01: package org.ofbiz.rules.engine;
02:
03: /**
04: * <p><b>Title:</b> Empty List
05: * <p><b>Description:</b> None
06: * <p>Copyright (c) 1999 Steven J. Metsker.
07: * <p>Copyright (c) 2001 The Open For Business Project - www.ofbiz.org
08: *
09: * <p>Permission is hereby granted, free of charge, to any person obtaining a
10: * copy of this software and associated documentation files (the "Software"),
11: * to deal in the Software without restriction, including without limitation
12: * the rights to use, copy, modify, merge, publish, distribute, sublicense,
13: * and/or sell copies of the Software, and to permit persons to whom the
14: * Software is furnished to do so, subject to the following conditions:
15: *
16: * <p>The above copyright notice and this permission notice shall be included
17: * in all copies or substantial portions of the Software.
18: *
19: * <p>THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
20: * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
21: * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
22: * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
23: * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT
24: * OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR
25: * THE USE OR OTHER DEALINGS IN THE SOFTWARE.
26: *
27: * <br>
28: * <p>The EmptyList is a list with no terms.
29: * <p>
30: * All lists except this one contain a head, which may be any
31: * term, and a tail, which is another list. This recursive
32: * defintion terminates with this singleton, the empty list.
33: *
34: * @author Steven J. Metsker
35: * @version 1.0
36: */
37: public class EmptyList extends Fact {
38:
39: /**
40: * Constructs the empty list singleton.
41: */
42: protected EmptyList() {
43: super (".");
44: }
45:
46: /**
47: * Return true, since an empty list is a list.
48: *
49: * @return true
50: */
51: public boolean isList() {
52: return true;
53: }
54:
55: /**
56: * Returns a string representation of this list as a part of
57: * another list. When the empty list represents itself as part
58: * of another list, it just returns "".
59: *
60: * @return an empty string
61: */
62: public String listTailString() {
63: return "";
64: }
65:
66: /**
67: * Returns a string representation of the empty list.
68: *
69: * @return a string representation of the empty list
70: */
71: public String toString() {
72: return "[]";
73: }
74: }
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