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From: Drew Adams <drew.adams@oracle.com>
To: Michael Heerdegen <michael_heerdegen@web.de>, help-gnu-emacs@gnu.org
Subject: RE: alist-get in Emacs 24?
Date: Thu, 8 Oct 2015 08:53:55 -0700 (PDT)	[thread overview]
Message-ID: <fcc233e7-0e38-458c-8eaf-12efa985d8ed@default> (raw)
In-Reply-To: <87egh5g48f.fsf@web.de>

> Second, yes, you could modify the list structure, but this can't be
> done if the alist is empty, because the empty (a)list is not a cons.
> At least in this case, your setter would still have to receive a symbol.

I don't see it that way.  How is this different from defining
`delete' or any of the other structure potentially-modifying
functions?  None of those functions require you to pass a symbol
argument.  The only function I can think of offhand that does
that is `add-to-list'.  Its more common (and generally more useful)
cousins, `push' and `pushnew' don't do that.

Yes, with such (destructive) functions, if you have a variable
pointing to the list (empty or not), you do need to re-set it
to the result returned by the function.  But that's all, AFAIK.

As I said (examples):
 (setq THE-VAR (my-set-alist-value key alist value))
 (setq foo (delete 42 foo))



  reply	other threads:[~2015-10-08 15:53 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-02  6:32 alist-get in Emacs 24? Marcin Borkowski
2015-10-02  6:39 ` Dmitry Gutov
2015-10-02  6:54   ` Marcin Borkowski
2015-10-02  7:34 ` Michael Heerdegen
2015-10-02  8:49   ` Marcin Borkowski
2015-10-03  3:05     ` Michael Heerdegen
2015-10-02 13:37   ` Stefan Monnier
2015-10-07 19:15   ` Marcin Borkowski
2015-10-07 20:45     ` Drew Adams
2015-10-08  8:21     ` Michael Heerdegen
2015-10-08 15:53       ` Drew Adams [this message]
2015-10-08 16:14         ` Michael Heerdegen

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