unary and binary operations

Ferenc Szontágh

2025-04-17 ba9a9199d01b0fdd4bf9a54914f8058bf71f30c5

 src/Parser/Parser.hpp

@@ -3,17 +3,19 @@

#include <algorithm>
#include <memory>
#include <sstream>  // Hibaüzenetekhez
#include <stack>
#include <stdexcept>
#include <string>
#include <vector>

// Szükséges header-ök a Lexer és Symbol komponensekből
#include "Interpreter/ExpressionBuilder.hpp"
#include "Interpreter/OperationsFactory.hpp"
#include "Lexer/Token.hpp"
#include "Lexer/TokenType.hpp"  // Enum és TypeToString
#include "Lexer/TokenType.hpp"
#include "Parser/ParsedExpression.hpp"
#include "Symbols/ParameterContainer.hpp"
#include "Symbols/SymbolContainer.hpp"
#include "Symbols/SymbolFactory.hpp"
#include "Symbols/Value.hpp"  // Symbols::Value miatt
#include "Symbols/Value.hpp"

namespace Parser {

@@ -32,11 +34,13 @@
  public:
    Parser() {}

    void parseProgram(const std::vector<Lexer::Tokens::Token> & tokens, std::string_view input_string) {
    void parseScript(const std::vector<Lexer::Tokens::Token> & tokens, std::string_view input_string,
                     const std::string & filename) {
        tokens_              = tokens;
        input_str_view_      = input_string;
        current_token_index_ = 0;
        symbol_container_    = std::make_unique<Symbols::SymbolContainer>();
        current_filename_    = filename;

        try {
            while (!isAtEnd() && currentToken().type != Lexer::Tokens::Type::END_OF_FILE) {
                parseStatement();
@@ -52,21 +56,14 @@
        }
    }

    const std::shared_ptr<Symbols::SymbolContainer> & getSymbolContainer() const {
        if (!symbol_container_) {
            throw std::runtime_error("Symbol container is not initialized.");
        }
        return symbol_container_;
    }

    static const std::unordered_map<std::string, Lexer::Tokens::Type>              keywords;
    static const std::unordered_map<Lexer::Tokens::Type, Symbols::Variables::Type> variable_types;

  private:
    std::vector<Lexer::Tokens::Token>         tokens_;
    std::string_view                          input_str_view_;
    size_t                                    current_token_index_;
    std::shared_ptr<Symbols::SymbolContainer> symbol_container_;
    std::vector<Lexer::Tokens::Token> tokens_;
    std::string_view                  input_str_view_;
    size_t                            current_token_index_;
    std::string                       current_filename_;

    // Token Stream Kezelő és Hibakezelő segédfüggvények (változatlanok)
    const Lexer::Tokens::Token & currentToken() const {
@@ -182,7 +179,7 @@
    void parseStatement() {
        const auto & token_type = currentToken().type;

        if (token_type == Lexer::Tokens::Type::KEYWORD_FUNCTION) {
        if (token_type == Lexer::Tokens::Type::KEYWORD_FUNCTION_DECLARATION) {
            parseFunctionDefinition();
            return;
        }
@@ -197,40 +194,33 @@
        reportError("Unexpected token at beginning of statement");
    }

    // parseVariableDefinition (SymbolFactory használata már korrekt volt)
    void parseVariableDefinition() {
        Symbols::Variables::Type var_type_enum = parseType();
        // A típus stringjének tárolása csak a debug kiíráshoz kell
        //std::string              var_type_str  = tokens_[current_token_index_ - 1].value;
        std::cout << "var_name: " << currentToken().lexeme << std::endl;
        Symbols::Variables::Type var_type = parseType();

        Lexer::Tokens::Token id_token = expect(Lexer::Tokens::Type::VARIABLE_IDENTIFIER);
        std::string          var_name = id_token.value;
        // Levágjuk a '$' jelet, ha a lexer mégis benne hagyta

        if (!var_name.empty() && var_name[0] == '$') {
            var_name = var_name.substr(1);
        }
        const auto ns = Symbols::SymbolContainer::instance()->currentScopeName();

        expect(Lexer::Tokens::Type::OPERATOR_ASSIGNMENT, "=");
        Symbols::Value initial_value = parseValue(var_type_enum);
        /*
        Symbols::Value initial_value = parseValue(var_type);

