From: Francis Moreau <francis.moro@gmail.com>
To: help-gnu-emacs@gnu.org
Subject: Re: Basic questions about elisp
Date: Mon, 09 Nov 2009 22:04:41 +0100 [thread overview]
Message-ID: <m2k4xzo1ee.fsf@gmail.com> (raw)
In-Reply-To: 871vk99c08.fsf@galatea.local
pjb@informatimago.com (Pascal J. Bourguignon) writes:
> Francis Moreau <francis.moro@gmail.com> writes:
>
>> pjb@informatimago.com (Pascal J. Bourguignon) writes:
>>
>>> Francis Moreau <francis.moro@gmail.com> writes:
>>>>>> When I wrote '(2), I suppose the elisp interpreter to create a new
>>>>>> list.
>>>>>
>>>>> It does so, but at read time. Not execution time.
>>>>>
>>>>
>>>> Ah ok I see what you mean now.
>>>>
>>>> That's a pretty important point, is this part covered by the elisp info ?
>>>
>>> Yes.
>>>
>>
>> Sorry for being blind but I can't find the revelant section.
>>
>> Could you give me a pointer ?
>
> Well, there are several places where it's covered, but here is one
> where it's explicitely explained:
>
>
> (info "(elisp)Rearrangement")
>
>
> -- Function: nconc &rest lists
>
> [...]
>
> A common pitfall is to use a quoted constant list as a non-last
> argument to `nconc'. If you do this, your program will change
> each time you run it! Here is what happens:
>
> (defun add-foo (x) ; We want this function to add
> (nconc '(foo) x)) ; `foo' to the front of its arg.
>
> (symbol-function 'add-foo)
> => (lambda (x) (nconc (quote (foo)) x))
>
> (setq xx (add-foo '(1 2))) ; It seems to work.
> => (foo 1 2)
> (setq xy (add-foo '(3 4))) ; What happened?
> => (foo 1 2 3 4)
> (eq xx xy)
> => t
>
> (symbol-function 'add-foo)
> => (lambda (x) (nconc (quote (foo 1 2 3 4) x)))
ok that tells: "don't do that !" but it doesn't tell why not...
>
> Of course, it could be infered from:
> C-h f quote RET
> or:
> (info "(elisp)Quoting")
There's nothing here about a cons built by the Lisp Reader.
Thanks
--
Francis
next prev parent reply other threads:[~2009-11-09 21:04 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-05 11:13 Basic questions about elisp Francis Moreau
2009-11-05 11:50 ` Lennart Borgman
[not found] ` <mailman.10118.1257421858.2239.help-gnu-emacs@gnu.org>
2009-11-05 12:07 ` Francis Moreau
2009-11-05 12:44 ` Lennart Borgman
2009-11-05 12:59 ` David Kastrup
2009-11-05 14:25 ` Francis Moreau
2009-11-05 14:37 ` Pascal J. Bourguignon
2009-11-05 14:58 ` Pascal J. Bourguignon
2009-11-05 12:57 ` tomas
[not found] ` <mailman.10122.1257425638.2239.help-gnu-emacs@gnu.org>
2009-11-05 14:29 ` Francis Moreau
2009-11-05 14:41 ` Pascal J. Bourguignon
2009-11-05 15:06 ` David Kastrup
2009-11-06 16:03 ` Francis Moreau
2009-11-06 16:49 ` David Kastrup
2009-11-06 20:53 ` Francis Moreau
2009-11-06 21:18 ` Pascal J. Bourguignon
2009-11-07 14:49 ` Francis Moreau
2009-11-07 17:50 ` Pascal J. Bourguignon
2009-11-08 9:46 ` tomas
[not found] ` <mailman.10266.1257674088.2239.help-gnu-emacs@gnu.org>
2009-11-09 20:51 ` Francis Moreau
2009-11-08 15:18 ` Francis Moreau
2009-11-08 16:58 ` tomas
2009-11-08 17:12 ` Pascal J. Bourguignon
2009-11-09 21:04 ` Francis Moreau [this message]
2009-11-10 12:11 ` Joost Kremers
2009-11-10 14:16 ` Francis Moreau
2009-11-10 18:53 ` David Kastrup
2009-11-06 5:06 ` Barry Margolin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=m2k4xzo1ee.fsf@gmail.com \
--to=francis.moro@gmail.com \
--cc=help-gnu-emacs@gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this external index
https://git.savannah.gnu.org/cgit/emacs.git
https://git.savannah.gnu.org/cgit/emacs/org-mode.git
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.