In file included from /usr/local/include/boost-1_45/boost/proto/core.hpp:26:0,
                 from /Users/joelfalcou/nt2/sandbox/foo.cpp:12:
/usr/local/include/boost-1_45/boost/proto/operators.hpp: In instantiation of 'boost::proto::detail::enable_binary<calculator_domain, boost::proto::_, boost::mpl::or_<boost::proto::is_extension<void>, boost::proto::is_extension<calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l> > >, mpl_::bool_<false>, mpl_::bool_<false>, mpl_::bool_<false> >, boost::proto::tag::comma, void, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l> > >':
/usr/local/include/boost-1_45/boost/proto/operators.hpp:93:9:   instantiated from 'boost::proto::detail::enable_binary<boost::proto::domainns_::deduce_domain, boost::proto::detail::not_a_grammar, boost::mpl::or_<boost::proto::is_extension<void>, boost::proto::is_extension<calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l> > >, mpl_::bool_<false>, mpl_::bool_<false>, mpl_::bool_<false> >, boost::proto::tag::comma, void, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l> > >'
/usr/local/include/boost-1_45/boost/proto/matches.hpp:978:96:   instantiated from 'boost::proto::detail::_and_impl<boost::proto::and_<G0, G1>, Expr, State, Data>::result_type boost::proto::detail::_and_impl<boost::proto::and_<G0, G1>, Expr, State, Data>::operator()(typename boost::proto::detail::_and_impl<boost::proto::and_<G0, G1>, Expr, State, Data>::expr_param, typename boost::proto::detail::_and_impl<boost::proto::and_<G0, G1>, Expr, State, Data>::state_param, typename boost::proto::detail::_and_impl<boost::proto::and_<G0, G1>, Expr, State, Data>::data_param) const [with G0 = print_tag(boost::proto::_), G1 = boost::proto::generator<calculator_expression>(boost::proto::_), Expr = const boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l>&, State = int, Data = int, boost::proto::detail::_and_impl<boost::proto::and_<G0, G1>, Expr, State, Data>::result_type = calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l> >, typename boost::proto::detail::_and_impl<boost::proto::and_<G0, G1>, Expr, State, Data>::expr_param = const boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l>&, typename boost::proto::detail::_and_impl<boost::proto::and_<G0, G1>, Expr, State, Data>::state_param = const int&, typename boost::proto::detail::_and_impl<boost::proto::and_<G0, G1>, Expr, State, Data>::data_param = const int&]'
/usr/local/include/boost-1_45/boost/proto/transform/impl.hpp:96:9:   instantiated from 'typename boost::proto::detail::apply_transform<PrimitiveTransform(Expr&)>::result_type boost::proto::transform<PrimitiveTransform, X>::operator()(Expr&) const [with Expr = const boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l>, PrimitiveTransform = boost::proto::and_<print_tag(boost::proto::_), boost::proto::generator<calculator_expression>(boost::proto::_), void, void, void, void, void, void>, X = void, typename boost::proto::detail::apply_transform<PrimitiveTransform(Expr&)>::result_type = calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l> >]'
/usr/local/include/boost-1_45/boost/proto/make_expr.hpp:744:46:   instantiated from 'boost::proto::detail::make_expr_<Tag, Domain, A0, A1, void, void, void, void>::result_type boost::proto::detail::make_expr_<Tag, Domain, A0, A1, void, void, void, void>::operator()(typename boost::add_reference<T2>::type, typename boost::add_reference<T3>::type) const [with Tag = boost::proto::tag::plus, Domain = calculator_domain, A0 = const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, A1 = const double&, boost::proto::detail::make_expr_<Tag, Domain, A0, A1, void, void, void, void>::result_type = calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l> >, typename boost::add_reference<T2>::type = const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, typename boost::add_reference<T3>::type = const double&]'
/usr/local/include/boost-1_45/boost/proto/operators.hpp:241:1:   instantiated from 'const typename boost::proto::detail::enable_binary<boost::proto::domainns_::deduce_domain, boost::proto::detail::not_a_grammar, boost::mpl::or_<boost::proto::is_extension<Arg>, boost::proto::is_extension<Right> >, boost::proto::tag::plus, const Left, const Right>::type boost::proto::exprns_::operator+(const Left&, const Right&) [with Left = calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >, Right = double, typename boost::proto::detail::enable_binary<boost::proto::domainns_::deduce_domain, boost::proto::detail::not_a_grammar, boost::mpl::or_<boost::proto::is_extension<Arg>, boost::proto::is_extension<Right> >, boost::proto::tag::plus, const Left, const Right>::type = calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::plus, boost::proto::argsns_::list2<const calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<placeholder<1> >, 0l> >&, calculator_expression<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<const double&>, 0l> > >, 2l> >]'
/Users/joelfalcou/nt2/sandbox/foo.cpp:129:24:   instantiated from here
/usr/local/include/boost-1_45/boost/proto/operators.hpp:81:9: error: forming reference to void