        Interpreter::OperationsFactory::defineSimpleVariable(var_name, initial_value, ns, this->current_filename_,
                                                             id_token.line_number, id_token.column_number);
*/

        auto expr = parseParsedExpression(var_type);
        Interpreter::OperationsFactory::defineVariableWithExpression(
            var_name, var_type, std::move(expr), ns, current_filename_, id_token.line_number, id_token.column_number);
        expect(Lexer::Tokens::Type::PUNCTUATION, ";");

        std::string context  = "global";  // Globális változó
        // SymbolFactory használata a létrehozáshoz
        auto variable_symbol = Symbols::SymbolFactory::createVariable(var_name, initial_value, context, var_type_enum);

        // Ellenőrzés és definíció az *aktuális* scope-ban (ami itt a globális)
        if (symbol_container_->exists("variables", var_name)) {
            reportError("Variable '" + var_name + "' already defined in this scope");
        }
        symbol_container_->define("variables", variable_symbol);

        // Debugging kiírás (változatlan)
        // std::cout << "Parsed variable: " << var_type_str << " " << id_token.value << " = ... ;\n";
    }

    // *** MÓDOSÍTOTT parseFunctionDefinition ***
    void parseFunctionDefinition() {
        expect(Lexer::Tokens::Type::KEYWORD_FUNCTION);
        expect(Lexer::Tokens::Type::KEYWORD_FUNCTION_DECLARATION);
        Lexer::Tokens::Token     id_token         = expect(Lexer::Tokens::Type::IDENTIFIER);
        std::string              func_name        = id_token.value;
        Symbols::Variables::Type func_return_type = Symbols::Variables::Type::NULL_TYPE;
@@ -242,7 +232,6 @@
        if (currentToken().type != Lexer::Tokens::Type::PUNCTUATION || currentToken().value != ")") {
            while (true) {
                // Paraméter típusa
                //size_t                   type_token_index = current_token_index_;  // Elmentjük a típus token indexét
                Symbols::Variables::Type param_type = parseType();  // Ez elfogyasztja a type tokent

                // Paraméter név ($variable)
@@ -275,50 +264,10 @@
            }
        }

        auto function_symbol =
            Symbols::SymbolFactory::createFunction(func_name, "global", param_infos, "", func_return_type);
        if (symbol_container_->exists("functions", func_name)) {
            reportError("Function '" + func_name + "' already defined in this scope");
        }

        Lexer::Tokens::Token opening_brace = expect(Lexer::Tokens::Type::PUNCTUATION, "{");

        symbol_container_->define("functions", function_symbol);

        // only parse the body if we checked out if not exists the function and created the symbol
        Symbols::SymbolContainer func_symbols =
            parseFunctionBody(opening_brace, func_return_type != Symbols::Variables::Type::NULL_TYPE);

        // create new container for the function

        std::cout << "Defined function symbol: " << func_name << " in global scope.\n";

        // 3. Új scope nyitása a függvény paraméterei (és később lokális változói) számára
        symbol_container_->enterScope();
        //std::cout << "Entered scope for function: " << func_name << "\n";

        // 4. Paraméterek definiálása mint változók az *új* (függvény) scope-ban
        const std::string & param_context = func_name;  // Paraméter kontextusa a függvény neve
        for (const auto & p_info : param_infos) {
            auto param_symbol = Symbols::SymbolFactory::createVariable(p_info.name,       // Név '$' nélkül
                                                                       Symbols::Value(),  // Alapértelmezett/üres érték
                                                                       param_context,     // Kontextus
                                                                       p_info.type        // Típus
            );

            if (symbol_container_->exists("variables", p_info.name)) {
                reportError("Parameter name '" + p_info.name + "' conflicts with another symbol in function '" +
                            func_name + "'");
            }
            symbol_container_->define("variables", param_symbol);
        }

        // 5. Függvény scope elhagyása
        symbol_container_->leaveScope();
        //std::cout << "Left scope for function: " << func_name << "\n";

        // Debugging kiírás (változatlan)
        // std::cout << "Parsed function: " << func_name << " (...) { ... } scope handled.\n";
        parseFunctionBody(opening_brace, func_name, func_return_type, param_infos);
    }

    // --- Elemzési Segédfüggvények ---
@@ -337,118 +286,96 @@
        reportError("Expected type keyword (string, int, double, float)");
    }

