docstring
and other references (like the Info manual) be updated to replace
cdr-safe with cdr-ignore?

Regards.

Message #8 received at 79998 <at> debbugs.gnu.org (full text, mbox):

From: Sean Whitton <spwhitton <at> spwhitton.name>
To: 79998 <at> debbugs.gnu.org, rms <at> gnu.org
Cc: Yue Yi <include_yy <at> qq.com>
Subject: Re: bug#79998: 31.0.50; cond*: cdr-safe seems not work but
 cdr-ignore can.
Date: Mon, 15 Dec 2025 12:02:11 +0000

Hello,

On Sat 13 Dec 2025 at 07:51pm +08, Yue Yi wrote:

> In the docstring of match*, it says:
>
> (cdr-safe PATTERN) matches PATTERN with lax checking of cdrs. That means
> that ‘list' patterns do not examine the final cdr.
>
> Based on my understanding, cdr-safe should match improper lists or
> similar structures. For example:
>
> (cond* ((match* (cdr-safe (list x y)) '(1 2 . 3)))) => nil
>
> However, running this triggers a warning: Warning: Complex pattern
> nested in constrained variable pattern
>
> I found that using cdr-ignore, which appears in the implementation
> source code, works as expected:
>
> (cond* ((match* (cdr-ignore (list x y)) '(1 2 . 3)))) ;;=> t
>
> I would like to ask: Is this a documentation error? Should the docstring
> and other references (like the Info manual) be updated to replace
> cdr-safe with cdr-ignore?

Yes, it looks like Richard decided to rename cdr-safe to cdr-ignore but
missed updating the docstring.  I've looked in the mailing list archives
and didn't see anything to suggest otherwise.

Richard, would you mind confirming?  "cdr-safe" was a work-in-progress
name, and "cdr-ignore" was the name for this match* operator that you
went for in the end?

-- 
Sean Whitton

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