/*
 * $Header$
 * $Revision: 1128 $
 * $Date: 2006-02-05 13:49:04 -0800 (Sun, 05 Feb 2006) $
 *
 * ====================================================================
 *
 * Copyright 2000-2002 bob mcwhirter & James Strachan.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * 
 *   * Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 * 
 *   * Neither the name of the Jaxen Project nor the names of its
 *     contributors may be used to endorse or promote products derived 
 *     from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * ====================================================================
 * This software consists of voluntary contributions made by many 
 * individuals on behalf of the Jaxen Project and was originally 
 * created by bob mcwhirter <bob@werken.com> and 
 * James Strachan <jstrachan@apache.org>.  For more information on the 
 * Jaxen Project, please see <http://www.jaxen.org/>.
 * 
 * $Id: Function.java 1128 2006-02-05 21:49:04Z elharo $
 */


package org.jaxen;

import java.util.List;

/** Interface for the extensible function framework.
 *
 *  <p>
 *  <strong>NOTE:</strong> This class is not typically used directly,
 *  but is exposed for writers of extended XPath packages.
 *  </p>
 *
 *  <p>
 *  Implementations of <code>Function</code> are functors
 *  which are used to evaluate a function-call within an
 *  XPath expression.  
 *  </p>
 *
 *  @see FunctionContext
 *
 *  @author <a href="mailto:bob@werken.com">bob mcwhirter</a>
 */
public interface Function
{
    /** Evaluate this function.
     *
     * @param context the context at the point in the
     *         expression when the function is called
     * @param args arguments provided to the function
     * 
     * @return the result of evaluating the function; a <code>List</code>
     *    (node-set), <code>Double</code>, <code>Boolean</code>, or
     *    <code>String</code>
     * 
     * @throws FunctionCallException if an XPath error occurs during evaluation;
     *     for instance, if the number or type of the arguments is incorrect
     */
    Object call(Context context,
                List args) throws FunctionCallException;
}