    // value : STRING_LITERAL | NUMBER
    // Feldolgozza az értéket a várt típus alapján.
    Symbols::Value parseValue(Symbols::Variables::Type expected_var_type) {
        Lexer::Tokens::Token token = currentToken();
        Lexer::Tokens::Token token       = currentToken();
        bool                 is_negative = false;

        /// find if this is a function call
        if (token.type == Lexer::Tokens::Type::IDENTIFIER && peekToken().lexeme == "(") {
            for (const auto & symbol_ptr : this->symbol_container_->listNamespace("functions")) {
                if (auto func_symbol = std::dynamic_pointer_cast<Symbols::FunctionSymbol>(symbol_ptr)) {
                    // TODO: A függvény hívását kellene feldolgozni, a func_symbol-ból kellene lekérni a paramétereket, func_symbol->plainBody() tartalmazza a függvény törzsét
                    // A függvény hívásának feldolgozása
                    std::cout << "Function call: " << token.value << "\n";
                    while (consumeToken().lexeme != ")") {
                        // Feltételezzük, hogy a függvény hívását a lexer már feldolgozta
                    }
                    return Symbols::Value("");  // TODO: Implementálni a függvény hívását
                }
            }
        }

        bool is_negative = false;
        std::cout << "Peek: " << peekToken().lexeme << "\n";
        if (token.type == Lexer::Tokens::Type::OPERATOR_ARITHMETIC && peekToken().type == Lexer::Tokens::Type::NUMBER) {
            is_negative = true;
        // Előjel kezelése
        if (token.type == Lexer::Tokens::Type::OPERATOR_ARITHMETIC && (token.lexeme == "-" || token.lexeme == "+") &&
            peekToken().type == Lexer::Tokens::Type::NUMBER) {
            is_negative = (token.lexeme == "-");
            token       = peekToken();
            consumeToken();
            consumeToken();  // előjelet elfogyasztottuk
        }

        // STRING típus
        if (expected_var_type == Symbols::Variables::Type::STRING) {
            if (token.type == Lexer::Tokens::Type::STRING_LITERAL) {
                consumeToken();
                return Symbols::Value(token.value);  // A lexer value-ja már a feldolgozott string
                return Symbols::Value(token.value);
            }
            reportError("Expected string literal value");
        } else if (expected_var_type == Symbols::Variables::Type::INTEGER) {
            if (token.type == Lexer::Tokens::Type::NUMBER) {
                // Konvertálás int-re, hibakezeléssel
                try {
                    // TODO: Ellenőrizni, hogy a szám valóban egész-e (nincs benne '.')
                    // Most egyszerűen std::stoi-t használunk.
                    int int_value = std::stoi(token.value);
                    if (is_negative) {
                        int_value = -int_value;
                    }
                    consumeToken();
                    return Symbols::Value(int_value);
                } catch (const std::invalid_argument & e) {
                    reportError("Invalid integer literal: " + token.value);
                } catch (const std::out_of_range & e) {
                    reportError("Integer literal out of range: " + token.value);
                }
            }
            reportError("Expected integer literal value");
        } else if (expected_var_type == Symbols::Variables::Type::DOUBLE) {
            if (token.type == Lexer::Tokens::Type::NUMBER) {
                // Konvertálás double-re, hibakezeléssel
                try {
                    double double_value = std::stod(token.value);
                    if (is_negative) {
                        double_value = -double_value;
                    }
                    consumeToken();
                    return Symbols::Value(double_value);
                } catch (const std::invalid_argument & e) {
                    reportError("Invalid double literal: " + token.value);
                } catch (const std::out_of_range & e) {
                    reportError("Double literal out of range: " + token.value);
                }
            }
            reportError("Expected numeric literal value for double");
        } else if (expected_var_type == Symbols::Variables::Type::FLOAT) {
            if (token.type == Lexer::Tokens::Type::NUMBER) {
                // Konvertálás double-re, hibakezeléssel
                try {

