C++ Grammar::GetSymbol方法代码示例

//controi todos os first(A) first(a) da gramatica g
FirstSets BuildFirstSets3(const Grammar& g)
{
    FirstSets  first;

    //if X is a terminal: FIRST (X) = X
    //X is epsilon: FIRST (X) = epsilon
    for (int k = 0 ; k < g.GetNumOfGrammarSymbols(); k++)
    {
        if (g.GetSymbol(k)->IsTerminal())
        {
            std::set<const GrammarSymbol*> fs;
            fs.insert(g.GetSymbol(k));
            first.AddSet(g.GetSymbol(k), std::move(fs));
        }
    }

    bool added = true;

    while (added)
    {
        added = false;

        for (int i = 0 ; i < g.GetNumOfProductions(); i++)
        {
            const Production& production  = g.GetProduction(i);
            const GrammarSymbol* X = production.GetLeftSymbol();
            int epsilonCount = 0;

            for (int k = 0 ; k < production.GetNumOfRightSymbols(); k++)
            {
                // Put FIRST (Y1) - {epsilon} into FIRST (X)
                if (k == 0)
                {
                    //Copia todos (-epsilon) de Y1first para Y1first(X)
                    auto Y1first = first.CreateGet(production.GetRightSymbol(k));

                    if (Y1first.find(g.epsilon()) != Y1first.end())
                    {
                        epsilonCount = 1;
                    }

                    for (auto it = Y1first.begin(); it != Y1first.end(); it++)
                    {
                        if (*it != g.epsilon())
                        {
                            const GrammarSymbol* ptemp = *it;
                            added = added || first.AddToSet(X, ptemp);
                        }
                    }

                    continue;
                }

                // O anterior tinha epsilon?
                auto YKfirst = first.CreateGet(production.GetRightSymbol(k - 1));

                if (YKfirst.find(g.epsilon()) != YKfirst.end())
                {
                    epsilonCount++;
                    //Copia todos (-epsilon) para first(X)
                    auto Y1first = first.CreateGet(production.GetRightSymbol(k));

                    for (auto it = Y1first.begin(); it != Y1first.end(); it++)
                    {
                        if (*it != g.epsilon())
                        {
                            const GrammarSymbol* ptemp = *it;
                            added = added || first.AddToSet(X,  ptemp);
                        }
                    }
                }
                else
                {
                    //se o anterior nao tinha epsilon ja pode parar
                    break;
                }
            }

            // se todos eram epsilon entao adicionar epsilon TODO -1
            if (epsilonCount != 0 &&
                    epsilonCount == production.GetNumOfRightSymbols())
            {
                added = added || first.AddToSet(X,  g.epsilon());
            }
        }
    }

    return first;
}

//controi todos os follow(A) da gramatica g
FollowSets BuildFolowSets3(Grammar& g,  const FirstSets& first)
{
    FollowSets follow;
    //Follow(start-symbol):= {$};
    follow.AddToSet(g.GetStartSymbol(), g.endmarker());

    //for all nonterminals A != start-symbol do Follow(A):={};
    for (int i = 0 ; i < g.GetNumOfGrammarSymbols(); i++)
    {
        const GrammarSymbol* pgs = g.GetSymbol(i);

        if (!pgs->IsTerminal() && pgs != g.GetStartSymbol())
        {
            follow.CreateGet(pgs);
        }
    }

    bool changed = true;

    while (changed)
    {
        changed = false;

        // Para cada producao A -> X1...Xn
        for (int k = 0 ; k < g.GetNumOfProductions(); k++)
        {
            const Production& A = g.GetProduction(k);
            Print(std::wcout, A);
            std::wcout << std::endl;

            for (int i = 0 ; i < A.GetNumOfRightSymbols(); i++)
            {
                //If there is a production A -> alfa B beta , then everything in FIRST(beta) except epsilon
                //is in FOLLOW(B).
                const GrammarSymbol* Xi = A.GetRightSymbol(i);

                //Para cada nao terminal Xi da producao
                if (!Xi->IsTerminal())
                {
                    //add First(Xi+1..Xn) - {epsilon} to Follow(Xi)
                    std::set<const GrammarSymbol*> firstXi1_Xn;
                    bool epsilon_is_in_firstXi1_Xn = false;

                    //se Xi não é o ultimo
                    if (i < (A.GetNumOfRightSymbols() - 1))
                    {
                        firstXi1_Xn = GetFirstSet(first, g, A, i + 1);

                        for (auto it = firstXi1_Xn.begin(); it != firstXi1_Xn.end(); ++it)
                        {
                            if (*it != g.epsilon())
                            {
                                if (follow.AddToSet(Xi, *it))
                                {
                                    changed = true;
                                }
                            }
                            else
                            {
                                epsilon_is_in_firstXi1_Xn = true;
                            }
                        }
                    }

                    // If there is a production A -> alfaB, or a production A -> alfa B beta , where
                    // FIRST(beta) contains epsilon, then everything in FOLLOW (A) is in FOLLOW (B) .
                    if (i == (A.GetNumOfRightSymbols() - 1) ||
                            epsilon_is_in_firstXi1_Xn)
                    {
                        //add Follow(A) to Follow(Xi)
                        auto FollowA = follow.Get(A.GetLeftSymbol());

                        for (auto it = FollowA.begin(); it != FollowA.end(); ++it)
                        {
                            if (follow.AddToSet(Xi, *it))
                            {
                                changed = true;
                            }
                        }
                    }
                }//para este Xi
            } //para cada Xi
        } //para cada producao
    } //enquando mudar...

    return follow;
}