I want to implement this: // returns whether Seq1 includes each of the elements in Seq2 // using Pred to determine type equality template<typename Seq1, // the putative superset typename Seq2, // the putative subset typename Pred> // whether T1 from Seq1 == T2 from Seq2 struct includes_if; My ultimate goal is to be able to determine whether every element in Seq2 is either in Seq1 or has a base class in Seq1. So the predicate I'll be passing in is a metafunction class that invokes std::tr1::is_base_of. Here's my code, all but one line of which is supposed to be correct: template<typename Seq1, // the putative superset typename Seq2, // the putative subset typename Pred> // whether T1 from Seq1 == T2 from Seq2 struct includes_if : boost::is_same< typename mpl::find_if< Seq2, mpl::not_<mpl::contains_if<Seq1, lambda(T) is_base_of<mpl::_1, T> //!! > > >::type, typename mpl::end<Seq2>::type
{}; The line I don't know how to write is flagged, but the functionality I want to express is shown. In case it's relevant, here is the rest of my code: // metafunction class for TR1-conforming is_base_of struct is_base_of { template<typename T1, typename T2> struct apply: std::tr1::is_base_of<T1, T2> {}; }; // returns whether Seq contains an element satisfying Pred template<typename Seq, typename Pred> struct contains_if : mpl::not_< boost::is_same< typename mpl::find_if< Seq, mpl::apply<Pred, mpl::_1> >::type, typename mpl::end<Seq>::type >
{}; Thanks for all help, Scott