From: Marcin Borkowski <mbork@wmi.amu.edu.pl>
To: Barry Margolin <barmar@alum.mit.edu>, help-gnu-emacs@gnu.org
Subject: Re: hash strangeness
Date: Tue, 04 Nov 2014 08:39:40 +0100 [thread overview]
Message-ID: <87ioive7nn.fsf@wmi.amu.edu.pl> (raw)
In-Reply-To: <0041d5f2-b328-4017-a748-ead21589f05e@default>
On 2014-11-04, at 04:04, Drew Adams wrote:
>> > I expect '(a b c) to create a new list with these symbols
>> > every time it runs.
>>
>> Why do you expect that?
>> '(a b c) is short for (quote (a b c)). quote returns its argument, it
>> doesn't make a copy of it.
>>
>> I'm sure somewhere in the Elisp programming manual it mentions that you
>> shouldn't use destructive functions on literal lists, like the Common
>> Lisp spec does.
>
> Here is one place: the Elisp manual, node `Rearrangement`. Search for
> "a common pitfall".
>
> https://www.gnu.org/software/emacs/manual/html_node/elisp/Rearrangement.html
And to see it yourself, execute (e.g. with C-x C-e) the following in
order:
(defun myfun () (setq myvar '(a b c)))
(myfun)
(symbol-value 'myvar)
(symbol-function 'myfun)
(nconc myvar '(1 2 3))
(symbol-value 'myvar)
(symbol-function 'myfun)
Hth,
--
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Adam Mickiewicz University
next prev parent reply other threads:[~2014-11-04 7:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-02 11:20 hash strangeness Tom
2014-11-02 12:09 ` Tom
2014-11-02 18:20 ` Thien-Thi Nguyen
2014-11-02 20:45 ` Tom
[not found] ` <mailman.12618.1414961152.1147.help-gnu-emacs@gnu.org>
2014-11-02 22:25 ` Pascal J. Bourguignon
2014-11-02 22:48 ` Barry Margolin
2014-11-03 21:29 ` Tom
2014-11-04 1:57 ` Robert Thorpe
2014-11-04 2:16 ` Michael Heerdegen
[not found] ` <<barmar-14233C.17480902112014@88-209-239-213.giganet.hu>
2014-11-04 3:04 ` Drew Adams
2014-11-04 7:39 ` Marcin Borkowski [this message]
[not found] <mailman.12577.1414927271.1147.help-gnu-emacs@gnu.org>
2014-11-02 18:43 ` Pascal J. Bourguignon
2014-11-02 20:48 ` Tom
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