Hi, I am updating some of my code to use Phoenix3 instead of Phoenix2. For example in Phoenix2 I used to have this extension to support 'cos(...)' expressions: namespace boost{ namespace phoenix{ struct cos_eval{ template<class Env, typename Arg_> struct result{typedef double type;}; template<class RT, typename Env, typename Arg_> static RT eval(Env const& env, Arg_ const& arg_){ return cos(arg_.eval(env)); } }; template<typename Arg_> void cos(Arg_ const& arg_){ return compose<cos_eval>(arg_); } }} In Phoenix3, if I followed things correctly (from here https://svn.boost.org/svn/boost/sandbox/SOC/2010/phoenix3/libs/phoenix/doc/h...) the new framework ask for the following, which doesn't work. The error (see at end) is difficult to decipher. What am I missing to implement this simple expression extension? -- Thanks. #include<boost/phoenix/phoenix.hpp> //v3 BOOST_PHOENIX_DEFINE_EXPRESSION( (boost)(phoenix)(cos_) , (meta_grammar) // Arg ) namespace boost { namespace phoenix { struct cos_eval{ typedef double result_type; template <typename Context, typename Arg> result_type operator()(Context const& ctx, Arg const& arg) const{ return std::cos(eval(arg, ctx)); } }; template <typename Dummy> struct default_actions::when<rule::cos_, Dummy> : call<cos_eval, Dummy> {}; template <typename Arg> typename expression::cos_<Arg>::type const cos_(Arg const& arg){ return expression::cos_<Arg>::make(arg); } }} usr/include/boost/proto/matches.hpp:846:13: error: no type named ‘proto_tag’ in ‘const struct boost::phoenix::vector2<boost::phoenix::vector2<const boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::phoenix::tag::cos_, boost::proto::argsns_::list1<boost::phoenix::actor<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::phoenix::argument<1> >, 0l> > >, 1l> >*, double&>&, const boost::phoenix::default_actions&>’ compilation terminated due to -Wfatal-errors.