Hi, I am trying to make a template for building sequences of random numbers using Boost.Mpl, but apparently I haven't quite got the hang of it yet ;). Below is my code (adapted from the Boost.Random docs) and the compiler output (GCC v 3.4.2), I seem to have misunderstood the usage of mpl::first and mpl::second in lambdas or something. Can someone clarify what I've done wrong? The whole construct should be invoked with something like typedef utils::make_random_sequence<vector0_c<unsigned long>, utils::minstd_rand, 10>::type random_vector; to generator a vector_c of 10 random numbers. Thanks, Mark #include <cstdlib> #include <boost/static_assert.hpp> #include <boost/mpl/integral_c.hpp> #include <boost/mpl/plus.hpp> #include <boost/mpl/times.hpp> #include <boost/mpl/modulus.hpp> #include <boost/mpl/iter_fold.hpp> #include <boost/mpl/range_c.hpp> #include <boost/mpl/pair.hpp> #include <boost/mpl/erase.hpp> #include <boost/mpl/begin.hpp> #include <boost/mpl/end.hpp> #include <boost/mpl/push_back.hpp> #include <boost/mpl/lambda.hpp> #include <boost/type_traits/is_integral.hpp> namespace utils { using namespace boost::mpl; template<class T, class Formula, T seed> struct random : integral_c< T, template Formula::apply<seed>::value > { typedef random<T, Formula, value> next; template<T new_seed> struct reseed { typedef random<T, Formula, new_seed> type; }; }; template<class IntType, IntType a, IntType c, IntType m> struct linear_congruential { BOOST_STATIC_ASSERT(boost::is_integral<IntType>::value); typedef IntType value_type; template<IntType seed> struct apply : integral_c<IntType, (a * seed + c) % m> { }; }; typedef random< long, linear_congruential<long, 16807L, 0, 2147483647L>, 1043618065L > minstd_rand0; typedef random< long, linear_congruential<long, 48271L, 0, 2147483647L>, 399268537L > minstd_rand; template<class integral_sequence, class generator, size_t size> struct make_random_sequence { typedef typename iter_fold< range_c<size_t, 1, size>, pair< typename erase< integral_sequence, begin<integral_sequence>, end<integral_sequence> >::type, generator >, pair< push_back< first<_1>, second<_1> >::type, second<_1>::next > >::type type; }; } 28: error: missing `>' to terminate the template argument list 28: error: template argument 2 is invalid 28: error: expected `{' before "template" 28: error: expected unqualified-id before "template" 28: error: expected `;' before "template" C:/Boost/include/boost-1_33/boost/mpl/pair.hpp: In instantiation of `boost::mpl::first<mpl_::_1>': C:/Boost/include/boost-1_33/boost/mpl/aux_/has_tag.hpp:20: instantiated from `boost::mpl::aux::has_tag<boost::mpl::first<mpl_::_1>, mpl_::bool_< false> >' C:/Boost/include/boost-1_33/boost/mpl/sequence_tag.hpp:115: instantiated from `boost::mpl::sequence_tag<boost::mpl::first<mpl_::_1> >' C:/Boost/include/boost-1_33/boost/mpl/push_back.hpp:32: instantiated from `boost::mpl::push_back<boost::mpl::first<mpl_::_1>, boost::mpl::second<mpl_::_1> >' 85: instantiated from here C:/Boost/include/boost-1_33/boost/mpl/pair.hpp:43: error: no type named `first' in `struct mpl_::_1' 85: error: `type' is not a member of `boost::mpl::push_back<boost::mpl::first<mpl_::_1>, boost::mpl::second<mpl_::_1> >' 85: error: `type' is not a member of `boost::mpl::push_back<boost::mpl::first<mpl_::_1>, boost::mpl::second<mpl_::_1> >' C:/Boost/include/boost-1_33/boost/mpl/pair.hpp: In instantiation of `boost::mpl::second<mpl_::_1>': 86: instantiated from here C:/Boost/include/boost-1_33/boost/mpl/pair.hpp:56: error: no type named `second' in `struct mpl_::_1' 86: error: `next' is not a member of `boost::mpl::second<mpl_::_1>' 86: error: `next' is not a member of `boost::mpl::second<mpl_::_1>' 88: error: template argument 1 is invalid 88: error: template argument 2 is invalid 88: error: template argument 3 is invalid 88: error: `type' does not name a type