private static IStringEvaluator combineTokens(List <IToken> tokens)
{
var valStack = new Stack <IStringEvaluator>();
var opeStack = new Stack <OperatorEvaluator>();
bool valueLasted = false;
Action <OperatorEvaluator> fnResolveOperator = (OperatorEvaluator ope) => {
ope.Right = valStack.Pop();
ope.Left = valStack.Pop();
valStack.Push(ope);
};
foreach (var token in tokens)
{
IStringEvaluator evaluator = token.getEvaluator();
if (evaluator is ValueEvaluator)
{
if (valueLasted)
{
throw new FormatException("Value expression duplicated.");
}
valStack.Push(evaluator);
valueLasted = true;
}
else if (evaluator is OperatorEvaluator)
{
OperatorEvaluator ope = (OperatorEvaluator)evaluator;
if (!valueLasted)
{
throw new FormatException("Operator expression duplicated.");
}
if (opeStack.Count > 0)
{
if (opeStack.Last().getPriority() <= ope.getPriority())
{
fnResolveOperator(opeStack.Pop());
}
}
opeStack.Push(ope);
valueLasted = false;
}
}
while (opeStack.Count > 0)
{
fnResolveOperator(opeStack.Pop());
}
if (valStack.Count == 0)
{
throw new FormatException("Operator expression is none.");
}
return(valStack.Last());
}
