org.armedbear.lisp.last Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of abcl Show documentation
Common Lisp implementation running on the JVM
There is a newer version: 1.9.2
/*
 * last.java
 *
 * Copyright (C) 2003-2006 Peter Graves
 * $Id$
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 * As a special exception, the copyright holders of this library give you
 * permission to link this library with independent modules to produce an
 * executable, regardless of the license terms of these independent
 * modules, and to copy and distribute the resulting executable under
 * terms of your choice, provided that you also meet, for each linked
 * independent module, the terms and conditions of the license of that
 * module.  An independent module is a module which is not derived from
 * or based on this library.  If you modify this library, you may extend
 * this exception to your version of the library, but you are not
 * obligated to do so.  If you do not wish to do so, delete this
 * exception statement from your version.
 */

package org.armedbear.lisp;

import static org.armedbear.lisp.Lisp.*;

// ### last list &optional n => tail
public final class last extends Primitive
{
  public last()
  {
    super("last", "list &optional n");
  }

  @Override
  public LispObject execute(LispObject arg)
  {
    if (arg == NIL)
      return NIL;
    if (arg instanceof Cons)
      {
        while (true)
          {
            LispObject cdr = ((Cons)arg).cdr;
            if (!(cdr instanceof Cons))
              return arg;
            arg = cdr;
          }
      }
    else
      return type_error(arg, Symbol.LIST);
  }

  @Override
  public LispObject execute(LispObject first, LispObject second)

  {
    LispObject list = checkList(first);
    if (second instanceof Fixnum)
      {
        int n = ((Fixnum)second).value;
        if (n >= 0) {
          if (list == NIL)
            return NIL;
          LispObject result = list;
          while (list instanceof Cons)
            {
              list = list.cdr();
              if (n-- <= 0)
                result = result.cdr();
            }
          return result;
        }
      }
    else if (second instanceof Bignum)
      {
        if (list == NIL)
          return NIL;
        LispObject n = second;
        LispObject result = list;
        while (list instanceof Cons)
          {
            list = list.cdr();
            if (!n.plusp())
              result = result.cdr();
            n = n.decr();
          }
        return result;
      }
    return type_error(second, Symbol.UNSIGNED_BYTE);
  }

  private static final Primitive LAST = new last();
}