C++ TokenStream::getToken方法代码示例

double expression(TokenStream& tokenStream)
{
    double result = term(tokenStream);       // set result to value of term
    Token token = tokenStream.getToken();  // get next token from tokenStream

    while (true)
    {
        if (token.kind == '+')
        {
            result += term(tokenStream);      // evaluate term and add to result
            token = tokenStream.getToken(); // get next token from tokenStream
        }

        if (token.kind == '-')
        {
            result -= term(tokenStream);      // evaluate term and subtract from result
            token = tokenStream.getToken(); // get next token from tokenStream
        }

        if (token.kind != '+' && token.kind != '-')
        {
            tokenStream.setToken(token);    // reset token into token stream
            return result;                    // return result
        }
    }
}

void calculate()
{
    const char quit = 'q';       // t.kind==quit means that t is a quit Token
    const char print = ';';      // t.kind==print means that t is a print Token
    const std::string prompt = "> ";
    const std::string equals = "= ";  // used to indicate that what follows is an evaluation
    TokenStream tokenStream;
    std::string enterToClose = "~~";

    while (std::cin)
        try
        {
            std::cout << prompt;
            Token token = tokenStream.getToken();

            if (token.kind == print)
                token = tokenStream.getToken();   // eat ';'

            if (token.kind == quit)
                break;

            tokenStream.setToken(token);      // reset token into tokenStream
            std::cout << equals << expression(tokenStream) << '\n';
        }

        catch (std::exception& e)
        {
            std::cerr << e.what() << '\n';                      // write error message
            tokenStream.ignore(print);
        }
}

double primary(TokenStream& tokenStream)
{
    const char number = '8';

    Token token = tokenStream.getToken();

    if (token.kind == '-') return -primary(tokenStream);

    else if (token.kind == '+') return primary(tokenStream);

    else if (token.kind == number) return token.value; // return the number’s value

    else if (token.kind == '(') // handle ‘(‘ expression ‘)’
    {
        double result = expression(tokenStream);      // set result to value of expression
        token = tokenStream.getToken();               // get next token from tokenStream
        if (token.kind != ')') error("')' expected"); // check for error
        return result;                                // return divisor
    }

    else // check for error
        error("primary expected");
}

double term(TokenStream& tokenStream)
{
    double result = primary(tokenStream);   // set result to value of primary
    Token token = tokenStream.getToken(); // get next token from tokenStream

    while (true)
    {
        if (token.kind == '*')
        {
            result *= primary(tokenStream);   // evaluate primary and multiply with result
            token = tokenStream.getToken(); // get next token from tokenStream
        }

        else if (token.kind == '/')
        {
            double divisor = primary(tokenStream);     // set divisor to value of primary
            if (divisor == 0) error("divide by zero"); // check for error
            result /= divisor;                           // divide result by divisor
            token = tokenStream.getToken();      // get next token from tokenStream
        }

        else if (token.kind == '%') // modulo will only work on ints for this implementation
        {
            int numer = result; // cast result to int
            int denom = primary(tokenStream); // cast denom to int
            if (denom == 0) error("%: divide by zero"); // error check
            result = numer % denom; // get result
            token = tokenStream.getToken();      // get next token from tokenStream
        }

        else
        {
            tokenStream.setToken(token);   // put token back into the Token stream
            return result;                 // return result
        }
    }
}

TypeRef Parse_Type_Int(TokenStream& lex, bool allow_trait_list)
{
    //TRACE_FUNCTION;
    auto ps = lex.start_span();

    Token tok;

    switch( GET_TOK(tok, lex) )
    {
    case TOK_INTERPOLATED_TYPE:
        return mv$(tok.frag_type());
    // '!' - Only ever used as part of function prototypes, but is kinda a type... not allowed here though
    case TOK_EXCLAM:
        return TypeRef( Span(tok.get_pos()), TypeData::make_Bang({}) );
    // '_' = Wildcard (type inferrence variable)
    case TOK_UNDERSCORE:
        return TypeRef(Span(tok.get_pos()));

    // 'unsafe' - An unsafe function type
    case TOK_RWORD_UNSAFE:
    // 'extern' - A function type with an ABI
    case TOK_RWORD_EXTERN:
    // 'fn' - Rust function
    case TOK_RWORD_FN:
        PUTBACK(tok, lex);
        return Parse_Type_Fn(lex);

    case TOK_RWORD_IMPL:
        return Parse_Type_ErasedType(lex, allow_trait_list);

    // '<' - An associated type cast
    case TOK_LT:
    case TOK_DOUBLE_LT: {
        PUTBACK(tok, lex);
        auto path = Parse_Path(lex, PATH_GENERIC_TYPE);
        return TypeRef(TypeRef::TagPath(), lex.end_span(mv$(ps)), mv$(path));
        }
    //
    case TOK_RWORD_FOR: {
        auto hrls = Parse_HRB(lex);
        switch(LOOK_AHEAD(lex))
        {
        case TOK_RWORD_UNSAFE:
        case TOK_RWORD_EXTERN:
        case TOK_RWORD_FN:
            return Parse_Type_Fn(lex, hrls);
        default:
            return Parse_Type_Path(lex, hrls, true);
        }
        }
    // <ident> - Either a primitive, or a path
    case TOK_IDENT:
        if( lex.lookahead(0) == TOK_EXCLAM )
        {
            lex.getToken();
            // TODO: path macros
            return TypeRef(TypeRef::TagMacro(), Parse_MacroInvocation(ps, mv$(tok.str()), lex));
        }
        // or a primitive
        //if( auto ct = coretype_fromstring(tok.str()) )
        //{
        //    return TypeRef(TypeRef::TagPrimitive(), Span(tok.get_pos()), ct);
        //}
        PUTBACK(tok, lex);
        return Parse_Type_Path(lex, {}, allow_trait_list);
        // - Fall through to path handling
    // '::' - Absolute path
    case TOK_DOUBLE_COLON:
    // 'self' - This relative path
    case TOK_RWORD_SELF:
    // 'super' - Parent relative path
    case TOK_RWORD_SUPER:
    // ':path' fragment
    case TOK_INTERPOLATED_PATH:
        PUTBACK(tok, lex);
        return Parse_Type_Path(lex, {}, allow_trait_list);

    // HACK! Convert && into & &
    case TOK_DOUBLE_AMP:
        lex.putback(Token(TOK_AMP));
    // '&' - Reference type
    case TOK_AMP: {
        AST::LifetimeRef lifetime;
        // Reference
        tok = lex.getToken();
        if( tok.type() == TOK_LIFETIME ) {
            lifetime = AST::LifetimeRef(/*lex.point_span(), */lex.get_ident(::std::move(tok)));
            tok = lex.getToken();
        }
        bool is_mut = false;
        if( tok.type() == TOK_RWORD_MUT ) {
            is_mut = true;
        }
        else {
            PUTBACK(tok, lex);
        }
        return TypeRef(TypeRef::TagReference(), lex.end_span(mv$(ps)), ::std::move(lifetime), is_mut, Parse_Type(lex, false));
        }
    // '*' - Raw pointer
    case TOK_STAR:
//.........这里部分代码省略.........