/// <summary>
/// Retrieve real expression of varexpression
/// </summary>
/// <param name="expression">VarExpression to get real expression from</param>
/// <returns>Real expression value</returns>
private Expression GetReferenceExpression(VarExpression expression)
{
String identifier = expression.GetVariableIdentifier();
Expression referenceExpr = null;
do
{
if (SymbolTable.ContainsVariable(identifier))
{
referenceExpr = SymbolTable.GetVariableDefinition(identifier);
if (referenceExpr == expression && SymbolTable.GetParentSymbolTable() != null)
{ //Get reference from parent symboltable
referenceExpr = SymbolTable.GetParentSymbolTable().GetVariableDefinition(identifier);
}
}
} while (referenceExpr is VarExpression);
return(referenceExpr);
}
/// <summary>
/// Interpret VarExpression
/// </summary>
/// <param name="expression">VarExpression to interpret</param>
public override void Visit(VarExpression expression)
{
//Check if variable does exist
String varName = expression.GetVariableIdentifier();
Expression check = SymbolTable.GetVariableDefinition(varName);
//If reference has been made to parent variable with same name, take parent reference
if (check == expression && SymbolTable.GetParentSymbolTable() != null)
{
check = SymbolTable.GetParentSymbolTable().GetVariableDefinition(varName);
}
if (check != null)
{ //Visit variable to retrieve current value
check.AcceptVisitor(this);
}
else
{
TextValue = "undef";
}
}
/// <summary>
/// Method which evaluates an predicate and returns true or false
/// </summary>
/// <param name="predicate">Predicate to evaluate</param>
/// <returns>True if predicate is true, otherwise false</returns>
private bool EvaluatePredicate(Predicate predicate)
{
if (predicate is IsPredicate)
{ //Evaluate Expression Predicate
IsPredicate isPredicate = (IsPredicate)predicate;
Expression expression = isPredicate.GetExpression();
//In case of VarExpression, get expression from symboltable
if (expression is VarExpression)
{
expression = GetReferenceExpression((VarExpression)expression);
if (expression == null)
{
return(false);
}
}
//If right type return true, otherwise false
if (isPredicate.GetType() is StringType)
{
return(expression is TextExpression);
}
else if (isPredicate.GetType() is ListType)
{
return(expression is ListExpression);
}
else if (isPredicate.GetType() is RecordType)
{
return(expression is RecordExpression);
}
else
{ //No match between types which could be checked, so false
return(false);
}
}
else if (predicate is ExpressionPredicate)
{ //Evaluate Expression Predicate
ExpressionPredicate expressionPredicate = (ExpressionPredicate)predicate;
Expression expression = expressionPredicate.GetExpression();
if (expression is FieldExpression)
{ //Check if specific field exists in record (not null)
Expression expr = GetExpression((FieldExpression)expression);
return(expr != null);
}
else if (expression is VarExpression)
{ //Check if specific variable is defined
VarExpression varExpr = (VarExpression)expression;
return(SymbolTable.ContainsVariable(varExpr.GetVariableIdentifier()));
}
else
{ //Other expressions are always true, because they doesn't refer to something
return(true);
}
}
else if (predicate is AndPredicate)
{ //Evaluate And Predicate
AndPredicate andPredicate = (AndPredicate)predicate;
return(EvaluatePredicate(andPredicate.GetLeftPredicate()) && EvaluatePredicate(andPredicate.GetLeftPredicate()));
}
else if (predicate is OrPredicate)
{ //Evaluate Or Predicate
OrPredicate orPredicate = (OrPredicate)predicate;
return(EvaluatePredicate(orPredicate.GetLeftPredicate()) || EvaluatePredicate(orPredicate.GetRightPredicate()));
}
else if (predicate is NotPredicate)
{ //Evaluate Not Predicate
NotPredicate notPredicate = (NotPredicate)predicate;
return(!EvaluatePredicate(notPredicate.GetPredicate()));
}
return(false);
}
