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1   /*
2    * $Header$
3    * $Revision: 1128 $
4    * $Date: 2006-02-05 13:49:04 -0800 (Sun, 05 Feb 2006) $
5    *
6    * ====================================================================
7    *
8    * Copyright 2000-2002 bob mcwhirter & James Strachan.
9    * All rights reserved.
10   *
11   * Redistribution and use in source and binary forms, with or without
12   * modification, are permitted provided that the following conditions are
13   * met:
14   * 
15   *   * Redistributions of source code must retain the above copyright
16   *     notice, this list of conditions and the following disclaimer.
17   * 
18   *   * Redistributions in binary form must reproduce the above copyright
19   *     notice, this list of conditions and the following disclaimer in the
20   *     documentation and/or other materials provided with the distribution.
21   * 
22   *   * Neither the name of the Jaxen Project nor the names of its
23   *     contributors may be used to endorse or promote products derived 
24   *     from this software without specific prior written permission.
25   * 
26   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
27   * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
28   * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
29   * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
30   * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
31   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
32   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
33   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
34   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
35   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
36   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
37   *
38   * ====================================================================
39   * This software consists of voluntary contributions made by many 
40   * individuals on behalf of the Jaxen Project and was originally 
41   * created by bob mcwhirter <bob@werken.com> and 
42   * James Strachan <jstrachan@apache.org>.  For more information on the 
43   * Jaxen Project, please see <http://www.jaxen.org/>.
44   * 
45   * $Id: Function.java 1128 2006-02-05 21:49:04Z elharo $
46   */
47  
48  
49  package org.jaxen;
50  
51  import java.util.List;
52  
53  /** Interface for the extensible function framework.
54   *
55   *  <p>
56   *  <strong>NOTE:</strong> This class is not typically used directly,
57   *  but is exposed for writers of extended XPath packages.
58   *  </p>
59   *
60   *  <p>
61   *  Implementations of <code>Function</code> are functors
62   *  which are used to evaluate a function-call within an
63   *  XPath expression.  
64   *  </p>
65   *
66   *  @see FunctionContext
67   *
68   *  @author <a href="mailto:bob@werken.com">bob mcwhirter</a>
69   */
70  public interface Function
71  {
72      /** Evaluate this function.
73       *
74       * @param context the context at the point in the
75       *         expression when the function is called
76       * @param args arguments provided to the function
77       * 
78       * @return the result of evaluating the function; a <code>List</code>
79       *    (node-set), <code>Double</code>, <code>Boolean</code>, or
80       *    <code>String</code>
81       * 
82       * @throws FunctionCallException if an XPath error occurs during evaluation;
83       *     for instance, if the number or type of the arguments is incorrect
84       */
85      Object call(Context context,
86                  List args) throws FunctionCallException;
87  }