The following fragments show what I think are the relevant parts of a file (which I can post if this doesn't explain the situation). For what I can tell, it is not too different from the lazy_vector example included with the documentation. I'd expect my_int<2> to match the grammar, but it doesn't. If I add proto::terminal<number<proto::_,proto::_> > as another term to the or, then I get a match. So it seems like the problem is with the "partial specialization" on two_complement_c and magnitude_c. Is there anything I have to do to them to make tham more "patternish". Thanks, Maurizio enum binary_representation_enum {magnitude, two_complement}; typedef mpl::integral_c<binary_representation_enum, magnitude> magnitude_c; typedef mpl::integral_c<binary_representation_enum, two_complement> two_complement_c; struct grammar : proto::or_ < proto::terminal<number<proto::_, two_complement_c> > , proto::terminal<number<proto::_, magnitude_c> >
{}; template<int N> struct my_int : my_expr<typename proto::terminal<number<mpl::int_<N>, two_complement_c > >::type> { ... }; template<typename Expr> void test (const Expr& expr) { if (proto::matches<Expr, grammar>::value) std::cout << "matches grammar\n\n"; else std::cout << "doesn't matches grammar\n\n"; } my_int<2> i2; test (i2);