Includes Proto callable boost::proto::functional::at. A PolymorphicFunctionObject type that invokes the fusion::at() accessor function on its arguments. A PolymorphicFunctionObject type that invokes the fusion::at() accessor function on its arguments. proto::callable This(Seq, N) fusion::result_of::at< typename boost::remove_reference<Seq>::type , typename boost::remove_const<typename boost::remove_reference<N>::type>::type > typename fusion::result_of::at< Seq, N >::type Seq & N const & fusion::at<N>(seq) typename fusion::result_of::at< Seq const, N >::type Seq const & N const & fusion::at<N>(seq)