Is there anything obvious I'm doing wrong here? I'm using VC10 BTW, and big_number inherits from proto::terminal<big_number*> in case that makes any difference.
That last bit does make a difference. Proto grammar matching keys off the underlying proto expression type. So change this:
proto::terminal<boost::math::big_number<proto::_> >
to this:
proto::terminal<big_number*>
I assume you mean proto::terminal<big_number<proto::_>*> but I still get get the same error messages (the same with all the variations of the above I tried).
(Not sure exactly what you mean by "big_number inherits from proto::terminal<big_number*>. You clearly don't mean that. You mean either i/ big_number extends proto::terminal<big_number*>::type or ii/ big_number inherits from proto::terminal<big_number*>::type. Either way, the answer is the same.)
Ah yes, I meant proto::terminal<big_number<arg>*>::type. Also changed the grammar to use the proto::switch_, and yes that is better, well a bit anyway ;-) Thanks, John.