source: trunk/j/src/org/armedbear/lisp/butlast.lisp @ 9266

Last change on this file since 9266 was 3829, checked in by piso, 18 years ago

Verify that N is a non-negative integer.

File size: 1.8 KB
Line 
1;;; butlast.lisp
2;;;
3;;; Copyright (C) 2003 Peter Graves
4;;; $Id: butlast.lisp,v 1.2 2003-09-16 18:00:18 piso Exp $
5;;;
6;;; This program is free software; you can redistribute it and/or
7;;; modify it under the terms of the GNU General Public License
8;;; as published by the Free Software Foundation; either version 2
9;;; of the License, or (at your option) any later version.
10;;;
11;;; This program is distributed in the hope that it will be useful,
12;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
13;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14;;; GNU General Public License for more details.
15;;;
16;;; You should have received a copy of the GNU General Public License
17;;; along with this program; if not, write to the Free Software
18;;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
19
20(in-package "COMMON-LISP")
21
22(export '(butlast nbutlast))
23
24(defun butlast (list &optional (n 1))
25  (unless (and (listp list) (typep n '(integer 0)))
26    (error 'type-error))
27  (unless (null list)
28    (let ((length (do ((list list (cdr list))
29           (i 0 (1+ i)))
30                      ((atom list) (1- i)))))
31      (unless (< length n)
32  (do* ((top (cdr list) (cdr top))
33        (result (list (car list)))
34        (splice result)
35        (count length (1- count)))
36             ((= count n) result)
37    (setq splice (cdr (rplacd splice (list (car top))))))))))
38
39(defun nbutlast (list &optional (n 1))
40  (unless (and (listp list) (typep n '(integer 0)))
41    (error 'type-error))
42  (unless (null list)
43    (let ((length (do ((list list (cdr list))
44           (i 0 (1+ i)))
45                      ((atom list) (1- i)))))
46      (unless (< length n)
47  (do ((1st (cdr list) (cdr 1st))
48       (2nd list 1st)
49       (count length (1- count)))
50            ((= count n)
51             (rplacd 2nd ())
52             list))))))
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