Create a phoenix function for use in spirit rule

Question

I'm trying to make the code below compile, but, as usual, errors with spirit/phoenix gives not a lot a clues about what is wrong. Can anyone see what the problem is ?

#include <boost/spirit/include/phoenix.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/shared_ptr.hpp>


typedef boost::shared_ptr<int> sptr;


struct bar
{
    template <typename A> struct result
    {
        typedef sptr type;
    };

    template <typename A> sptr operator()(A) const
    {
        return sptr();
    }
};


boost::phoenix::function<bar> foo;


void test()
{
    namespace qi = boost::spirit::qi;
    using qi::_val;

    qi::rule
    <
        std::string::const_iterator,
        sptr(),
        boost::spirit::ascii::space_type
    >
        test_rule = qi::eps [ _val = foo() ];
}

Answer 1

As ildjarn said, call to foo misses an argument.