The following compiles (VC7.1, gcc3.2), and I am wondering if this is the intended behaviour(boost 1.32) Note the two default parameters to eval_if. here #include <iostream> #include <boost/mpl/eval_if.hpp> int main() { typedef boost::mpl::eval_if< boost::mpl::true_ // whatever nullary metafunction >::type type; std::cout << type::value <<'\n'; // outputs 0 } regards Andy Little