source: trunk/j/src/org/armedbear/lisp/list-length.lisp @ 11297

Last change on this file since 11297 was 11297, checked in by ehuelsmann, 13 years ago

Set Id keyword for expansion.

  • Property svn:eol-style set to native
  • Property svn:keywords set to Id
File size: 1.1 KB
Line 
1;;; list-length.lisp
2;;;
3;;; Copyright (C) 2003-2006 Peter Graves
4;;; $Id: list-length.lisp 11297 2008-08-31 13:26:45Z ehuelsmann $
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 #:system)
21
22(defun list-length (list)
23  (do ((n 0 (+ n 2))
24       (y list (cddr y))
25       (z list (cdr z)))
26      (())
27    (when (endp y)
28      (return n))
29    (when (endp (cdr y))
30      (return (+ n 1)))
31    (when (and (eq y z) (> n 0))
32      (return nil))))
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