Hi Eric Thanks for all the help so far. I'm now filling out my prototype if/else implementation, mainly following your excellent recipe, and I've encountered a little annoyance. If I write an expression like: _1 + _2 ADL finds all the necessary operators etc in boost::proto (_1 and _2 are my placeholders in the phoenix namespace, using your extends mechanism), so it can built the right expression tree. All good so far. If I now write: if_(_1 == _2)[stuff...] // stuff... is unimportant Unfortunately proto::if_ is pulled in. This means I have to qualify phoenix::if_, which looks a bit too verbose for a lambda library. I think this could be addressed by moving the stuff that does not pertain to expression tree generation out of the boost::proto namespace, and into another boost::proto::other_stuff namespace, so the chances of it being pulled during tree construction are reduced, and I can have my unqualified syntax back. Is this possible? Or have I missed something on my side that could prevent this happening? Cheers Dan ___________________________________________________________ Yahoo! Answers - Got a question? Someone out there knows the answer. Try it now. http://uk.answers.yahoo.com/