From: Stefan Monnier <monnier@IRO.UMontreal.CA>
To: emacs-devel@gnu.org
Subject: Re: return
Date: Fri, 26 Nov 2010 09:59:51 -0500 [thread overview]
Message-ID: <jwvmxowywaq.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <m38w0gpimm.fsf@quimbies.gnus.org> (Lars Magne Ingebrigtsen's message of "Fri, 26 Nov 2010 09:57:21 +0100")
> While debugging and fixing stuff, I often find myself in the situation
> of adding more if/cond statements to a function and pushing the original
> body further in. I think this usually leads to less clear code.
If this is only "while debugging and fixing stuff", I don't think it's
a serious enough problem to warrant such a change. Note that my
preference to stick with the current situation in his respect is not
just out of inertia but also because I like a more functional style
of programming: usually/often you can find a formulation that's just as
elegant without the need for an early exit.
> This isn't the only use case, of course. A lot of functions in Emacs go
> through pretty awkward contortions to end loops when certain conditions
> occur.
I tend to agree that early exit from loops would be sometimes welcome.
Currently, people either use catch/throw, or contortions, or just decide
not to exit early. Also our while loops have no way to return a value,
so a `return' from a while loop can make the code *more* functional.
In functional programming language early exit constructs are rarely
needed because loops are written using recursion, so it's easy to exit
early: just don't recurse. One constructs which would improve the
situation (without adding early exits) would be to add an `until': it's
just like `while' except that the condition is reversed *and* that the
non-nil final condition is returned as value of the `until' expression.
Very often (until (progn foo bar) baz) works well. But I'd be OK with
adding a `return' from while loops: after all `while' loops are
naturally imperative, so such a `return' would not make things
less imperative.
Stefan
next prev parent reply other threads:[~2010-11-26 14:59 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-26 8:57 return Lars Magne Ingebrigtsen
2010-11-26 9:19 ` return Tassilo Horn
2010-12-04 2:36 ` return Fren Zeee
2010-12-04 3:04 ` Common vs Emacs Lisp (was: Re: return) Chad Brown
2010-12-04 19:48 ` Fren Zeee
2010-12-05 10:20 ` Chad Brown
2010-12-04 6:18 ` return Stephen J. Turnbull
2010-12-04 6:49 ` return Leo
2010-11-26 9:24 ` return Miles Bader
2010-11-26 9:36 ` return Lars Magne Ingebrigtsen
2010-11-26 9:54 ` return Miles Bader
2010-11-26 10:13 ` return Lars Magne Ingebrigtsen
2010-11-26 9:44 ` return Tassilo Horn
2010-11-26 14:59 ` Stefan Monnier [this message]
2010-11-26 15:45 ` return Lars Magne Ingebrigtsen
2010-11-26 18:40 ` return Stefan Monnier
2010-11-27 1:31 ` return Lars Magne Ingebrigtsen
2010-11-27 2:49 ` return Stefan Monnier
2010-11-27 3:06 ` return Lars Magne Ingebrigtsen
2010-12-03 18:41 ` return Chong Yidong
2010-12-03 18:43 ` return Miles Bader
2010-12-03 19:46 ` return Chong Yidong
2010-12-03 21:26 ` return Chong Yidong
2010-12-03 22:29 ` return Stefan Monnier
2010-12-03 23:00 ` return Chong Yidong
2010-12-04 1:35 ` return Stefan Monnier
2010-12-04 3:23 ` return Chong Yidong
2010-12-06 16:13 ` return Davis Herring
2010-12-06 17:15 ` return Chong Yidong
2010-12-03 22:44 ` return Chong Yidong
2010-12-04 9:22 ` return Helmut Eller
-- strict thread matches above, loose matches on Subject: below --
2010-11-26 23:01 return MON KEY
2010-12-05 23:55 Return MON KEY
2010-12-06 1:48 ` Return Stephen J. Turnbull
2010-12-06 5:50 ` Return MON KEY
2010-12-06 7:20 ` Return Stephen J. Turnbull
2010-12-06 9:00 ` Return David Kastrup
2010-12-06 19:11 ` Return Stefan Monnier
2010-12-06 19:09 ` Return Stefan Monnier
2010-12-06 19:19 ` Return Chong Yidong
2010-12-06 20:27 ` Return Stefan Monnier
2010-12-07 4:47 ` Return Miles Bader
2010-12-07 9:17 ` Return David Kastrup
2010-12-07 17:10 ` Return Stefan Monnier
2010-12-07 22:15 ` Return David Kastrup
2010-12-08 15:50 ` Return Fren Zeee
2010-12-09 22:38 ` Return Stefan Monnier
2010-12-10 1:41 ` Return Stephen J. Turnbull
2010-12-10 3:44 ` Return Stefan Monnier
2010-12-10 8:28 ` Return Stephen J. Turnbull
2010-12-23 5:39 ` Return Fren Zeee
2010-12-07 12:44 ` Return Stephen J. Turnbull
2010-12-07 14:38 ` Return David Kastrup
2010-12-07 16:14 ` Return Stephen J. Turnbull
2010-12-07 17:11 ` Return tomas
2010-12-07 2:42 ` Return MON KEY
2010-12-07 14:34 ` Return Stephen J. Turnbull
2010-12-07 15:54 ` Return David Kastrup
2010-12-07 16:30 ` Return Stephen J. Turnbull
2010-12-08 13:42 ` Return Richard Stallman
2010-12-10 7:42 ` Return Daniel Colascione
2010-12-07 22:55 ` Return MON KEY
2010-12-08 7:28 ` Return Stephen J. Turnbull
2010-12-08 18:11 ` Return MON KEY
2010-12-09 8:37 ` Return Stephen J. Turnbull
2010-12-07 23:21 ` Return Samuel Bronson
2010-12-08 8:06 ` Return Stephen J. Turnbull
2010-12-08 20:51 ` Return Samuel Bronson
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=jwvmxowywaq.fsf-monnier+emacs@gnu.org \
--to=monnier@iro.umontreal.ca \
--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).