private void GetIdentifiers(HashSet <string> set)
{
switch (kind)
{
case Kind.RegexpUnion:
case Kind.RegexpConcatenation:
case Kind.RegexpIntersection:
exp1.GetIdentifiers(set);
exp2.GetIdentifiers(set);
break;
case Kind.RegexpOptional:
case Kind.RegexpRepeat:
case Kind.RegexpRepeatMin:
case Kind.RegexpRepeatMinMax:
case Kind.RegexpComplement:
exp1.GetIdentifiers(set);
break;
case Kind.RegexpAutomaton:
set.Add(s);
break;
}
}