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-rw-r--r--OpenSim/Region/ScriptEngine/Shared/Api/Runtime/YieldProlog/Variable.cs196
1 files changed, 196 insertions, 0 deletions
diff --git a/OpenSim/Region/ScriptEngine/Shared/Api/Runtime/YieldProlog/Variable.cs b/OpenSim/Region/ScriptEngine/Shared/Api/Runtime/YieldProlog/Variable.cs
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1/*
2 * Copyright (C) 2007-2008, Jeff Thompson
3 *
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions are met:
8 *
9 * * Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * * Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 * * Neither the name of the copyright holder nor the names of its contributors
15 * may be used to endorse or promote products derived from this software
16 * without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
22 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
23 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
24 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
25 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
26 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
27 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
28 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31using System;
32using System.Collections;
33using System.Collections.Generic;
34
35namespace OpenSim.Region.ScriptEngine.Shared.YieldProlog
36{
37 public interface IUnifiable
38 {
39 IEnumerable<bool> unify(object arg);
40 void addUniqueVariables(List<Variable> variableSet);
41 object makeCopy(Variable.CopyStore copyStore);
42 bool termEqual(object term);
43 bool ground();
44 }
45
46 public class Variable : IUnifiable
47 {
48 // Use _isBound separate from _value so that it can be bound to any value,
49 // including null.
50 private bool _isBound = false;
51 private object _value;
52
53 public object getValue()
54 {
55 if (!_isBound)
56 return this;
57
58 object result = _value;
59 while (result is Variable)
60 {
61 if (!((Variable)result)._isBound)
62 return result;
63
64 // Keep following the Variable chain.
65 result = ((Variable)result)._value;
66 }
67
68 return result;
69 }
70
71 public IEnumerable<bool> unify(object arg)
72 {
73 if (!_isBound)
74 {
75 _value = YP.getValue(arg);
76 if (_value == this)
77 // We are unifying this unbound variable with itself, so leave it unbound.
78 yield return false;
79 else
80 {
81 _isBound = true;
82 try
83 {
84 yield return false;
85 }
86 finally
87 {
88 // Remove the binding.
89 _isBound = false;
90 }
91 }
92 }
93 else
94 {
95 foreach (bool l1 in YP.unify(this, arg))
96 yield return false;
97 }
98 }
99
100 public override string ToString()
101 {
102 object value = getValue();
103 if (value == this)
104 return "Variable";
105 else
106 return getValue().ToString();
107 }
108
109 /// <summary>
110 /// If bound, call YP.addUniqueVariables on the value. Otherwise, if this unbound
111 /// variable is not already in variableSet, add it.
112 /// </summary>
113 /// <param name="variableSet"></param>
114 public void addUniqueVariables(List<Variable> variableSet)
115 {
116 if (_isBound)
117 YP.addUniqueVariables(getValue(), variableSet);
118 else
119 {
120 if (variableSet.IndexOf(this) < 0)
121 variableSet.Add(this);
122 }
123 }
124
125 /// <summary>
126 /// If bound, return YP.makeCopy for the value, else return copyStore.getCopy(this).
127 /// However, if copyStore is null, just return this.
128 /// </summary>
129 /// <param name="copyStore"></param>
130 /// <returns></returns>
131 public object makeCopy(Variable.CopyStore copyStore)
132 {
133 if (_isBound)
134 return YP.makeCopy(getValue(), copyStore);
135 else
136 return copyStore == null ? this : copyStore.getCopy(this);
137 }
138
139 public bool termEqual(object term)
140 {
141 if (_isBound)
142 return YP.termEqual(getValue(), term);
143 else
144 return this == YP.getValue(term);
145 }
146
147 public bool ground()
148 {
149 if (_isBound)
150 // This is usually called by YP.ground which already did getValue, so this
151 // should never be reached, but check anyway.
152 return YP.ground(getValue());
153 else
154 return false;
155 }
156
157 /// <summary>
158 /// A CopyStore is used by makeCopy to track which Variable objects have
159 /// been copied.
160 /// </summary>
161 public class CopyStore
162 {
163 private List<Variable> _inVariableSet = new List<Variable>();
164 private List<Variable> _outVariableSet = new List<Variable>();
165
166 /// <summary>
167 /// If inVariable has already been copied, return its copy. Otherwise,
168 /// return a fresh Variable associated with inVariable.
169 /// </summary>
170 /// <param name="inVariable"></param>
171 /// <returns></returns>
172 public Variable getCopy(Variable inVariable)
173 {
174 int index = _inVariableSet.IndexOf(inVariable);
175 if (index >= 0)
176 return _outVariableSet[index];
177 else
178 {
179 Variable outVariable = new Variable();
180 _inVariableSet.Add(inVariable);
181 _outVariableSet.Add(outVariable);
182 return outVariable;
183 }
184 }
185
186 /// <summary>
187 /// Return the number of unique variables that have been copied.
188 /// </summary>
189 /// <returns></returns>
190 public int getNUniqueVariables()
191 {
192 return _inVariableSet.Count;
193 }
194 }
195 }
196}