From: Jean-Christophe Helary <brandelune@gmail.com>
To: help-gnu-emacs <help-gnu-emacs@gnu.org>
Subject: Re: using setq to create lists based on other lists...
Date: Mon, 3 Dec 2018 02:21:05 +0900 [thread overview]
Message-ID: <D0716D63-5297-4377-A867-318878FED74B@gmail.com> (raw)
In-Reply-To: <jwvlg57j2nj.fsf-monnier+gmane.emacs.help@gnu.org>
Thank you for the comments :)
> You're using `setq` on vars you haven't declared/defined yet!
The Introduction doesn't even mention that...
> I recommend you put `-*- lexical-binding:t -*-` somewhere on the first
> line of your file, and that you `M-x byte-compile RET` your file so
> Emacs can help you catch some of those issues.
I will.
> Better write this as (setf (nth 3 myDateLastMonth) myDay)
No reference to setf in the Introduction, and it's buried under tons of reference in the Reference...
Thank you again. Now I think there really is too much of a gap between the Introduction and the Reference. The exchange today kind of confirms that there is a need to overhaul the documentation so as to get beginners to produce better code...
Jean-Christophe
> On Dec 3, 2018, at 2:02, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
>
>> I see. Eventually I used copy-tree instead to initialize the new lists and
>> then modified them separately with setcar.
>
> So you're back to using `setcar` :-(
>
>> Just out of curiosity, let me post what I did. There are probably
>> better ways to do it, but that's the best I could come up with
>> today. I'd love to be able to think in terms closer to what elisp
>> allows though.
>
> Those date/time thingies are indeed rather annoying to construct.
> copy-sequence + in-place modification is probably the best you can
> use, indeed :-(
>
>> (setq now (decode-time (float-time))
>> myDateLastMonth (copy-tree now)
>> myDateThisMonth (copy-tree now)
>> myDateNextMonth (copy-tree now)
>> now (encode-time now 'integer))
>
> You're using `setq` on vars you haven't declared/defined yet!
> And theses aren't "trees" but lists/sequences, so better use
> `copy-sequence` which is also more efficient:
>
> (let* ((decoded-now (decode-time (float-time)))
> (myDateLastMonth (copy-tree now))
> (myDateThisMonth (copy-tree now))
> (myDateNextMonth (copy-tree now))
> (encoded-now (encode-time now 'integer)))
>
> I recommend you put `-*- lexical-binding:t -*-` somewhere on the first
> line of your file, and that you `M-x byte-compile RET` your file so
> Emacs can help you catch some of those issues.
>
>> ;; create the data for last month
>> (setcar (cdr (cdr (cdr myDateLastMonth))) myDay)
>
> Better write this as (setf (nth 3 myDateLastMonth) myDay)
> It's bad enough that the fields aren't named so you have to refer to
> them by position, but having to count `cdr`s is really annoying IMO.
>
>
> -- Stefan
>
>
Jean-Christophe Helary
-----------------------------------------------
http://mac4translators.blogspot.com @brandelune
next prev parent reply other threads:[~2018-12-02 17:21 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-02 10:53 using setq to create lists based on other lists Jean-Christophe Helary
2018-12-02 15:07 ` Stefan Monnier
2018-12-02 15:41 ` Jean-Christophe Helary
2018-12-02 16:05 ` Stefan Monnier
2018-12-02 16:23 ` Jean-Christophe Helary
2018-12-02 17:02 ` Stefan Monnier
2018-12-02 17:21 ` Jean-Christophe Helary [this message]
2018-12-02 19:11 ` Robert Thorpe
2018-12-02 23:44 ` Jean-Christophe Helary
[not found] ` <mailman.5028.1543765273.1284.help-gnu-emacs@gnu.org>
2018-12-03 13:43 ` Rusi
[not found] <mailman.5010.1543748027.1284.help-gnu-emacs@gnu.org>
2018-12-02 11:21 ` Barry Margolin
2018-12-02 11:51 ` Stephen Berman
2018-12-02 12:22 ` Jean-Christophe Helary
2018-12-02 13:08 ` Stephen Berman
2018-12-02 13:28 ` Jean-Christophe Helary
2018-12-02 14:40 ` Michael Heerdegen
2018-12-02 15:34 ` Jean-Christophe Helary
2018-12-02 15:44 ` Michael Heerdegen
2018-12-02 15:57 ` Jean-Christophe Helary
2018-12-02 15:00 ` Stephen Berman
2018-12-02 15:30 ` Jean-Christophe Helary
[not found] ` <mailman.5026.1543764670.1284.help-gnu-emacs@gnu.org>
2018-12-04 9:00 ` Barry Margolin
2018-12-02 12:03 ` Jean-Christophe Helary
[not found] <mailman.5042.1543777897.1284.help-gnu-emacs@gnu.org>
2018-12-04 9:04 ` Barry Margolin
[not found] ` <(message>
[not found] ` <from>
[not found] ` <Barry>
[not found] ` <Margolin>
[not found] ` <on>
[not found] ` <Tue>
[not found] ` <04>
[not found] ` <Dec>
[not found] ` <2018>
[not found] ` <04:04:52>
2018-12-04 13:56 ` Stefan Monnier
2018-12-05 1:07 ` Robert Thorpe
2018-12-05 2:32 ` Drew Adams
2018-12-05 6:45 ` Jean-Christophe Helary
2018-12-05 8:00 ` Marcin Borkowski
2018-12-05 8:11 ` Jean-Christophe Helary
2018-12-05 14:57 ` Drew Adams
[not found] ` <mailman.5218.1544021892.1284.help-gnu-emacs@gnu.org>
2018-12-05 16:59 ` Barry Margolin
[not found] ` <mailman.5186.1543978155.1284.help-gnu-emacs@gnu.org>
2018-12-05 16:50 ` Barry Margolin
[not found] ` <mailman.5145.1543931778.1284.help-gnu-emacs@gnu.org>
2018-12-05 16:47 ` Barry Margolin
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