#include <boost/phoenix.hpp>
#include <boost/spirit/include/karma.hpp>
#include <boost/fusion/include/adapt_struct.hpp>

struct foo {
    std::string a, b;
};

BOOST_FUSION_ADAPT_STRUCT(
    foo,
    (std::string, a)
    (std::string, b)
)

int main()
{
    using namespace boost::spirit::karma;
    using boost::phoenix::at_c;

    typedef rule<std::back_insert_iterator<std::string>, foo(), space_type>
        rule_t;

    rule_t r
        =   +char_ << '(' << string << ')'
        |   skip[string] << string
        ;

    foo f = {"a", "b"};
    std::string s;
    generate_delimited(std::back_inserter(s), r, space, f);
}