Yes. You want:
// Match any integral terminal proto::and_< proto::terminal< proto::_ >, proto::if_ < boost::is_integral< proto::_value >() >
That works a treat, thanks! Now I have another question about refining those terminals, when I have: struct big_number_grammar : proto::or_< proto::terminal<proto::_> , proto::plus< big_number_grammar, big_number_grammar > , proto::multiplies< big_number_grammar, big_number_grammar > , proto::minus< big_number_grammar, big_number_grammar > , proto::divides< big_number_grammar, big_number_grammar > , proto::unary_plus< big_number_grammar > , proto::negate< big_number_grammar > , proto::or_< proto::modulus<big_number_grammar, big_number_grammar> , proto::shift_left<big_number_grammar, integer_terminal> , proto::shift_right<big_number_grammar, integer_terminal> , proto::bitwise_and<big_number_grammar, big_number_grammar> > > {}; Then the operator overloads work just fine, but if I try and refine it to: struct big_number_grammar : proto::or_< proto::terminal<boost::math::big_number<proto::_> > , proto::plus< big_number_grammar, big_number_grammar > , proto::multiplies< big_number_grammar, big_number_grammar > , proto::minus< big_number_grammar, big_number_grammar > , proto::divides< big_number_grammar, big_number_grammar > , proto::unary_plus< big_number_grammar > , proto::negate< big_number_grammar > , proto::or_< proto::modulus<big_number_grammar, big_number_grammar> , proto::shift_left<big_number_grammar, integer_terminal> , proto::shift_right<big_number_grammar, integer_terminal> , proto::bitwise_and<big_number_grammar, big_number_grammar> > > {}; Then trying to add two big_number's results in: 1>m:\data\boost\sandbox\big_number\libs\math\ide\extended_real\scrap\scrap.cpp(24): error C2893: Failed to specialize function template 'const boost::proto::detail::enable_binary<boost::proto::domainns_::deduce_domain,boost::proto::detail::not_a_grammar,boost::mpl::or_<boost::proto::is_extension<T>,boost::proto::is_extension<Right>>,boost::proto::tag::plus,const Left,const Right>::type boost::proto::exprns_::operator +(const Left &,const Right &)' With the following template arguments: 'boost::math::mpf_real_50' 'boost::math::mpf_real_50' Where mpf_real_50 is just a typedef for "big_number<some_backend_type>". Is there anything obvious I'm doing wrong here? I'm using VC10 BTW, and big_number inherits from proto::terminal<big_number*> in case that makes any difference. Thanks again, John.