Accessing boost fusion map field name

I've been trying to use some of the boost fusion stuff to write a regular c struct to file. An XML file seems a good way to capture the data and make it compatible with other tools or hand editable. It seems like I almost have it but something fundamental seems to be missing. I'm using something pretty similar to what's on the boost::fusion quick start page: http://www.boost.org/doc/libs/1_54_0/libs/fusion/doc/html/fusion/quick_start.html. As a side note I have thoroughly looked here and on boost's documentation but no one seems to be accessing the field name.

struct print_xml
{
    template <typename T>
    void operator()(T const& x) const
    {
        std::cout
            << '<' << x.first << '>'
            << x
            << "</" << x.first << '>'
            ;
    }
};

I want to use it as follows:

BOOST_FUSION_ADAPT_STRUCT(
    myStructType,
    (double, val1)
    (double, val2)
    (char, letter)
    (int, number)
    )    
myStructType saveMe = { 3.4, 5.6, 'g', 9};
for_each(saveMe, print_xml());

Other times I defined the struct as follows, but still no luck:

namespace fields{
    struct val1;
    struct val2;
    struct letter;
    struct number;
}

typedef fusion::map<
    fusion::pair<fields::val1, double>,
    fusion::pair<fields::val2, double>,
    fusion::pair<fields::letter, char>,
    fusion::pair<fields::number, int> > myStructType;

I know there is no member first, but it really seems like there should be in order to access the field name! The code I have works fine with x.second but then doesn't accomplish what I need which is to get the field name. How else might I accomplish this? Thanks!