// In header: <boost/xpressive/regex_actions.hpp>


struct first {
  // member classes/structs/unions
  template<typename Sig> 
  struct result {
  };
  template<typename This, typename Pair> 
  struct result<This(Pair)> {
    // types
    typedef remove_reference< Pair >::type::first_type type;
  };

  // public member functions
  template<typename Pair> Pair::first_type operator()(Pair const &) const;
};