Joel Falcou wrote:

I have a grammar with 3 kind of terminal : A,B and C. I want to have a transform that returns a mpl::int_ which is equal to the number of B terminal that appear in expression like :

A(B,B,C,B,C ..)

the grammar part for matching this is currently :

when< function< vargarg > , mpl::count< _, terminal<B> >() >

First, you want to use mpl::count_if with proto::matches so that you get the fuzzy terminal matching. Second, it seems that although proto expressions are valid Fusion sequences, they are not valid mpl sequences. That's a bug and I'll fix it. The following works for me: #include <iostream> #include #include #include namespace boost { namespace mpl { template struct sequence_tag< proto::expr > { typedef fusion::fusion_sequence_tag type; }; }} namespace mpl = boost::mpl; namespace proto = boost::proto; namespace fusion = boost::fusion; using proto::_; struct A {}; struct B {}; struct C {}; struct CountB : proto::when< proto::function< proto::vararg<_> > , mpl::count_if< _, proto::matches

...

() > {};

proto::terminal<A>::type a = {{}}; proto::terminal<B>::type b = {{}}; proto::terminal<C>::type c = {{}}; int main() { std::cout << CountB()( a(b,c,b,a) ) << std::endl; } HTH, -- Eric Niebler BoostPro Computing http://www.boostpro.com