GNU bug report logs - #72434
[PATCH] Print list-ending comma/backquote forms specially

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To reply to this bug, email your comments to 72434 AT debbugs.gnu.org.

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

From: Thuna <thuna.cing <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: [PATCH] Print list-ending comma/backquote forms specially
Date: Sat, 03 Aug 2024 03:31:28 +0200

[Message part 1 (text/plain, inline)]

(This patch follows from 72334, but that patch is not necessary for this
one to work.)

Currently something like the following (unevaluated) form:
  `(foo bar . ,baz)
prints as
  `(foo bar \, baz)
which, while technically accurate, is not helpful.  This comes up quite
often in pcase forms where a pattern like `(,head . ,_) is extremely
common.

This patch fixes that, such that if the tail of a list is a proper list
of two elements whose car is a backquote, comma, or comma-at (so ,foo
,@foo and `foo), and print-quoted is non-nil, the printed text will be
in the first form above.

Better ways to implement this are likely possible; this was simply the
easiest and quickest one.  Feel free to change the patch as needed.

[0001-Print-list-terminating-backquote-and-comma-forms-spe.patch (text/x-patch, attachment)]

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

From: Thuna <thuna.cing <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#72434: [PATCH] Print list-ending comma/backquote forms
 specially
Date: Sat, 03 Aug 2024 03:44:30 +0200

> (This patch follows from 72334, but that patch is not necessary for this
> one to work.)

Actually, that is incorrect...-ish.  The specific problem happens when
you encounter a comma or comma-at while not inside a backquote.  With
72334 this is not a problem, but without it you end up with the
(unevaluated) form
  (foo bar . ,baz)
printed as
  (foo bar . (\, baz))
which is obviously not ideal.

It /should/ be possible to lightly change the patch to have it work, by
checking `new_backquote_output' in case the car is a comma or a comma-at
but honestly I would just rather 72334 be pushed instead.

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