public override void VisitMultiplicationOperationElement(MultiplicationOperationElement element)
{
VisitElement(element.getLhs());
VisitElement(element.getRhs());
int rhs = mStack.Pop();
int lhs = mStack.Pop();
int result = rhs * lhs;
mStack.Push(result);
}
public override void VisitPrintOperationElement(PrintOperationElement element){