Problem with Boost.Phoenix custom terminal

// Compile with: g++ -std=gnu++0x -I. -o terminal_test ./terminal_test.cpp

#include <string>
#include <iostream>
#include <boost/phoenix.hpp>
#include <boost/function.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/utility/result_of.hpp>
#include <boost/type_traits/remove_cv.hpp>
#include <boost/type_traits/remove_reference.hpp>

using namespace boost;

namespace boost {

namespace phoenix {

namespace result_of {

template< typename T >
struct is_nullary< T, typename T::_is_my_terminal > :
    public mpl::false_
{
};

} // namespace result_of

template< typename T >
struct is_custom_terminal< T, typename T::_is_my_terminal > :
    public mpl::true_
{
};

template< typename T >
struct custom_terminal< T, typename T::_is_my_terminal >
{
    typedef custom_terminal< T, typename T::_is_my_terminal > this_type;

    template< typename >
    struct result;

    template< typename ThisT, typename TermT, typename ContextT >
    struct result< ThisT(TermT, ContextT) >
    {
        typedef typename remove_cv< typename remove_reference< TermT >::type >::type term;
        typedef typename boost::result_of< const term(ContextT) >::type type;
    };

    template< typename ContextT >
    typename result< const this_type(T, ContextT) >::type operator() (T const& term, ContextT& ctx) const
    {
        return term(ctx);
    }
};

} // namespace phoenix

} // namespace boost

namespace my {

struct argument
{
    std::string m_value;

    explicit argument(std::string const& value) : m_value(value)
    {
    }
};

template< typename LeftT >
class output_terminal
{
public:
    typedef void _is_my_terminal;

    //! Self type
    typedef output_terminal this_type;

    //! Result type definition
    template< typename >
    struct result;

    template< typename ContextT >
    struct result< this_type(ContextT) >
    {
        typedef typename remove_cv< typename remove_reference< ContextT >::type >::type context_type;
        typedef typename phoenix::evaluator::impl<
            typename LeftT::proto_base_expr&,
            context_type,
            phoenix::unused
        >::result_type type;
    };

    template< typename ContextT >
    struct result< const this_type(ContextT) >
    {
        typedef typename remove_cv< typename remove_reference< ContextT >::type >::type context_type;
        typedef typename phoenix::evaluator::impl<
            typename LeftT::proto_base_expr const&,
            context_type,
            phoenix::unused
        >::result_type type;
    };

private:
    //! Left argument actor
    LeftT m_left;
    //! Right argument
    std::string m_right;

public:
    //! Initializing constructor
    output_terminal(LeftT const& left, std::string const& right) : m_left(left), m_right(right)
    {
    }

    //! Invokation operator
    template< typename ContextT >
    typename result< this_type(ContextT) >::type operator() (ContextT const& ctx)
    {
        typedef typename result< this_type(ContextT) >::type result_type;
        result_type strm = phoenix::eval(m_left, ctx);
        strm << m_right;
        return strm;
    }

    //! Invokation operator
    template< typename ContextT >
    typename result< const this_type(ContextT) >::type operator() (ContextT const& ctx) const
    {
        typedef typename result< const this_type(ContextT) >::type result_type;
        result_type strm = phoenix::eval(m_left, ctx);
        strm << m_right;
        return strm;
    }
};

template< typename LeftExprT >
inline phoenix::actor< output_terminal< phoenix::actor< LeftExprT > > >
operator<< (phoenix::actor< LeftExprT > const& left, argument const& right)
{
    phoenix::actor< output_terminal< phoenix::actor< LeftExprT > > > res = { output_terminal< phoenix::actor< LeftExprT > >(left, right.m_value) };
    return res;
}

typedef phoenix::expression::argument< 1 >::type stream_type;
const stream_type stream = {};

} // namespace my

int main(int, char*[])
{
    function< void (std::ostream&) > func;

    func = my::operator<< (my::stream, my::argument("Hello, world!"));

    func(std::cout);

    return 0;
}