                    float float_value = std::atof(token.value.data());
                    if (is_negative) {
                        float_value = -float_value;
                    }
                    consumeToken();
                    return Symbols::Value(float_value);
                } catch (const std::invalid_argument & e) {
                    reportError("Invalid float literal: " + token.value);
                } catch (const std::out_of_range & e) {
                    reportError("Float literal out of range: " + token.value);
                }
            }
            reportError("Expected numeric literal value for double");
        } else if (expected_var_type == Symbols::Variables::Type::BOOLEAN) {
            if (token.type == Lexer::Tokens::Type::KEYWORD) {
                consumeToken();
                return Symbols::Value(token.value == "true");  // A lexer value-ja már a feldolgozott string
            }
            reportError("Expected boolean literal value");
        } else {
            // Más típusok (pl. boolean) itt kezelendők, ha lennének
            reportError("Unsupported variable type encountered during value parsing");
        }
        // Should not reach here due to reportError throwing
        return Symbols::Value();  // Default return to satisfy compiler

        // BOOLEAN típus
        if (expected_var_type == Symbols::Variables::Type::BOOLEAN) {
            if (token.type == Lexer::Tokens::Type::KEYWORD && (token.value == "true" || token.value == "false")) {
                consumeToken();
                return Symbols::Value(token.value == "true");
            }
            reportError("Expected boolean literal value (true or false)");
        }

        // NUMERIC típusok
        if (expected_var_type == Symbols::Variables::Type::INTEGER ||
            expected_var_type == Symbols::Variables::Type::DOUBLE ||
            expected_var_type == Symbols::Variables::Type::FLOAT) {
            if (token.type == Lexer::Tokens::Type::NUMBER) {
                Symbols::Value val = parseNumericLiteral(token.value, is_negative, expected_var_type);
                consumeToken();
                return val;
            }

            reportError("Expected numeric literal value");
        }

        reportError("Unsupported variable type encountered during value parsing");
        return Symbols::Value();  // compiler happy
    }

    Symbols::SymbolContainer parseFunctionBody(const Lexer::Tokens::Token & opening_brace,
                                               bool                         return_required = false) {
    Symbols::Value parseNumericLiteral(const std::string & value, bool is_negative, Symbols::Variables::Type type) {
        try {
            switch (type) {
                case Symbols::Variables::Type::INTEGER:
                    {
                        if (value.find('.') != std::string::npos) {
                            throw std::invalid_argument("Floating point value in integer context: " + value);
                        }
                        int v = std::stoi(value);
                        return Symbols::Value(is_negative ? -v : v);
                    }
                case Symbols::Variables::Type::DOUBLE:
                    {
                        double v = std::stod(value);
                        return Symbols::Value(is_negative ? -v : v);
                    }
                case Symbols::Variables::Type::FLOAT:
                    {
                        float v = std::stof(value);
                        return Symbols::Value(is_negative ? -v : v);
                    }
                default:
                    throw std::invalid_argument("Unsupported numeric type");
            }
        } catch (const std::invalid_argument & e) {
            reportError("Invalid numeric literal: " + value + " (" + e.what() + ")");
        } catch (const std::out_of_range & e) {
            reportError("Numeric literal out of range: " + value + " (" + e.what() + ")");
        }

        return Symbols::Value();  // unreachable
    }

    void parseFunctionBody(const Lexer::Tokens::Token & opening_brace, const std::string & function_name,
                           Symbols::Variables::Type return_type, const Symbols::FunctionParameterInfo & params) {
        size_t               braceDepth = 0;
        int                  peek       = 0;
        int                  tokenIndex = current_token_index_;
        Lexer::Tokens::Token currentToken_;
        Lexer::Tokens::Token closing_brace;

        while (tokenIndex < tokens_.size()) {
            currentToken_ = peekToken();

            currentToken_ = peekToken(peek);
            if (currentToken_.type == Lexer::Tokens::Type::PUNCTUATION) {
                if (currentToken_.value == "{") {
                    ++braceDepth;
@@ -460,6 +387,8 @@
                    --braceDepth;
                }
            }
            tokenIndex++;
            peek++;
        }
        if (braceDepth != 0) {
            reportError("Unmatched braces in function body");
@@ -468,65 +397,190 @@
        auto                              startIt = std::find(tokens_.begin(), tokens_.end(), opening_brace);
        auto                              endIt   = std::find(tokens_.begin(), tokens_.end(), closing_brace);

