I am hoping someone can point me the in right direction regarding this code snippit failing to compile. My suspicion is that it is a header problem but any help would be appreciated. In short, I seem to be missing why the binary form of mpl::transform won't work with fusion::vector. (unary form works just fine). The code below just attempts to make a std::pair<> from the contents of two sequences (this is just an example to illustrate the transform problem). If the two sequences are mpl::vectors, everything is fine. If they are fusion::vectors then 'lots of errors'. I'm fairly new to both mpl and fusion so I am not ruling out the fact that I have done something stupid. Thanks in advance, Mike See code below. #include <boost/mpl/transform.hpp> #include <boost/mpl/vector.hpp> #include <boost/fusion/include/mpl.hpp> #include <boost/fusion/container/vector.hpp> #include <utility> using namespace boost; struct my_make_pair { template<typename T1, typename T2> struct apply { typedef std::pair<T1,T2> type; }; }; int main(int argc, char *argv[]) { #if 0 typedef mpl::vector<int,long> seq1; typedef mpl::vector<float,double> seq2; typedef mpl::vector<std::pair<int,float>,std::pair<long,double> > pairs; typedef mpl::transform<seq1,seq2,my_make_pair>::type result; BOOST_MPL_ASSERT(( equal<result,pairs> )); #endif typedef fusion::vector<int,long> seq1; typedef fusion::vector<float,double> seq2; typedef fusion::vector<std::pair<int,float>,std::pair<long,double> > pairs; typedef mpl::transform<seq1,seq2,my_make_pair>::type result; BOOST_MPL_ASSERT(( equal<result,pairs> )); return 0; }