I am trying to create a transform where I replace occurrences of proto::terminal<term> with proto::terminal >. I want N to increment for every proto::terminal<term> encountered. So far I have the following code : #include #include #include #include <iostream> using namespace std; namespace proto=boost::proto; namespace mpl=boost::mpl; struct term {}; template<typename> struct newterm {}; proto::terminal<term>::type const a = {{}}; proto::terminal<term>::type const b = {{}}; proto::terminal<term>::type const c = {{}}; struct xform_callable : proto::callable { template<typename> struct result; template struct result { typedef typename proto::result_of::make_expr::type type; }; template struct result { typedef typename proto::result_of::make_expr::type type; }; template<typename N> typename proto::result_of::make_expr::type operator()(const term &, N) { return proto::make_exprproto::tag::terminal(newterm<N>()); } template typename proto::result_of::make_expr::type operator()(tag, LHS l, RHS r) const { return proto::make_expr<tag>(l, r); } }; struct xform : proto::or_< proto::when< proto::terminal<term>, xform_callable(proto::_value, mpl::nextproto::_state())>, proto::when< proto::plus, xform_callable(proto::tag_ofproto::_expr(), xform(proto::_left, proto::_state), xform(proto::_right, proto::_state))>

{}; int main() { mpl::plus, mpl::int_<1> >(); proto::display_expr(xform()(a+b/c, mpl::int_<0>())); return 0; } I pass in mpl::int_<0>() as the initial state and call mpl::next when I match proto::terminal<term>. As the output would indicate, this is not working. Every time I think I understand proto transforms, something basic like this stumps me. I will be grateful for any hints on how to accomplish this. Thanks, Manjunath