From: pjb@informatimago.com (Pascal J. Bourguignon)
To: help-gnu-emacs@gnu.org
Subject: Re: Collecting in the opposite order in a CL loop
Date: Sat, 27 Feb 2010 12:50:22 +0100 [thread overview]
Message-ID: <87vddiaoe9.fsf@galatea.lan.informatimago.com> (raw)
In-Reply-To: m2mxyve3rx.fsf@gmail.com
Sean McAfee <eefacm@gmail.com> writes:
> pjb@informatimago.com (Pascal J. Bourguignon) writes:
>
>> Sean McAfee <eefacm@gmail.com> writes:
>>> (loop for x = num then (/ x 10) until (zerop x) with result = nil do
>>> (setq result (cons (mod x 10) result))
>>> finally return result)
>
>> Use push instead of setq cons.
>> Use truncate instead of / for integer division.
>> Use finally (return ...); finally return is ClTl2, not Common Lisp.
>
> Thanks for the tips. But what's the reason for the last two? They seem
> equivalent to me, aside from the latter forms having the small advantage
> of brevity over the former.
You expressed a desire to program in a more "common" lisp.
In CL (/ 13 10) --> 13/10, and in CL finally return is invalid.
>>> Is there an elegant way to build up a list "backwards" using the CL loop
>>> facility?
>
>> Notice that building this list backwards as you want it is wrong:
>>
>> 1234 --> (1 2 3 4)
>> 34 --> (3 4)
>>
>> with the most significant digits in the lowest indexes, you cannot use
>> the list of digits do to anything.
>
> Nothing except what I need it for. I want to transform my input text in
> chunks of a certain small unit, identified by a regexp, and to do so a
> variable number of units at a time, inserting a space between the
> groups. The basic outline of my code is as follows:
>
> (defun transform-text (arg)
> (interactive "p")
> (save-match-data
> (loop for count in (digits-of arg) do
> (loop repeat count do
> (search-forward-regexp "\\=\\s *\\(etc.etc.\\)")
> (replace-match (compute-replacement-text (match-string 1)))
> finally (insert " "))
> finally (backward-delete-char 1))))
>
> So an argument of 123 to this routine would mean "transform one unit,
> insert a space, transform two more units, add a space, and lastly
> transform three more units." I need the digits most-significant-first
> because that's the order I typed them in.
>
> Anyway, I like how the collect clause lets me accumulate a return value
> for the loop without having to declare one explicitly, and was hoping a
> similar construction might let me do the same in the correct order for
> this usage.
Well, the most elegant way is often to use a recursive function as I
showed. Since it is expected that interactive user input won't overflow
the stack, there's no problem in using it.
--
__Pascal Bourguignon__
prev parent reply other threads:[~2010-02-27 11:50 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-27 1:35 Collecting in the opposite order in a CL loop Sean McAfee
2010-02-27 2:42 ` Pascal J. Bourguignon
2010-02-27 3:49 ` Sean McAfee
2010-02-27 11:50 ` Pascal J. Bourguignon [this message]
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
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87vddiaoe9.fsf@galatea.lan.informatimago.com \
--to=pjb@informatimago.com \
--cc=help-gnu-emacs@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 external index
https://git.savannah.gnu.org/cgit/emacs.git
https://git.savannah.gnu.org/cgit/emacs/org-mode.git
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.