// In header: <boost/proto/traits.hpp>

struct right :  proto::callable {
  // member classes/structs/unions
  template<typename This, typename Expr> 
  struct result<This(Expr)> :  proto::result_of::right< Expr > {
  };
  // public member functions
  template<typename Expr> 
    typename proto::result_of::right< Expr & >::type operator()(Expr &) const;
  template<typename Expr> 
    typename proto::result_of::right< Expr const & >::type 
    operator()(Expr const &) const;
};