递归下降与递归上升解析

如果我正在编写自己的自定义解析器，我如何知道我是否正在编写递归上升解析器?我确实对LALR解析的O(n)复杂性感兴趣(加上我已经有了LALR语法)，并且不想以后发现我已经编写了一个LL解析器。

编辑:我只见过自动表驱动解析器和几个生成的简单递归解析器示例-它们看起来都不像我手工构建的任何东西。因此，很难将处理规则的"明显"代码与实际算法联系起来。

如果您将代码用于一个相对简单的规则，例如

name_or_qualified_name = identifier *('.' identifier);

我把它翻译成

std::vector<std::wstring> RecursiveParseNameOrQualifiedName(Iterator& begin, Iterator end) {
    std::vector<std::wstring> retval;
    retval.push_back(begin->Codepoints);
    CheckedIncrement(begin, end); // The only place that can legitimately expect end of input is namespace contents.
    while(begin->type == Wide::Lexer::TokenType::Dot) {
        CheckedIncrement(begin, end);
        if (begin->type != Wide::Lexer::TokenType::Identifier)
            Wide::ParserExceptionBuilder(*begin) << L"Expected 'identifier' after '.'";
        retval.push_back(begin->Codepoints);
    }
    return retval;
}

没有什么非常左或右的。这显然是有用且重要的信息，但我没有看到。这里唯一明显的事实是它是递归的。

编辑:对不起，坏的例子。不如这样写:

void RecursiveParseUsing(Iterator& begin, Iterator end, Wide::Parser::NamespaceAST* current_namespace) {
    auto new_using = std::unique_ptr<Wide::Parser::UsingAST>( new Wide::Parser::UsingAST() );
    // expect "begin" to point to a using
    CheckedIncrement(begin, end);
    // Must be an identifier, at least
    if (begin->type != Wide::Lexer::TokenType::Identifier)
        Wide::ParserExceptionBuilder(*begin) << L"Expected 'identifier' after 'using'";
    CheckedIncrement(begin, end);
    switch(begin->type) {
    case Wide::Lexer::TokenType::Dot: {
        begin--; // back to identifier
        new_using->original_name = RecursiveParseNameOrQualifiedName(begin, end);
        current_namespace->unnamed_contents.push_back(std::move(new_using));
        break; }
    case Wide::Lexer::TokenType::Equals: {
        begin--; // back to Identifier
        new_using->new_name = begin->Codepoints;
        begin++; // Back to equals
        begin++; // The token ahead of equals- should be "identifier"
        new_using->original_name = RecursiveParseNameOrQualifiedName(begin, end); // The only valid next production
        // this should be left at the one past the name
        current_namespace->contents[new_using->new_name] = std::move(new_using);
        break; }
    case Wide::Lexer::TokenType::Semicolon: {
        begin--; // Identifier
        new_using->original_name.push_back(begin->Codepoints);
        begin++; // Semicolon
        current_namespace->unnamed_contents.push_back(std::move(new_using));
        break; }
    default:
        Wide::ParserExceptionBuilder(*begin) << L"Expected '.', '=' or ';' after 'identifier' when parsing 'using'.";
    }
    if (begin->type != Wide::Lexer::TokenType::Semicolon)
        Wide::ParserExceptionBuilder(*begin) << L"Expected ';' after 'identifier'";
    CheckedIncrement(begin, end); // One-past-the-end
}