1 /*
2 * The contents of this file are subject to the BT "ZEUS" Open Source
3 * Licence (L77741), Version 1.0 (the "Licence"); you may not use this file
4 * except in compliance with the Licence. You may obtain a copy of the Licence
5 * from $ZEUS_INSTALL/licence.html or alternatively from
6 * http://www.labs.bt.com/projects/agents/zeus/licence.htm
7 *
8 * Except as stated in Clause 7 of the Licence, software distributed under the
9 * Licence is distributed WITHOUT WARRANTY OF ANY KIND, either express or
10 * implied. See the Licence for the specific language governing rights and
11 * limitations under the Licence.
12 *
13 * The Original Code is within the package zeus.*.
14 * The Initial Developer of the Original Code is British Telecommunications
15 * public limited company, whose registered office is at 81 Newgate Street,
16 * London, EC1A 7AJ, England. Portions created by British Telecommunications
17 * public limited company are Copyright 1996-9. All Rights Reserved.
18 *
19 * THIS NOTICE MUST BE INCLUDED ON ANY COPY OF THIS FILE
20 */
21
22
23
24 package zeus.concepts.fn;
25
26 import java.util.*;
27 import zeus.util.*;
28 import zeus.concepts.*;
29
30 public abstract class LogicalFn extends ValueFunction {
31 public static final int TRUE = 0;
32 public static final int FALSE = 1;
33 public static final int UNKNOWN = 2;
34
35 public LogicalFn(int type, int precedence) {
36 super(type,precedence);
37 }
38 public LogicalFn(int type) {
39 super(type,4);
40 }
41
42 public abstract int evaluate();
43
44 public int baseID() {
45 return BOOL;
46 }
47
48 ValueFunction unify(ValueFunction fn, Bindings b) {
49 int x;
50
51 switch( fn.getID() ) {
52 case ID:
53 case TYPE:
54 case INT:
55 case REAL:
56 case DATE:
57 case TIME:
58 case ARITH:
59 case VECT:
60 break;
61
62 // These have higher unification precedence
63 // case LVAR:
64 // case IMPLY:
65 // case ELSE:
66 // case CONSB:
67 // case FUNC:
68 // case METH:
69
70 case FIELD:
71 case AND:
72 case OR:
73 return new AndFn(evaluationFn(),fn);
74
75 case CONS:
76 if ( fn.isDeterminate() ) {
77 if (fn.baseID() != BOOL)
78 break;
79
80 switch( evaluate() ) {
81 case TRUE:
82 case FALSE:
83 return ConstraintFn.compare((ConstraintFn)fn,
84 (PrimitiveFn)evaluationFn());
85 case UNKNOWN:
86 return new AndFn(evaluationFn(),fn);
87 }
88 }
89 else
90 return new AndFn(evaluationFn(),fn);
91
92 case LOR:
93 case LAND:
94 case LNOT:
95 case COMP:
96 case BOOL:
97 x = ((LogicalFn)fn).evaluate();
98 switch( evaluate() ) {
99 case TRUE:
100 switch( x ) {
101 case TRUE:
102 return evaluationFn();
103 case FALSE:
104 return null;
105 case UNKNOWN:
106 return new AndFn(evaluationFn(),fn);
107 }
108 break;
109
110 case FALSE:
111 switch( x ) {
112 case TRUE:
113 return null;
114 case FALSE:
115 return evaluationFn();
116 case UNKNOWN:
117 return new AndFn(evaluationFn(),fn);
118 }
119 break;
120
121 case UNKNOWN:
122 return new AndFn(this,((LogicalFn)fn).evaluationFn());
123 }
124 break;
125
126 default:
127 break;
128 }
129 throw new IllegalArgumentException("Unification type clash " +
130 " attempting to unify \'" + fn + "\' with \'" + this + "\'");
131 }
132 }