/// <summary>
/// Applies backwards the relevant operator effects and operator preconditions to the given target conditions.
/// </summary>
/// <param name="expression">Target conditions in CNF.</param>
/// <param name="expressionSubstitution">Variables substitution of the expression.</param>
/// <returns>Preceding conditions.</returns>
private ConditionsCNF ApplyBackwardsImpl(ConditionsCNF expression, ISubstitution expressionSubstitution)
{
UsedGroundedPredicates.Clear();
UsedGroundedFunctions.Clear();
ExpressionSubstitution = expressionSubstitution;
// remove positively contributing effects from the target conditions
ConditionsCNF resultExpression = ProcessPrimitiveEffects(expression);
resultExpression = ProcessForallEffects(resultExpression);
resultExpression = ProcessWhenEffects(resultExpression);
// unite processed conditions with partially grounded preconditions of the operator
if (OperatorPreconditions != null)
{
var preconditions = ClearRigidRelations(OperatorPreconditions);
resultExpression.Merge((ConditionsCNF)GroundConditions(preconditions).GetCNF());
}
return(resultExpression);
}
/// <summary>
/// Visits the expression.
/// </summary>
/// <param name="expression">Expression.</param>
public IElementCNF Visit(EqualsLiteralCNF expression)
{
var objectAssignEffects = Effects.GroundedObjectFunctionAssignmentEffects;
if (objectAssignEffects.Count == 0)
{
return(expression.Clone());
}
Func <ITerm, ITerm> transformArgument = null;
transformArgument = (term) =>
{
ObjectFunctionTerm objectFunction = term as ObjectFunctionTerm;
if (objectFunction != null)
{
ITerm assignmentValue;
if (objectAssignEffects.TryGetValue(GroundAtom(objectFunction.FunctionAtom), out assignmentValue))
{
UsedGroundedFunctions.Add(objectFunction.FunctionAtom);
return(transformArgument(assignmentValue));
}
}
return(term.Clone());
};
ITerm transformedLeftTerm = transformArgument(expression.LeftArgument);
ITerm transformedRightTerm = transformArgument(expression.RightArgument);
bool termsEqual = transformedLeftTerm.Equals(transformedRightTerm);
if ((termsEqual && !expression.IsNegated) || (!termsEqual && expression.IsNegated))
{
// exact constant assignment (or unassignment with negated equals) -> positively contributing, i.e. remove
return(null);
}
return(new EqualsLiteralCNF(transformedLeftTerm, transformedRightTerm, expression.IsNegated));
}
/// <summary>
/// Visits the expression.
/// </summary>
/// <param name="expression">Expression.</param>
public IElementCNF Visit(NumericCompareLiteralCNF expression)
{
// 1.) Evaluates both of the arguments by NumericAssignmentsBackwardsReplacer - every numeric function instance is replaced by
// the available numeric assignments from effects and the whole numeric expression is reduced (partially or fully evaluated).
// 2.) In case of the full reduction of both arguments, the numeric comparison is evaluated - if successfully, the whole condition
// is satisfied and we can remove it (i.e. return null).
// 3.) Otherwise, the modified numeric compare expression is returned, replacing the original condition.
var numericAssignEffects = Effects.GroundedNumericFunctionAssignmentEffects;
if (numericAssignEffects.Count == 0)
{
// no assignment effects available, just return a copy of the original expression
return(expression.Clone());
}
NumericAssignmentsBackwardsReplacer replacer = new NumericAssignmentsBackwardsReplacer(numericAssignEffects, GroundingManager, OperatorSubstitution, ExpressionSubstitution);
INumericExpression newLeftNumericExpression = replacer.Replace(expression.LeftArgument);
INumericExpression newRightNumericExpression = replacer.Replace(expression.RightArgument);
UsedGroundedFunctions.UnionWith(replacer.ReplacedFunctionAtomsInSubExpression);
Number leftNumber = newLeftNumericExpression as Number;
Number rightNumber = newRightNumericExpression as Number;
if (leftNumber != null && rightNumber != null)
{
bool relationHolds = NumericCompareExpression.ApplyCompare(expression.Operator, leftNumber.Value, rightNumber.Value);
if ((relationHolds && !expression.IsNegated) || (!relationHolds && expression.IsNegated))
{
// the numeric comparison was successful -> condition is satisfied, i.e. remove
return(null);
}
}
// modified numeric compare expression, replacing the original one
return(new NumericCompareLiteralCNF(expression.Operator, newLeftNumericExpression, newRightNumericExpression, expression.IsNegated));
}
