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/*
 * $Id: Exists.java,v 1.3 2007/05/20 18:00:44 obecker Exp $
 * 
 * The contents of this file are subject to the Mozilla Public License 
 * Version 1.1 (the "License"); you may not use this file except in 
 * compliance with the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the 
 * License.
 *
 * The Original Code is: this file
 *
 * The Initial Developer of the Original Code is Oliver Becker.
 *
 * Portions created by  ______________________ 
 * are Copyright (C) ______ _______________________. 
 * All Rights Reserved.
 *
 * Contributor(s): ______________________________________. 
 */

package net.sf.joost.stx.function;

import net.sf.joost.grammar.EvalException;
import net.sf.joost.grammar.Tree;
import net.sf.joost.stx.Context;
import net.sf.joost.stx.Value;
import net.sf.joost.stx.function.FunctionFactory.Instance;

import org.xml.sax.SAXException;

/**
 * The exists function.

 * Returns false if the argument is the empty sequence and
 * true otherwise.
 * 
 * @see  fn:exists in
 *      "XQuery 1.0 and XPath 2.0 Functions and Operators"
 * @version $Revision: 1.3 $ $Date: 2007/05/20 18:00:44 $
 * @author Oliver Becker
 */
final public class Exists implements Instance
{
   /** @return 1 */
   public int getMinParCount() { return 1; }
   /** @return 1 */
   public int getMaxParCount() { return 1; }
   /** @return "exists" */
   public String getName() { return FunctionFactory.FNSP + "exists"; }

   /** @return true */
   public boolean isConstant() { return true; }

   public Value evaluate(Context context, int top, Tree args)
      throws SAXException, EvalException
   {
      Value v = args.evaluate(context, top);
      return Value.getBoolean(v.type != Value.EMPTY);
   }
}