/*
* KernelProlog Expanded - Pure Java based Prolog Engine
* Copyright (C) 1999 Paul Tarau (original KernelProlog)
* Copyright (C) 2009 Michiel Hendriks
*
* 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
package net.sf.kpex.builtins;
import net.sf.kpex.prolog.Cons;
import net.sf.kpex.prolog.FunBuiltin;
import net.sf.kpex.prolog.Prog;
/**
* returns the first element of a lazy list
*/
public class LazyHead extends FunBuiltin
{
public LazyHead()
{
super("lazy_head", 2);
}
@Override
public int exec(Prog p)
{
Cons L = (Cons) getArg(0);
return putArg(1, L.getHead(), p);
}
}