public SyntaxTreeNode this[Nonterminal nonterminal]
{
get
{
return(_children.FirstOrDefault(child => child.Value.Equals(nonterminal)));
}
}
private static SymbolsChain FirstRightSideChain(SymbolsChain chain, Nonterminal nonterminal)
{
int index = chain.FindIndex(nonterminal);
if (index == -1)
{
return(null);
}
return(chain.Subchain(index + 1));
}
public static ISet <Terminal> Follow(IEnumerable <Production> productions, Nonterminal nonterminal, Nonterminal axiom)
{
var follow = CreateNewEmptyTerminalSet();
if (nonterminal.Equals(axiom))
{
follow.Add(GeneralizedTerminal.EndOfText);
}
// X -> ... A ..., A - specified symbol
var appropriateProductions = productions.Where(p => p.RightPart.Contains(nonterminal));
foreach (var production in appropriateProductions)
{
// X -> ... A
if (production.RightPart.Last.Equals(nonterminal))
{
// preventing infinite follow call
if (!production.LeftPart.Equals(nonterminal))
{
follow.UnionWith(Follow(productions, production.LeftPart, axiom));
}
}
foreach (var rightSideChain in RightSideChains(production.RightPart, nonterminal))
//var rightSideChain = FirstRightSideChain(production.RightPart, nonterminal);
{
// X -> ... A g
//if (!production.RightPart.Last.Equals(nonterminal))
//{
follow.UnionWith(First(productions, rightSideChain).ExceptTerminal(GeneralizedTerminal.Epsilon));
//}
// X -> ... A h, where h is epsilon generating chain
if (First(productions, rightSideChain).Contains(GeneralizedTerminal.Epsilon))
{
// preventing infinite follow call
if (!production.LeftPart.Equals(nonterminal))
{
follow.UnionWith(Follow(productions, production.LeftPart, axiom));
}
}
}
}
return(follow);
}
public Production(Nonterminal leftPart, SymbolsChain rightPart)
{
LeftPart = leftPart;
RightPart = rightPart;
}
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);
}
