From: Tino Calancha <f92capac@gmail.com>
To: 21782@debbugs.gnu.org
Subject: bug#21782: 25.0.50; New functions nfront/front
Date: Thu, 29 Oct 2015 18:57:59 +0900 (JST) [thread overview]
Message-ID: <alpine.LRH.2.20.1510291852300.4771@calancha-ilc.kek.jp> (raw)
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In GNU Emacs 25.0.50.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.23)
of 2015-10-29
Repository revision: 07830c3d5c801d7d55622215b46ba692c6afa1d2
I found very useful to define one function returning:
(nreverse (last (nreverse list) N))
(for a given list and integer N)
Maybe its already defined somewhere, but i cannot find it.
Examples of the new function:
(let ((ltest '( 1 2 3 4 5 6)))
(nfront ltest 3))
(1 2 3)
(let ((ltest '( 1 2 3 4 5 6)))
(nfront ltest 1))
(1)
(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)))
(nfront ltest))
(1 2 3 4 5 6)
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diff --git a/lisp/subr.el b/lisp/subr.el
index ea926ae..976e4fd 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -405,6 +405,19 @@ 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 N is omitted or nil the full list is copied."
+(let ((m (length list)))
+ (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 the full list is copied."
+ (if (or (null n) (and n (<= 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 reply other threads:[~2015-10-29 9:57 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-29 9:57 Tino Calancha [this message]
2015-10-29 15:25 ` bug#21782: 25.0.50; New functions nfront/front Artur Malabarba
2015-10-30 1:25 ` Tino Calancha
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
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