CPPTM Answers - Exercise 6-1

 #include <boost/static_assert.hpp>
 #include <boost/mpl/reverse_fold.hpp>
 #include <boost/mpl/plus.hpp>
 #include <boost/mpl/int.hpp>
 #include <boost/mpl/placeholders.hpp>
 #include <boost/mpl/iterator_tags.hpp>
 #include <boost/mpl/begin.hpp>
 #include <boost/mpl/end.hpp>
 #include <boost/mpl/deref.hpp>
 #include <boost/mpl/times.hpp>

 namespace mpl = boost::mpl;
 using namespace mpl::placeholders;

 struct binary_sequence_tag {};

 template<unsigned long Q, unsigned long R>
 struct binary_iterator
 {
     typedef mpl::forward_iterator_tag category;
     typedef binary_iterator type;
     typedef binary_iterator<Q / 10, Q % 10> next;
 };

 template<>
 struct binary_iterator<0, 0> 
 {
     typedef binary_iterator type;
 };

 template<unsigned long N>
 struct binary_sequence 
 {
     typedef binary_sequence_tag tag;
 };

 typedef mpl::int_<2> two;

 template<unsigned long N>
 struct binary 
     : mpl::reverse_fold<
           binary_sequence<N>, 
           mpl::int_<0>, 
           mpl::plus<mpl::times<_1, two>, _2>
       >::type
 {
 };

 namespace boost
 {
     namespace mpl
     {
         template<>
         struct begin_impl<binary_sequence_tag>
         {
             template<typename Seq>
             struct apply;

             template<unsigned long N>
             struct apply<binary_sequence<N> > 
                 : binary_iterator<N / 10, N % 10>
             {};
         };

         template<>
         struct end_impl<binary_sequence_tag>
         {
             template<typename Seq>
             struct apply : binary_iterator<0, 0> {};
         };

         template<unsigned long Q, unsigned long R>
         struct deref<binary_iterator<Q, R> > : mpl::int_<R> {};
     }
 }

 int main()
 {
     BOOST_STATIC_ASSERT((binary<0>::value == 0));
     BOOST_STATIC_ASSERT((binary<1>::value == 1));
     BOOST_STATIC_ASSERT((binary<10>::value == 2));
     BOOST_STATIC_ASSERT((binary<11>::value == 3));
     BOOST_STATIC_ASSERT((binary<100>::value == 4));
     BOOST_STATIC_ASSERT((binary<101>::value == 5));
     BOOST_STATIC_ASSERT((binary<110>::value == 6));
     BOOST_STATIC_ASSERT((binary<111>::value == 7));
     return 0;
 }