From: "Adam Sjøgren" <asjo@koldfront.dk>
To: emacs-devel@gnu.org
Subject: Add hints to documentation of car and cdr for (e)lisp newcomers - take 2
Date: Wed, 14 Jul 2021 17:05:24 +0200 [thread overview]
Message-ID: <8735shrl57.fsf@tullinup.koldfront.dk> (raw)
Ten years ago I was confused by the documentation of car and cdr:
,----
| (car LIST)
|
| Return the car of LIST. If arg is nil, return nil.
`----
,----
| (cdr LIST)
|
| Return the cdr of LIST. If arg is nil, return nil.
`----
Which is which?!?
And I suggested a (bogus) improvement¹ based on reading too much into
the four letters L I S and T in the descriptions excerpted above.
While trying to write some basic elisp recently, I again realized that I
had forgotten which of car and cdr is which.
Based on one of the replies to my previous documentation improvement
attempt, I saw that there might be a way to improve the documentation
for my newbie case, without introducing something that is factually
wrong.
How about:
,----
| (car '(a . b))
|
| Return a. If arg is nil, return nil.
`----
,----
| (cdr '(a . b))
|
| Return b. If arg is nil, return nil.
`----
?
This variant of the documentation contains more information: what part
of the cons cell is returned by either function.
Also it doesn't use the four letters L I S and T, which might lead
somebody who hasn't read and memorized the Lisp intro, like me, to think
that what car/cdr works on is actually a LIST.
What do you think?
Hm, I realize now that you can call car and cdr on things that don't
look like '(a . b), so maybe this suggestion is as bad as the old one.
Maybe I should just try to stick to the mnemonic that car comes before
cdr alphabetically.
Or what about:
,----
| (car LIST)
|
| Return the car of LIST, eg if LIST is '(a . b) return a. If arg is nil, return nil.
`----
,----
| (cdr LIST)
|
| Return the cdr of LIST, eg if LIST is '(a . b) return b. If arg is nil, return nil.
`----
Ducking,
Adam
¹ https://debbugs.gnu.org/cgi/bugreport.cgi?bug=9082
--
"You know, I *thought* earth's gravity felt Adam Sjøgren
exceptionally strong today." asjo@koldfront.dk
next reply other threads:[~2021-07-14 15:05 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-14 15:05 Adam Sjøgren [this message]
2021-07-14 15:36 ` Add hints to documentation of car and cdr for (e)lisp newcomers - take 2 Andreas Schwab
2021-07-14 15:48 ` tomas
2021-07-14 15:50 ` Eli Zaretskii
2021-07-14 16:03 ` Lars Ingebrigtsen
2021-07-14 16:13 ` Eli Zaretskii
2021-07-15 4:34 ` Lars Ingebrigtsen
2021-07-14 23:49 ` Stefan Kangas
2021-07-15 4:38 ` Lars Ingebrigtsen
2021-07-15 11:39 ` Stefan Kangas
2021-07-15 14:14 ` Eli Zaretskii
2021-07-15 15:02 ` Tim Cross
2021-07-15 15:41 ` Stefan Monnier
2021-07-15 15:21 ` Stefan Monnier
2021-07-15 15:26 ` Yuan Fu
2021-07-15 15:52 ` Eduardo Ochs
2021-07-15 15:44 ` Lars Ingebrigtsen
2021-07-15 15:57 ` Eli Zaretskii
2021-07-16 0:22 ` Stefan Monnier
2021-07-16 2:08 ` Jean-Christophe Helary
2021-07-16 13:22 ` Stefan Monnier
2021-07-16 14:38 ` Basil L. Contovounesios
2021-07-16 7:00 ` Eli Zaretskii
2021-07-15 15:53 ` Eli Zaretskii
2021-07-15 16:17 ` Jean-Christophe Helary
2021-07-15 16:30 ` Lars Ingebrigtsen
2021-07-15 16:57 ` Eli Zaretskii
2021-07-15 17:01 ` Lars Ingebrigtsen
2021-07-15 17:07 ` Eli Zaretskii
2021-07-15 20:54 ` Stefan Kangas
2021-07-15 21:11 ` Lars Ingebrigtsen
2021-07-14 16:37 ` [External] : " Drew Adams
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
List information: https://www.gnu.org/software/emacs/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=8735shrl57.fsf@tullinup.koldfront.dk \
--to=asjo@koldfront.dk \
--cc=emacs-devel@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 public inbox
https://git.savannah.gnu.org/cgit/emacs.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).