// In header: <boost/proto/transform/integral_c.hpp>
template<typename T, T I> 
struct integral_c :  proto::transform< integral_c< T, I > > {
  // member classes/structs/unions
  template<typename Expr, typename State, typename Data> 
  struct impl :  proto::transform_impl< Expr, State, Data > {
    // types
    typedef T result_type;
    // public member functions
    T operator()(typename impl::expr_param, typename impl::state_param, 
                 typename impl::data_param) const;
  };
};