From: Stefan Kangas <stefan@marxist.se>
To: Lars Ingebrigtsen <larsi@gnus.org>
Cc: Robin Templeton <robin@terpri.org>,
19790@debbugs.gnu.org,
Michael Heerdegen <michael_heerdegen@web.de>
Subject: bug#19790: [PATCH] destructive splicing in backquote
Date: Sat, 14 Sep 2019 01:59:30 +0200 [thread overview]
Message-ID: <CADwFkmm-QOu_GiXmfLvmpEZ2C0hwFJTqkGKbj1HxuYeJo8thng@mail.gmail.com> (raw)
In-Reply-To: <87a90r35o9.fsf@panthera.terpri.org>
[-- Attachment #1: Type: text/plain, Size: 957 bytes --]
Lars Ingebrigtsen <larsi@gnus.org> writes:
> Robin Templeton <robin@terpri.org> writes:
>
>> Common Lisp and MACLISP define comma-dot syntax for destructive splicing
>> in backquote expressions. The Elisp reader reads ",.x" as "(\,\. x)"
>> (like ",@"), but the resulting forms are not processed by the backquote
>> library. A patch follows that adds CL-compatible comma-dot support.
>>
>> Originally reported by at Artur Malabarba in
>> <http://lists.gnu.org/archive/html/emacs-devel/2015-01/msg00624.html>.
>
> I think the conclusion to the discussion was that we do not want to
> support the ,. operation in Emacs Lisp.
>
> (setq .foo 1)
>
> `((,.foo))
> => (((\,\. foo)))
>
> So we should remove this feature completely, because that's obviously a
> bug...
Thanks to Michael Heerdegen's pointers, I could come up with a patch.
Would something like the attached do the job? It simply removes this
feature and adds a test.
Best regards,
Stefan Kangas
[-- Attachment #2: 0001-Remove-support-for-destructive-splicing-in-elisp.patch --]
[-- Type: text/x-patch, Size: 2584 bytes --]
From 6ec6c69242fdae2e8c3745e722aa6068c3366ba3 Mon Sep 17 00:00:00 2001
From: Stefan Kangas <stefankangas@gmail.com>
Date: Sat, 14 Sep 2019 01:49:23 +0200
Subject: [PATCH] Remove support for destructive splicing in elisp
* src/lread.c (read1): Don't handle destructive splicing in
backquote expressions (e.g. ",.<identifier>"). (Bug#19790)
(syms_of_lread): Remove Qcomma_dot.
* src/print.c (print_object): Don't check for Qcomma_dot.
* test/src/eval-tests.el
(eval-tests-19790-backquote-comma-dot-substitution): New test.
---
src/lread.c | 3 ---
src/print.c | 3 +--
test/src/eval-tests.el | 7 +++++++
3 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/src/lread.c b/src/lread.c
index 6ae7a0d8ba..0551376aa6 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -3307,8 +3307,6 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
if (ch == '@')
comma_type = Qcomma_at;
- else if (ch == '.')
- comma_type = Qcomma_dot;
else
{
if (ch >= 0) UNREAD (ch);
@@ -5080,7 +5078,6 @@ syms_of_lread (void)
DEFSYM (Qbackquote, "`");
DEFSYM (Qcomma, ",");
DEFSYM (Qcomma_at, ",@");
- DEFSYM (Qcomma_dot, ",.");
DEFSYM (Qinhibit_file_name_operation, "inhibit-file-name-operation");
DEFSYM (Qascii_character, "ascii-character");
diff --git a/src/print.c b/src/print.c
index 7c3da68fc9..bb013e282d 100644
--- a/src/print.c
+++ b/src/print.c
@@ -2086,8 +2086,7 @@ print_object (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag)
else if (print_quoted && CONSP (XCDR (obj)) && NILP (XCDR (XCDR (obj)))
&& new_backquote_output
&& (EQ (XCAR (obj), Qcomma)
- || EQ (XCAR (obj), Qcomma_at)
- || EQ (XCAR (obj), Qcomma_dot)))
+ || EQ (XCAR (obj), Qcomma_at)))
{
print_object (XCAR (obj), printcharfun, false);
new_backquote_output--;
diff --git a/test/src/eval-tests.el b/test/src/eval-tests.el
index 48295b81fa..7a8eae82cf 100644
--- a/test/src/eval-tests.el
+++ b/test/src/eval-tests.el
@@ -169,4 +169,11 @@ eval-tests-33014-redefine
"Remove the Lisp reference to the byte-compiled object."
(setf (symbol-function #'eval-tests-33014-func) nil))
+(defun eval-tests-19790-backquote-comma-dot-substitution ()
+ "Regression test for Bug#19790.
+Don't handle destructive splicing in backquote expressions (like
+in Common Lisp). Instead, make sure substitution in backquote
+expressions works for identifiers starting with period."
+ (should (equal (let ((.x 'identity)) (eval `(,.x 'ok))) 'ok)))
+
;;; eval-tests.el ends here
--
2.20.1
next prev parent reply other threads:[~2019-09-13 23:59 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-06 6:39 bug#19790: [PATCH] destructive splicing in backquote Robin Templeton
2015-02-06 15:29 ` Stefan Monnier
2015-02-07 18:51 ` Robin Templeton
2015-02-07 21:46 ` Robin Templeton
2015-02-08 19:23 ` Stefan Monnier
2015-02-08 19:38 ` Artur Malabarba
2015-02-09 3:10 ` Stefan Monnier
2015-02-09 13:03 ` Artur Malabarba
2016-02-23 11:08 ` Lars Ingebrigtsen
2019-06-25 17:59 ` Lars Ingebrigtsen
2019-06-25 22:52 ` Michael Heerdegen
2019-09-13 23:59 ` Stefan Kangas [this message]
2019-09-14 7:15 ` Eli Zaretskii
2019-09-14 12:31 ` Stefan Kangas
2019-09-14 13:30 ` Eli Zaretskii
2019-09-15 14:55 ` Stefan Kangas
2019-09-15 1:46 ` Stefan Monnier
2019-09-15 14:57 ` Stefan Kangas
2019-09-26 16:38 ` Stefan Kangas
2019-09-14 12:07 ` Lars Ingebrigtsen
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