Hi, I'm trying to learn how to make my own lambda compatible function objects and I'm hoping that someone can nudge me in the right direction. My first try is called tuple_element. It takes an index as a template parameter and a tuple as an argument, returning the element at the given index: //should print "x" cout << tuple_element<1>(_1)(tuple<int,std::string>(2, "x")); I've got everything working except for the sig template. tuple_element looks like (mostly copied from lambda source code): template <int Index> struct tuple_element_action {}; template <int Index, typename Arg> inline const lambda_functor< lambda_functor_base< tuple_element_action<Index>, tuple<lambda_functor<Arg> > > > tuple_element(const lambda_functor<Arg>& a) { return lambda_functor_base< tuple_element_action<Index>, tuple<lambda_functor<Arg> > > ( tuple<lambda_functor<Arg> >(a)); } and the action: template<typename Args, int Index> class lambda_functor_base<tuple_element_action<Index>, Args> { public: Args args; template <class T> struct sig : tuples::element<Index,T> {}; explicit lambda_functor_base(const Args& a) : args(a) {} template<class RET, CALL_TEMPLATE_ARGS> RET call(CALL_FORMAL_ARGS) const { return detail::select(get<0>(args), CALL_ACTUAL_ARGS).get<Index>(); } }; When I try to compile my example in VC 7.1 I get an error that seems to indicate that the type being passed to the sig template is boost::tuples::null_type. Everything works if I hardwire it like: template <class T> struct sig { typedef std::string type; }; Any ideas? Thanks, Brock