Boost.Spirit X3 parser “no type named type in(…)”

I was toying with Boost.Spirit X3 calculator example when I encountered an error I couldn't get my head around.
I minimized the program to reduce complexity still throwing the same error. Say I want to parse an input as a list of statements (strings) followed by a delimiter (';').

This is my structure:

namespace client { namespace ast
 {    
     struct program
    {
        std::list<std::string> stmts;
    };
 }}

BOOST_FUSION_ADAPT_STRUCT(client::ast::program,
            (std::list<std::string>, stmts)
)

The grammar is as follows:

namespace client
{ 
    namespace grammar
    {

   x3::rule<class program, ast::program> const program("program");

    auto const program_def =
            *((*char_) > ';')
            ;

   BOOST_SPIRIT_DEFINE(
       program
    );
    auto calculator = program;
}

using grammar::calculator;

}

Invoked

    int
    main()
    {
    std::cout <<"///////////////////////////////////////////\n\n";
    std::cout << "Expression parser...\n\n";
    std::cout << //////////////////////////////////////////////////\n\n";
    std::cout << "Type an expression...or [q or Q] to quit\n\n";

    typedef std::string::const_iterator iterator_type;
    typedef client::ast::program ast_program;

    std::string str;
    while (std::getline(std::cin, str))
    {
        if (str.empty() || str[0] == 'q' || str[0] == 'Q')
            break;

        auto& calc = client::calculator;    // Our grammar
        ast_program program;                // Our program (AST)

        iterator_type iter = str.begin();
        iterator_type end = str.end();
        boost::spirit::x3::ascii::space_type space;
        bool r = phrase_parse(iter, end, calc, space, program);

        if (r && iter == end)
        {
            std::cout << "-------------------------\n";
            std::cout << "Parsing succeeded\n";
            std::cout<< '\n';
            std::cout << "-------------------------\n";
        }
        else
        {
            std::cout << "-------------------------\n";
            std::cout << "Parsing failed\n";
            std::cout << "-------------------------\n";
        }
    }

    std::cout << "Bye... :-) \n\n";
    return 0;
}

Error I get is

/opt/boost_1_66_0/boost/spirit/home/x3/support/traits/container_traits.hpp: In instantiation of ‘struct boost::spirit::x3::traits::container_value<client::ast::program, void>’:
.
.
.

/opt/boost_1_66_0/boost/spirit/home/x3/support/traits/container_traits.hpp:76:12: error: no type named ‘value_type’ in ‘struct client::ast::program’
         struct container_value
/opt/boost_1_66_0/boost/spirit/home/x3/operator/detail/sequence.hpp:497:72: error: no type named ‘type’ in ‘struct boost::spirit::x3::traits::container_value<client::ast::program, void>’
          , typename traits::is_substitute<attribute_type, value_type>::type());
                                                                        ^~~~~~

Things I tried:

Following Getting boost::spirit::qi to use stl containers
Even though it uses Qi I nonetheless tried:

namespace boost{namespace spirit{ namespace traits{
template<>
struct container_value<client::ast::program> 
//also with struct container<client::ast::program, void>
{
      typedef std::list<std::string> type;
};
}}}

You see I'm kinda in the dark, so expectably to no avail.

parser2.cpp:41:8: error: ‘container_value’ is not a class template
 struct container_value<client::ast::program>
        ^~~~~~~~~~~~~~~

In the same SO question I author says
"There is one known limitation though, when you try to use a struct that has a single element that is also a container compilation fails unless you add qi::eps >> ... to your rule."

I did try adding a dummy eps also without success.

Please, help me decipher what that error means.

Yup. This looks like another limitation with automatic propagation of attributes when single-element sequences are involved.

I'd probably bite the bullet and change the rule definition from what it is (and what you'd expect to work) to:

x3::rule<class program_, std::vector<std::string> >

That removes the root of the confusion.

Other notes:

you had char_ which also eats ';' so the grammar would never succeed because no ';' would follow a "statement".
your statements aren't lexeme, so whitespace is discarded (is this what you meant? See Boost spirit skipper issues)
your statement could be empty, which meant parsing would ALWAYS fail at the end of input (where it would always read an empty state, and then discover that the expected ';' was missing). Fix it by requiring at least 1 character before accepting a statement.

With some simplifications/style changes:

Live On Coliru

#include <boost/fusion/adapted.hpp>
#include <boost/spirit/home/x3.hpp>
#include <list>

namespace x3 = boost::spirit::x3;

namespace ast {
    using statement = std::string;

    struct program {
        std::list<statement> stmts;
    };
} 

BOOST_FUSION_ADAPT_STRUCT(ast::program, stmts)

namespace grammar {
    auto statement 
        = x3::rule<class statement_, ast::statement> {"statement"}
        = +~x3::char_(';');
    auto program 
        = x3::rule<class program_, std::list<ast::statement> > {"program"}
        = *(statement >> ';');
} 

#include <iostream>
#include <iomanip>

int main() {
    std::cout << "Type an expression...or [q or Q] to quit\n\n";

    using It = std::string::const_iterator;

    for (std::string str; std::getline(std::cin, str);) {
        if (str.empty() || str[0] == 'q' || str[0] == 'Q')
            break;

        auto &parser = grammar::program;
        ast::program program; // Our program (AST)

        It iter = str.begin(), end = str.end();
        if (phrase_parse(iter, end, parser, x3::space, program)) {
            std::cout << "Parsing succeeded\n";
            for (auto& s : program.stmts) {
                std::cout << "Statement: " << std::quoted(s, '\'') << "\n";
            }
        }
        else
            std::cout << "Parsing failed\n";

        if (iter != end)
            std::cout << "Remaining unparsed: " << std::quoted(std::string(iter, end), '\'') << "\n";
    }
}

Which for input "a;b;c;d;" prints:

Parsing succeeded
Statement: 'a'
Statement: 'b'
Statement: 'c'
Statement: 'd'

来源：https://stackoverflow.com/questions/50252680/boost-spirit-x3-parser-no-type-named-type-in

标签

c++

parsing

boost-spirit