        // Ellenőrzés: mindkét token megtalálva és start_token megelőzi az end_token-t
        if (startIt != tokens_.end() && endIt != tokens_.end() && startIt < endIt) {
            filtered_tokens = std::vector<Lexer::Tokens::Token>(startIt + 1, endIt);
        }
        std::string_view input_string = input_str_view_.substr(opening_brace.end_pos, closing_brace.end_pos);
        auto             parser       = Parser();
        parser.parseProgram(filtered_tokens, input_string);

        return *parser.getSymbolContainer();
        current_token_index_ = tokenIndex;
        expect(Lexer::Tokens::Type::PUNCTUATION, "}");
        const std::string newns = Symbols::SymbolContainer::instance()->currentScopeName() + "." + function_name;
        Symbols::SymbolContainer::instance()->create(newns);
        std::shared_ptr<Parser> parser = std::make_shared<Parser>();
        parser->parseScript(filtered_tokens, input_string, this->current_filename_);
        Symbols::SymbolContainer::instance()->enterPreviousScope();
        // create function
        Interpreter::OperationsFactory::defineFunction(
            function_name, params, return_type, Symbols::SymbolContainer::instance()->currentScopeName(),
            this->current_filename_, currentToken_.line_number, currentToken_.column_number);
    }

    std::string parseFunctionBodyOld(size_t body_start_pos, bool return_required = false) {
        std::stringstream body_ss;
        int               brace_level        = 1;
        size_t            last_token_end_pos = body_start_pos;
        bool              has_return         = false;
    ParsedExpressionPtr parseParsedExpression(const Symbols::Variables::Type & expected_var_type) {
        std::stack<std::string>          operator_stack;
        std::vector<ParsedExpressionPtr> output_queue;

        auto getPrecedence = [](const std::string & op) -> int {
            if (op == "+" || op == "-") {
                return 1;
            }
            if (op == "*" || op == "/") {
                return 2;
            }
            if (op == "u-" || op == "u+") {
                return 3;
            }
            return 0;
        };

        auto isLeftAssociative = [](const std::string & op) -> bool {
            return !(op == "u-" || op == "u+");
        };

        auto applyOperator = [](const std::string & op, ParsedExpressionPtr rhs, ParsedExpressionPtr lhs = nullptr) {
            if (op == "u-" || op == "u+") {
                std::string real_op = (op == "u-") ? "-" : "+";
                return ParsedExpression::makeUnary(real_op, std::move(rhs));
            } else {
                return ParsedExpression::makeBinary(op, std::move(lhs), std::move(rhs));
            }
        };

        auto pushOperand = [&](const Lexer::Tokens::Token & token) {
            if (token.type == Lexer::Tokens::Type::NUMBER || token.type == Lexer::Tokens::Type::STRING_LITERAL ||
                token.type == Lexer::Tokens::Type::KEYWORD) {
                output_queue.push_back(
                    ParsedExpression::makeLiteral(Symbols::Value::fromString(token.value, expected_var_type)));
            } else if (token.type == Lexer::Tokens::Type::VARIABLE_IDENTIFIER) {
                std::string name = token.value;
                if (!name.empty() && name[0] == '$') {
                    name = name.substr(1);
                }
                output_queue.push_back(ParsedExpression::makeVariable(name));
            } else {
                reportError("Expected literal or variable");
            }
        };

        bool expect_unary = true;

        while (true) {
            if (isAtEnd()) {
                reportError("Unexpected end of file inside function body (missing '}')");
            }
            const auto & token = currentToken();
            auto token = currentToken();

            // Whitespace visszaállítása (ha volt) az 'input_str_view_' alapján
            if (token.start_pos > last_token_end_pos) {
                if (last_token_end_pos < input_str_view_.length() && token.start_pos <= input_str_view_.length()) {
                    body_ss << input_str_view_.substr(last_token_end_pos, token.start_pos - last_token_end_pos);
                } else {
                    reportError("Invalid position range in body reconstruction");
            if (token.type == Lexer::Tokens::Type::PUNCTUATION && token.lexeme == "(") {
                operator_stack.push("(");
                consumeToken();
                expect_unary = true;
            } else if (token.type == Lexer::Tokens::Type::PUNCTUATION && token.lexeme == ")") {
                consumeToken();
                while (!operator_stack.empty() && operator_stack.top() != "(") {
                    std::string op = operator_stack.top();
                    operator_stack.pop();

