Okay, just image some sort of code like this: typedef mpl::vector_c v; typedef mpl::accumulate,MPL_METAFUNC(_1*CONS(10)+_2)>::type::value result_value; // =123 Imaginably, the implementation of MPL_METAFUNC would involve BOOST_TYPEOF to deduce the type of "_1*CONS(10)+_2" so as to construct a corresponding metafunction, that is, "mpl::plus<_2,mpl::times<_1,int_<10> > >" (CONS here is used to work around the embarrassment that 10 becomes sort of variable when passed directly to operator*, so we use CONS(10) which expands into something like "int_<10>()" which entirely preserve "10" at compile-time). Arguably this is feasible, but I lack the time to implement it fully. (although it would be pretty simple, e.g. #define DEFINE_BINARY_OP(op,mpl_binray_op) \ template \ mpl_binary_op operator op (T t, U u) \ { \ return mpl_binary_op(); \ } \ DEFINE_OP(+,mpl::plus) DEFINE_OP(-,mpl::minus) DEFINE_OP(*,mpl::times) DEFINE_OP(/,mpl::divide) ... Admittedly, there exists a name confliction between mpl::_1 and lambda::_1 due to the inherent difference between type and variable in the language, so we couldn't use the same _1 and _2 in both "plus<_1,_2>" and "_1+_2". Any good remedies for that?(of course we could always turn to "_1()+_2()" in which _1/2 means mpl::_1/2) My question is: Is this valuable?(IMO,it'll make arithmetic operation in metaprogramming much easier and clearer, just watch "_1*10+_2" v.s. "mpl::plus<_2,mpl::times<_1,int_<10> > >" you'll see that). And if it is, would Dave consider adding it to MPL? Thanks in advance! -- Regards!