I have a large number of custom unary and bin ary function that I map using unary_expr and binary_expr. The problem is the following : my grammar has integral or floating point scalar terminal. So, when I want to create a binary function that takes any elements of my domain, I'm boudn to do the following : template<class L,class R> typename result_of::make_expr<....>::type my_custom_binary_func( L const& l, R const& r ) { return make_expr( ... ); } Alas, as I already discussed with Eric, nothign prevent me to use my_custom_binary_func over types that aren't in my grammar. To do so, I was told to use SFINAE to prune unwanted element by matching the result type of make_expr on my grammar. However, this proves cumbersome and slow down compile time by *a large factor* when I have a large number of such function (and I have like 50 or 60). So i wandered into proto source code and looked at how proto solves this problem for its binary operator. This solution seems more elegant but as it live sin proto::detail, I don't think I'm intended to use it. So, how can I have a simple and fast creation of custom expression ? Am I missing something blatant ? -- ___________________________________________ Joel Falcou - Assistant Professor PARALL Team - LRI - Universite Paris Sud XI Tel : (+33)1 69 15 66 35