                    if (op == "u-" || op == "u+") {
                        if (output_queue.empty()) {
                            reportError("Missing operand for unary operator");
                        }
                        auto rhs = std::move(output_queue.back());
                        output_queue.pop_back();
                        output_queue.push_back(applyOperator(op, std::move(rhs)));
                    } else {
                        if (output_queue.size() < 2) {
                            reportError("Malformed expression");
                        }
                        auto rhs = std::move(output_queue.back());
                        output_queue.pop_back();
                        auto lhs = std::move(output_queue.back());
                        output_queue.pop_back();
                        output_queue.push_back(applyOperator(op, std::move(rhs), std::move(lhs)));
                    }
                }
            }

            if (token.type == Lexer::Tokens::Type::KEYWORD_RETURN) {
                has_return = true;
            }

            if (token.type == Lexer::Tokens::Type::PUNCTUATION && token.value == "{") {
                brace_level++;
                body_ss << token.lexeme;
            } else if (token.type == Lexer::Tokens::Type::PUNCTUATION && token.value == "}") {
                brace_level--;
                if (brace_level == 0) {
                    consumeToken();  // Záró '}' elfogyasztása
                    break;
                if (operator_stack.empty() || operator_stack.top() != "(") {
                    reportError("Mismatched parentheses");
                }
                body_ss << token.lexeme;
                operator_stack.pop();  // remove "("
                expect_unary = false;
            } else if (token.type == Lexer::Tokens::Type::OPERATOR_ARITHMETIC) {
                std::string op = std::string(token.lexeme);
                if (expect_unary && (op == "-" || op == "+")) {
                    op = "u" + op;  // pl. u-
                }

                while (!operator_stack.empty()) {
                    const std::string & top = operator_stack.top();
                    if ((isLeftAssociative(op) && getPrecedence(op) <= getPrecedence(top)) ||
                        (!isLeftAssociative(op) && getPrecedence(op) < getPrecedence(top))) {
                        operator_stack.pop();

                        if (top == "u-" || top == "u+") {
                            if (output_queue.empty()) {
                                reportError("Missing operand for unary operator");
                            }
                            auto rhs = std::move(output_queue.back());
                            output_queue.pop_back();
                            output_queue.push_back(applyOperator(top, std::move(rhs)));
                        } else {
                            if (output_queue.size() < 2) {
                                reportError("Malformed expression");
                            }
                            auto rhs = std::move(output_queue.back());
                            output_queue.pop_back();
                            auto lhs = std::move(output_queue.back());
                            output_queue.pop_back();
                            output_queue.push_back(applyOperator(top, std::move(rhs), std::move(lhs)));
                        }
                    } else {
                        break;
                    }
                }

                operator_stack.push(op);
                consumeToken();
                expect_unary = true;
            } else if (token.type == Lexer::Tokens::Type::NUMBER || token.type == Lexer::Tokens::Type::STRING_LITERAL ||
                       token.type == Lexer::Tokens::Type::KEYWORD ||
                       token.type == Lexer::Tokens::Type::VARIABLE_IDENTIFIER) {
                pushOperand(token);
                consumeToken();
                expect_unary = false;
            } else {
                body_ss << token.lexeme;
                break;
            }
        }

        // Kiürítjük az operator stack-et
        while (!operator_stack.empty()) {
            std::string op = operator_stack.top();
            operator_stack.pop();

            if (op == "(" || op == ")") {
                reportError("Mismatched parentheses");
            }

            last_token_end_pos = token.end_pos;
            consumeToken();
            if (op == "u-" || op == "u+") {
                if (output_queue.empty()) {
                    reportError("Missing operand for unary operator");
                }
                auto rhs = std::move(output_queue.back());
                output_queue.pop_back();
                output_queue.push_back(applyOperator(op, std::move(rhs)));
            } else {
                if (output_queue.size() < 2) {
                    reportError("Malformed expression");
                }
                auto rhs = std::move(output_queue.back());
                output_queue.pop_back();
                auto lhs = std::move(output_queue.back());
                output_queue.pop_back();
                output_queue.push_back(applyOperator(op, std::move(rhs), std::move(lhs)));
            }
        }

        if (return_required && !has_return) {
            return "";
        if (output_queue.size() != 1) {
            reportError("Expression could not be parsed cleanly");
        }

        return body_ss.str();
        return std::move(output_queue.back());
    }

};  // class Parser