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/*
* Copyright (C) 2007-2008, Jeff Thompson
*
* 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 copyright holder 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.
*/
using System;
using System.Collections;
using System.Collections.Generic;
namespace OpenSim.Region.ScriptEngine.Shared.YieldProlog
{
public interface IUnifiable
{
IEnumerable<bool> unify(object arg);
void addUniqueVariables(List<Variable> variableSet);
object makeCopy(Variable.CopyStore copyStore);
bool termEqual(object term);
bool ground();
}
/// <summary>
/// A Variable is passed to a function so that it can be unified with
/// value or another Variable. See getValue and unify for details.
/// </summary>
public class Variable : IUnifiable
{
// Use _isBound separate from _value so that it can be bound to any value,
// including null.
private bool _isBound = false;
private object _value;
/// <summary>
/// If this Variable is unbound, then just return this Variable.
/// Otherwise, if this has been bound to a value with unify, return the value.
/// If the bound value is another Variable, this follows the "variable chain"
/// to the end and returns the final value, or the final Variable if it is unbound.
/// For more details, see http://yieldprolog.sourceforge.net/tutorial1.html
/// </summary>
/// <returns></returns>
public object getValue()
{
if (!_isBound)
return this;
object result = _value;
while (result is Variable)
{
if (!((Variable)result)._isBound)
return result;
// Keep following the Variable chain.
result = ((Variable)result)._value;
}
return result;
}
/// <summary>
/// If this Variable is bound, then just call YP.unify to unify this with arg.
/// (Note that if arg is an unbound Variable, then YP.unify will bind it to
/// this Variable's value.)
/// Otherwise, bind this Variable to YP.getValue(arg) and yield once. After the
/// yield, return this Variable to the unbound state.
/// For more details, see http://yieldprolog.sourceforge.net/tutorial1.html
/// </summary>
/// <param name="arg"></param>
/// <returns></returns>
public IEnumerable<bool> unify(object arg)
{
if (!_isBound)
{
_value = YP.getValue(arg);
if (_value == this)
// We are unifying this unbound variable with itself, so leave it unbound.
yield return false;
else
{
_isBound = true;
try
{
yield return false;
}
finally
{
// Remove the binding.
_isBound = false;
}
}
}
else
{
// disable warning on l1, don't see how we can
// code this differently
#pragma warning disable 0168
foreach (bool l1 in YP.unify(this, arg))
yield return false;
#pragma warning restore 0168
}
}
public override string ToString()
{
object value = getValue();
if (value == this)
return "_Variable";
else
return getValue().ToString();
}
/// <summary>
/// If bound, call YP.addUniqueVariables on the value. Otherwise, if this unbound
/// variable is not already in variableSet, add it.
/// </summary>
/// <param name="variableSet"></param>
public void addUniqueVariables(List<Variable> variableSet)
{
if (_isBound)
YP.addUniqueVariables(getValue(), variableSet);
else
{
if (variableSet.IndexOf(this) < 0)
variableSet.Add(this);
}
}
/// <summary>
/// If bound, return YP.makeCopy for the value, else return copyStore.getCopy(this).
/// However, if copyStore is null, just return this.
/// </summary>
/// <param name="copyStore"></param>
/// <returns></returns>
public object makeCopy(Variable.CopyStore copyStore)
{
if (_isBound)
return YP.makeCopy(getValue(), copyStore);
else
return copyStore == null ? this : copyStore.getCopy(this);
}
public bool termEqual(object term)
{
if (_isBound)
return YP.termEqual(getValue(), term);
else
return this == YP.getValue(term);
}
public bool ground()
{
if (_isBound)
// This is usually called by YP.ground which already did getValue, so this
// should never be reached, but check anyway.
return YP.ground(getValue());
else
return false;
}
/// <summary>
/// A CopyStore is used by makeCopy to track which Variable objects have
/// been copied.
/// </summary>
public class CopyStore
{
private List<Variable> _inVariableSet = new List<Variable>();
private List<Variable> _outVariableSet = new List<Variable>();
/// <summary>
/// If inVariable has already been copied, return its copy. Otherwise,
/// return a fresh Variable associated with inVariable.
/// </summary>
/// <param name="inVariable"></param>
/// <returns></returns>
public Variable getCopy(Variable inVariable)
{
int index = _inVariableSet.IndexOf(inVariable);
if (index >= 0)
return _outVariableSet[index];
else
{
Variable outVariable = new Variable();
_inVariableSet.Add(inVariable);
_outVariableSet.Add(outVariable);
return outVariable;
}
}
/// <summary>
/// Return the number of unique variables that have been copied.
/// </summary>
/// <returns></returns>
public int getNUniqueVariables()
{
return _inVariableSet.Count;
}
}
}
}
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