public Symbols GetTerminals()
{
Symbols symbols = new Symbols();
foreach (Symbol s in Symbols)
{
if (s is TerminalSymbol)
{
symbols.Add(s);
}
}
return(symbols);
}
public void DetermineProductionSymbols(Symbols symbols)
{
if (Type == RuleType.Terminal || Type == RuleType.NonTerminal)
{
symbols.Add(Symbol);
}
else
{
foreach (Rule rule in Rules)
{
rule.DetermineProductionSymbols(symbols);
}
}
}
internal bool DetermineFirstTerminals(Symbols FirstTerminals, int index)
{
// indicates if Nonterminal can evaluate to an empty terminal (e.g. in case T -> a? or T -> a*)
// in which case the parent rule should continue scanning after this nonterminal for Firsts.
bool containsEmpty = false; // assume terminal is found
switch (Type)
{
case RuleType.Terminal:
if (Symbol == null)
{
return(true);
}
if (!FirstTerminals.Exists(Symbol))
{
FirstTerminals.Add(Symbol);
}
else
{
Console.WriteLine("throw new Exception(\"Terminal already exists\");");
}
break;
case RuleType.NonTerminal:
if (Symbol == null)
{
return(true);
}
NonTerminalSymbol nts = Symbol as NonTerminalSymbol;
containsEmpty = nts.DetermineFirstTerminals();
// add first symbols of the nonterminal if not already added
foreach (TerminalSymbol t in nts.FirstTerminals)
{
if (!FirstTerminals.Exists(t))
{
FirstTerminals.Add(t);
}
else
{
Console.WriteLine("throw new Exception(\"Terminal already exists\");");
}
}
break;
case RuleType.Choice:
{
// all subrules must be evaluated to determine if they contain first terminals
// if any subrule contains an empty, then this rule also contains an empty
foreach (Rule r in Rules)
{
containsEmpty |= r.DetermineFirstTerminals(FirstTerminals);
}
break;
}
case RuleType.OneOrMore:
{
// if a non-empty subrule was found, then stop further parsing.
foreach (Rule r in Rules)
{
containsEmpty = r.DetermineFirstTerminals(FirstTerminals);
if (!containsEmpty) // found the final set of first terminals
{
break;
}
}
break;
}
case RuleType.Concat:
{
// if a non-empty subrule was found, then stop further parsing.
// start scanning from Index
for (int i = index; i < Rules.Count; i++)
{
containsEmpty = Rules[i].DetermineFirstTerminals(FirstTerminals);
if (!containsEmpty) // found the final set of first terminals
{
break;
}
}
// assign this concat rule to each terminal
foreach (TerminalSymbol t in FirstTerminals)
{
t.Rule = this;
}
break;
}
case RuleType.Option:
case RuleType.ZeroOrMore:
{
// empty due to the nature of this rule (A? or A* can always be empty)
containsEmpty = true;
// if a non-empty subrule was found, then stop further parsing.
foreach (Rule r in Rules)
{
containsEmpty |= r.DetermineFirstTerminals(FirstTerminals);
if (!containsEmpty) // found the final set of first terminals
{
break;
}
}
break;
}
default:
throw new NotImplementedException();
}
return(containsEmpty);
}