From: Tino Calancha <f92capac@gmail.com>
To: 21782@debbugs.gnu.org
Cc: "C. Calancha" <f92capac@gmail.com>
Subject: bug#21782: 25.0.50; New functions nfront/front
Date: Fri, 30 Oct 2015 11:10:47 +0900 (JST) [thread overview]
Message-ID: <alpine.LRH.2.20.1510301107320.23447@calancha-ilc.kek.jp> (raw)
In-Reply-To: <CAAdUY-JKjfvQSXs4SqZK=6+A69H4b5g8GDiGvEmJoRURWUgWww@mail.gmail.com>
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The new patch has more sense to me.
I correct my previous wish about the func. behaviour with respect N:
*) N nil give same output as N = 1.
*) N <= 0 return nil.
(let ((ltest '(1 2 3 4 5 6)))
(nfront ltest 0))
nil
(let ((ltest '(1 2 3 4 5 6)))
(nfront ltest -1))
nil
(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)
(let ((ltest '(1 2 3 4 5 6)))
(nfront ltest 100))
(1 2 3 4 5 6)
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diff --git a/lisp/subr.el b/lisp/subr.el
index ea926ae..cde4006 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 +407,20 @@ 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 copy just the first element
+When N is <= 0 return nil."
+(if (or (null n) (> n 0))
+ (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 return nil."
+ (or n (setq n 1))
+ (if (> n 0) (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 2:10 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
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 [this message]
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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