From: Barry Margolin <barmar@alum.mit.edu>
To: help-gnu-emacs@gnu.org
Subject: Re: Reverse pop, return value
Date: Tue, 17 Nov 2009 16:34:53 -0500 [thread overview]
Message-ID: <barmar-A68984.16345317112009@nothing.attdns.com> (raw)
In-Reply-To: 9af6462e-4a2e-4325-b11d-9d8a6c2686b5@r24g2000yqd.googlegroups.com
In article
<9af6462e-4a2e-4325-b11d-9d8a6c2686b5@r24g2000yqd.googlegroups.com>,
LanX <lanx.perl@googlemail.com> wrote:
> Thanx Lennart!
>
> Thats what I was looking for! 8)
>
> ---------------
> (defun rpop (LIST)
> "reverse pop"
> (prog1
> (car (last LIST))
> (nbutlast LIST 1)
> )
> )
> --------------
>
> bye
> rolf
As I mentioned in the "remove last element in a list" thread, this won't
work when the list gets down to 1 element. nbutlast works by changing
the cdr of the 2nd-to-last cons cell in the list to point to nil. But
if there's only 1 element, there's no 2nd-to-last cons cell to modify.
You need to assign to the original variable, and this can only be done
using a macro (that's why push and pop are macros).
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
next prev parent reply other threads:[~2009-11-17 21:34 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-17 13:11 Remove last element in a list Nordlöw
2009-11-17 14:20 ` LanX
2009-11-17 15:32 ` Reverse pop, return value LanX
2009-11-17 15:48 ` Lennart Borgman
2009-11-17 16:53 ` David Kastrup
2009-11-17 17:33 ` LanX
[not found] ` <mailman.10897.1258472938.2239.help-gnu-emacs@gnu.org>
2009-11-17 17:20 ` LanX
2009-11-17 21:34 ` Barry Margolin [this message]
2009-11-18 0:28 ` LanX
2009-11-19 13:41 ` Barry Margolin
2009-11-17 21:26 ` Remove last element in a list 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=barmar-A68984.16345317112009@nothing.attdns.com \
--to=barmar@alum.mit.edu \
--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.