Hi all, i want to use the function proto::reverse_fold_tree to build a heterogeneous list from the expression "((a*b+c)*d+e)*f". The resulting sequence only contains the two terminals 'a' and b'. So i am a little bit confused. But using the function proto::fold_tree it produces correctly the sequence [f,e,d,c,b,a]. (Btw the two functions proto::fold_tree and proto::fold produce the same sequence [f,e,d,c,b,a], what is their difference? ) Here is the code: #include <iostream> #include <boost/proto/proto.hpp> #include <boost/proto/proto_typeof.hpp> #include <boost/fusion/container.hpp> #include <boost/fusion/algorithm/iteration.hpp> #include <boost/fusion/include/iteration.hpp> #include <boost/typeof/typeof.hpp> namespace mpl = boost::mpl; namespace proto = boost::proto; namespace fusion = boost::fusion; using proto::_; proto::terminal<char>::type const a = {'a'}; proto::terminal<char>::type const b = {'b'}; proto::terminal<char>::type const c = {'c'}; proto::terminal<char>::type const d = {'d'}; proto::terminal<char>::type const e = {'e'}; proto::terminal<char>::type const f = {'f'}; struct FoldToList : proto::or_< proto::when<proto::terminal<_>,fusion::cons<proto::_value, proto::_state>(proto::_value, proto::_state) > ,proto::when<proto::nary_expr<_,proto::vararg<_> >, proto::fold_tree<proto::_,fusion::nil(),FoldToList > > > {}; struct FoldToListReverse : proto::or_< proto::when<proto::terminal<_>,fusion::cons<proto::_value, proto::_state>(proto::_value, proto::_state) > ,proto::when<proto::nary_expr<_,proto::vararg<_> >, proto::reverse_fold_tree<proto::_,fusion::nil(),FoldToListReverse > > > {}; struct print { typedef void result_type; template<class T> result_type operator()(T const& t) const { std::cout<<t<<"\t"; } }; int main() { BOOST_PROTO_AUTO(expr, ((a*b+c)*d+e)*f ); proto::display_expr(expr); BOOST_MPL_ASSERT(( proto::matches<BOOST_TYPEOF(expr), FoldToList>)); BOOST_MPL_ASSERT(( proto::matches<BOOST_TYPEOF(expr), FoldToListReverse>)); BOOST_AUTO(sequence1,FoldToList()(expr)); fusion::for_each(sequence1,print()); std::cout << "\n--------------------\n"; BOOST_AUTO(sequence2,FoldToListReverse()(expr)); fusion::for_each(sequence2,print()); std::cout << "\n--------------------\n"; } Cheers Kim Tang