Joel Falcou wrote:

I have a nary_expr grammar rule and in its associated tranform, I want to retrieves the actual tag.

when< nary_expr<_ , bp::vararg > , some_transform_using_the_tag(bp::_tag) >

obviously proto::_tag doesn't exist. How can I retrieve this information ?

Well, there isn't a tag object, just a tag type. To get the tag's type in a transform, you can use proto::tag_of<_>. If you want a default-constructed object of that type, use proto::tag_of<_>(). HTH, -- Eric Niebler BoostPro Computing http://www.boostpro.com