c – 模糊变体和提升精神x3

尝试调整boost精神x3 calc示例来解析可以将函数作为参数的函数.但是它没有编译.

namespace client{ namespace ast{
    struct ts;
    struct fnc;
    typedef boost::variant<
    ts,boost::recursive_wrapper<fnc>
    > node;
    struct ts{
        unsigned int id;
    };
    struct fnc{
        std::vector<char> id;
        std::vector<node> args;
    };
}}
BOOST_FUSION_ADAPT_STRUCT(
    client::ast::ts,(unsigned int,id)
)
BOOST_FUSION_ADAPT_STRUCT(
    client::ast::fnc,(std::vector<char>,id)
    (std::vector<client::ast::node>,args)
)
namespace client{
    namespace x3 = boost::spirit::x3;
    namespace calc_grammar{
        using x3::uint_;
        using x3::alpha;
        using x3::alnum;
        using x3::lit;
        using x3::char_;
        x3::rule<class funct,ast::fnc> const funct("function");
        x3::rule<class ts,ast::ts> const ts("timeseries");
        x3::rule<class funct_name,std::vector<char>> const funct_name("function_name");
        auto const funct_def = funct_name >> lit('(') >> -((ts|funct)%lit(',')) >> lit(')');
        auto const ts_def = lit('#') >> uint_ >> lit('#');
        auto const funct_name_def = lit('@') >> alpha >> *(alnum|char_('_'));
        auto const calc = x3::grammar(
            "calc",funct = funct_def,ts = ts_def,funct_name = funct_name_def
        );
    }
    using calc_grammar::calc;
}

error C2665: ‘boost::detail::variant::make_initializer_node::apply::initializer_node::initialize’: none of the 5 overloads Could convert all the argument types

在variant.hpp中还有一个用户注释

// NOTE TO USER :
// Compile error here indicates that the given type is not 
// unambiguously convertible to one of the variant's types
// (or that no conversion exists).

但我不是更聪明…

解决方法

我发现了这个老问题. X3在同一时间有所演变,尽管我现在也回答一下.

我怀疑主要问题可能与变体成员的(缺少)(隐式)构造函数一起使用.

无论如何,这是一个更轻巧的语法的现场演示：

namespace grammar_def {
    using namespace x3;

    rule<class funct,ast::fnc> const funct("function");

    auto const ts        = lexeme [ '#' >> uint_ >> '#' ];
    auto const fname     = lexeme [ '@' >> raw [ alpha >> *(alnum | '_') ] ];
    auto const expr      = ts|funct;

    auto const funct_def = fname >> '(' >> -expr % ',' >> ')';

    BOOST_SPIRIT_DEFINE(funct)
}

我还添加了一些输出流助手.请注意,为了简单起见,我如何将id类型更改为std :: string(在不侵入命名空间std的情况下重载运算符<<对于矢量< char>很难/不可能)：

namespace client { namespace ast {
    static std::ostream& operator<<(std::ostream& os,ts const& v) {
        using namespace boost::fusion;
        return os << tuple_open("") << tuple_close("") << tuple_delimiter("") << as_vector(v);
    }

    static std::ostream& operator<<(std::ostream& os,fnc const& v) {
        using namespace boost::fusion;
        return os << tuple_open("") << tuple_close("") << tuple_delimiter("") << as_vector(v);
    }
    template<typename T>
    static std::ostream& operator<<(std::ostream& os,std::vector<T> const& v) {
        os << "("; for (auto& el : v) os << (&el==&v[0]?"":",") << el; return os << ")";
    }
} }

演示

这有更多(可选)管道,以允许更丰富的调试信息：

Live On Coliru

//#define BOOST_SPIRIT_X3_DEBUG
#include <iostream>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/as_vector.hpp>
#include <boost/fusion/include/io.hpp>
#include <boost/spirit/home/x3.hpp>

namespace client { namespace ast {
    struct ts;
    struct fnc;

    //using string = std::vector<char>;
    using string = std::string; // for easier printing/debugging

    struct ts {
        unsigned int id;
        ts(unsigned id=0):id(id) {}
    };

    typedef boost::variant<ts,boost::recursive_wrapper<fnc> > node;

    struct fnc {
        string id;
        std::vector<node> args;
    };
} }

BOOST_FUSION_ADAPT_STRUCT(client::ast::ts,id)
BOOST_FUSION_ADAPT_STRUCT(client::ast::fnc,id,args)

//namespace std { static ostream& operator<<(ostream&os,vector<char> const& v) { return os.write(&v[0],v.size()); } }

namespace client { namespace ast {
    static std::ostream& operator<<(std::ostream& os,") << el; return os << ")";
    }
} }

namespace client {
    namespace x3 = boost::spirit::x3;
    namespace grammar_def {
        using namespace x3;

        x3::rule<class funct,ast::fnc> const funct("function");

        auto const ts     // = x3::rule<class ts,ast::ts> {"timeseries"}
                             = lexeme [ '#' >> uint_ >> '#' ];
        auto const fname  // = x3::rule<class fname,ast::string> {"function_name"}
                             = lexeme [ '@' >> raw [ alpha >> *(alnum | '_') ] ];
        auto const expr   // = rule<struct expr_,ast::node > {"expr"}
                             = ts|funct;

        auto const funct_def = fname >> '(' >> -expr % ',' >> ')';

        BOOST_SPIRIT_DEFINE(funct)
    }

    auto const& grammar = x3::skip(x3::space) [grammar_def::funct];
}

#include <iostream>

int main() {
    std::string const s {
        "@pow( #1#,\n"
            "     @trunc(\n"
            "           @pi ()\n"
            "   ) )"};
    std::cout << "Parsing '" << s << "'\n";

    auto f = s.begin();
    client::ast::fnc parsed;

    if (parse(f,s.end(),client::grammar,parsed)) {
        std::cout << "Parse succeeded: " << parsed << "\n";
    } else {
        std::cout << "Parse Failed\n";
    }

    if (f != s.end())
        std::cout << "Remaining unparsed input: '" << std::string(f,s.end()) << "'\n";
}

打印：

Parsing '@pow( #1#,@trunc(
           @pi ()
   ) )'
Parse succeeded: pow(1,trunc(pi()))

原文地址：https://www.jb51.cc/c/114853.html