public static ISet <Terminal> First(IEnumerable <Production> productions, SymbolsChain chain)
{
var first = CreateNewEmptyTerminalSet();
bool allSymbolsIsEpsilonGenerating = true;
var enumerator = chain.GetEnumerator();
ISet <Terminal> curFirst = null;
while (enumerator.MoveNext())
{
curFirst = First(productions, enumerator.Current);
first.UnionWith(curFirst.ExceptTerminal(GeneralizedTerminal.Epsilon));
if (!curFirst.Contains(GeneralizedTerminal.Epsilon))
{
allSymbolsIsEpsilonGenerating = false;
break;
}
}
if (allSymbolsIsEpsilonGenerating)
{
first.Add(GeneralizedTerminal.Epsilon);
}
return(first);
}
private static SymbolsChain FirstRightSideChain(SymbolsChain chain, Nonterminal nonterminal)
{
int index = chain.FindIndex(nonterminal);
if (index == -1)
{
return(null);
}
return(chain.Subchain(index + 1));
}
private static IEnumerable <SymbolsChain> RightSideChains(SymbolsChain chain, Nonterminal nonterminal)
{
var rightChains = new List <SymbolsChain>();
SymbolsChain current = chain;
do
{
current = FirstRightSideChain(current, nonterminal);
if (current != null)
{
rightChains.Add(current);
}
else
{
break;
}
} while (true);
return(rightChains);
}
public Production(Nonterminal leftPart, SymbolsChain rightPart)
{
LeftPart = leftPart;
RightPart = rightPart;
}