I just made a change to proto in the effort to reduce compile times. There's a new expression type, proto::basic_expr, that is lighter weight than proto::expr in that it doesn't define the operator=, operator[] and operator() member functions. It's ideal as a base when extending expressions with proto::extends or BOOST_PROTO_EXTENDS. You'll get basic_expr instead of expr automatically if you use either of proto::generator or proto::pod_generator. That could surprise you if you were expecting to get an expr, so beware. Most normal uses of Proto will just work with this change, though, and if you measure you should see a modest improvement in your compile times. Please let me know if this breaks your code. -- Eric Niebler BoostPro Computing http://www.boostpro.com