From: Paul Eggert <eggert@cs.ucla.edu>
To: Yuri Khan <yurivkhan@gmail.com>, galex-713@galex-713.eu
Cc: Stefan Monnier <monnier@iro.umontreal.ca>,
Emacs developers <emacs-devel@gnu.org>
Subject: Re: Why is there no `until' in elisp?
Date: Wed, 17 Oct 2018 10:50:34 -0700 [thread overview]
Message-ID: <86294998-2c96-a1be-6a83-2e34b7fa6046@cs.ucla.edu> (raw)
In-Reply-To: <CAP_d_8V6EgbbTvzeNjKTJEHXW24yy-hUu==qCuTqR27zMpwXjQ@mail.gmail.com>
On 10/17/18 2:46 AM, Yuri Khan wrote:
> + Pascal has ‘repeat’/‘until’ (a termination post-condition loop), and
> it was my first association for the name ‘until’.
Pascal did it right, for a reason I haven't seen mentioned in this
thread. The natural tendency when reading a conditional is to assume
that the condition will be true in the code that immediately follows the
text of the condition. This works for (if C S) and (while C S), and it
also works for Pascal's 'repeat S1 until C; S2' where C is true just
before S2 is executed. It does not work for the confusing C syntax 'do
S1 while (C); S2' where C is false just before S2 is executed. It also
does not work for the proposed Elisp syntax (until C S), where C would
be false just before S is executed. Because of this elementary
psychological principle, the Elisp syntax for the proposed loop
construct should *not* be (until C S).
next prev parent reply other threads:[~2018-10-17 17:50 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-16 17:42 Why is there no `until' in elisp? Garreau, Alexandre
2018-10-16 19:16 ` Eric Abrahamsen
2018-10-16 19:31 ` Garreau, Alexandre
2018-10-16 20:23 ` Eric Abrahamsen
2018-10-16 23:00 ` Garreau, Alexandre
2018-10-19 15:28 ` Stefan Monnier
2018-10-16 21:28 ` Stefan Monnier
2018-10-17 0:12 ` Garreau, Alexandre
2018-10-17 2:04 ` Stefan Monnier
2018-10-17 9:14 ` Garreau, Alexandre
2018-10-17 15:06 ` Stefan Monnier
2018-10-17 16:51 ` Garreau, Alexandre
2018-10-19 15:34 ` Stefan Monnier
2018-10-19 18:08 ` Garreau, Alexandre
2018-10-17 8:04 ` Yuri Khan
2018-10-17 9:23 ` Garreau, Alexandre
2018-10-17 9:46 ` Yuri Khan
2018-10-17 11:06 ` Garreau, Alexandre
2018-10-17 17:50 ` Paul Eggert [this message]
2018-10-17 21:15 ` Garreau, Alexandre
2018-10-17 21:35 ` Paul Eggert
2018-10-17 21:49 ` Garreau, Alexandre
2018-10-17 22:33 ` Paul Eggert
2018-10-17 22:54 ` Garreau, Alexandre
2018-10-17 12:41 ` Elias Mårtenson
2018-10-17 15:03 ` Stefan Monnier
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=86294998-2c96-a1be-6a83-2e34b7fa6046@cs.ucla.edu \
--to=eggert@cs.ucla.edu \
--cc=emacs-devel@gnu.org \
--cc=galex-713@galex-713.eu \
--cc=monnier@iro.umontreal.ca \
--cc=yurivkhan@gmail.com \
/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).