From: Tino Calancha <f92capac@gmail.com>
To: 21782@debbugs.gnu.org
Cc: Artur Malabarba <bruce.connor.am@gmail.com>
Subject: bug#21782: 25.0.50; New functions nfront/front
Date: Fri, 30 Oct 2015 10:25:31 +0900 (JST) [thread overview]
Message-ID: <alpine.LRH.2.20.1510301017410.10242@calancha-ilc.kek.jp> (raw)
In-Reply-To: <CAAdUY-JKjfvQSXs4SqZK=6+A69H4b5g8GDiGvEmJoRURWUgWww@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 1670 bytes --]
> I think this is already available in core as seq-take, from the seq package.
Thank you, you are right. Indeed, I found seq-take very nice:
its more general because apply to sequences.
There is one small difference: seq-take has no optional arguments.
In addition, seq.el need to be loaded by the user. Yeah, not a big
deal, but IMO such fundamental operation on a list as nfront
implement, deserve to be available at the starting of the session.
Putting a dedicated function in subr.el we save to load many stuff from
seq.el that maybe we dont need.
I would like nfront/front would behave as nbutlast/butlast concerning
the N argument:
*) N nil giving same output as N = 1.
*) N <= 0 return the full list.
(I choose the name of the function to somehow reflect such symmetry).
I have modified my patch to accomplish such behaviour.
With the new patch
(let ((ltest '(1 2 3 4 5 6)))
(nbutlast ltest nil))
(1 2 3 4 5)
(let ((ltest '(1 2 3 4 5 6)))
(nfront ltest nil))
(1)
(require 'seq)
(let ((ltest '(1 2 3 4 5 6)))
(seq-take ltest nil)); error: second argument is not optional
(let ((ltest '(1 2 3 4 5 6)))
(nbutlast ltest 0))
(1 2 3 4 5 6)
(let ((ltest '(1 2 3 4 5 6)))
(nfront ltest 0))
(1 2 3 4 5 6)
(let ((ltest '(1 2 3 4 5 6)))
(seq-take ltest 0))
nil
(let ((ltest '(1 2 3 4 5 6)))
(nbutlast ltest -1))
(1 2 3 4 5 6)
(let ((ltest '(1 2 3 4 5 6)))
(nfront ltest -1))
(1 2 3 4 5 6)
(let ((ltest '(1 2 3 4 5 6)))
(seq-take ltest -1))
nil
(let ((ltest '(1 2 3 4 5 6)))
(nbutlast ltest 20))
nil
(let ((ltest '(1 2 3 4 5 6)))
(nfront ltest 20))
(1 2 3 4 5 6)
(let ((ltest '(1 2 3 4 5 6)))
(seq-take ltest 20))
(1 2 3 4 5 6)
[-- Attachment #2: Type: text/plain, Size: 1534 bytes --]
diff --git a/lisp/subr.el b/lisp/subr.el
index ea926ae..ef705eb 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -391,13 +391,15 @@ last
(defun butlast (list &optional n)
"Return a copy of LIST with the last N elements removed.
If N is omitted or nil, the last element is removed from the
-copy."
+copy.
+When N is <= 0 LIST is returned."
(if (and n (<= n 0)) list
(nbutlast (copy-sequence list) n)))
(defun nbutlast (list &optional n)
"Modifies LIST to remove the last N elements.
-If N is omitted or nil, remove the last element."
+If N is omitted or nil, remove the last element.
+When N is <= 0 LIST is returned unmodified."
(let ((m (length list)))
(or n (setq n 1))
(and (< n m)
@@ -405,6 +407,21 @@ nbutlast
(if (> n 0) (setcdr (nthcdr (- (1- m) n) list) nil))
list))))
+(defun front(list &optional n)
+ "Return a copy of LIST with just the first N elements.
+If is omitted or nil copy just the first element
+When N is <= 0 the full list is copied."
+ (if (and n (<= n 0)) list
+ (nfront (copy-sequence list) n)))
+
+(defun nfront(list &optional n)
+ "Modified LIST to remove all elements but the first N.
+If N is omitted or nil remove all but the first element
+When N is <= 0 LIST is returned unmodified."
+ (or n (setq n 1))
+ (if (<= n 0) list
+ (nreverse (last (nreverse list) n))))
+
(defun zerop (number)
"Return t if NUMBER is zero."
;; Used to be in C, but it's pointless since (= 0 n) is faster anyway because
next prev parent reply other threads:[~2015-10-30 1:25 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-29 9:57 bug#21782: 25.0.50; New functions nfront/front Tino Calancha
2015-10-29 15:25 ` Artur Malabarba
2015-10-30 1:25 ` Tino Calancha [this message]
2015-10-30 2:38 ` Michael Heerdegen
2015-10-30 2:53 ` Constantino Calancha
2015-10-30 9:45 ` Artur Malabarba
2015-10-30 10:10 ` Tino Calancha
2015-10-30 10:03 ` Nicolas Petton
2015-10-30 10:11 ` Tino Calancha
2015-10-30 14:09 ` Michael Heerdegen
2015-10-30 18:06 ` Tino Calancha
2015-10-30 2:10 ` Tino Calancha
2015-10-30 1:33 ` Richard Stallman
2015-10-30 1:41 ` Constantino Calancha
[not found] ` <mailman.1293.1446168906.7904.bug-gnu-emacs@gnu.org>
2015-10-31 22:44 ` Alan Mackenzie
2017-05-18 4:08 ` Tino Calancha
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=alpine.LRH.2.20.1510301017410.10242@calancha-ilc.kek.jp \
--to=f92capac@gmail.com \
--cc=21782@debbugs.gnu.org \
--cc=bruce.connor.am@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 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.