private HashSet <IToken> First(IToken token)
{
if (token.IsTerminal)
{
return new HashSet <IToken>()
{
token
}
}
;
NonTerminal nonterm = token as NonTerminal;
if (LeftRecursiveNonterminals.Contains(nonterm))
{
throw new InvalidOperationException("Nonterminal can't be left recursive!");
}
HashSet <IToken> firstSet = new HashSet <IToken>();
HashSet <IToken> eps = new HashSet <IToken>()
{
__Epsilon
};
bool containsEps = true;
foreach (var rule in nonterm.Rules)
{
containsEps = true;
foreach (var t in rule.RightPart)
{
if (containsEps)
{
var first_yi = First(t);
containsEps = first_yi.Contains(__Epsilon);
first_yi.ExceptWith(eps);
firstSet.UnionWith(first_yi);
}
else
{
break;
}
}
}
if (containsEps || EpsilonNonterminals.Contains(nonterm))
{
firstSet.Add(__Epsilon);
}
return(firstSet);
}
private bool IsEpsilonProductive(IToken token)
{
return(token.IsTerminal ? token == __Epsilon : (EpsilonNonterminals.Contains(token)));
}
