#include <boost/proto/proto.hpp>

namespace mpl = boost::mpl;
namespace proto = boost::proto;

typedef proto::terminal<int> int_terminal;
typedef proto::terminal<double> double_terminal;

template <typename Expr>
struct actor1;

struct domain1;

struct grammar1
    : proto::or_<
        proto::plus<grammar1, grammar1>
      , int_terminal
      , proto::if_<proto::is_sub_domain_of<proto::domain_of<proto::_>, domain1>()>
    >
{};

struct domain1
    : proto::domain<
        proto::pod_generator<actor1>
      , grammar1
      , proto::default_domain
    >
{};

template <typename Expr>
struct actor1
{
    BOOST_PROTO_BASIC_EXTENDS(Expr, actor1<Expr>, domain1)
};

template <typename Expr>
struct actor2;

struct grammar2
    : proto::or_<
        proto::plus<grammar2, grammar2>
      , double_terminal
    >
{};

struct domain2
    : proto::domain<
        proto::pod_generator<actor2>
      , grammar2
      , domain1
    >
{};

template <typename Expr>
struct actor2
{
    BOOST_PROTO_BASIC_EXTENDS(Expr, actor2<Expr>, domain2)
};

actor1<int_terminal::type> t1 = {{0}};
actor2<double_terminal::type> t2 = {{0}};

int main()
{
  t1;
  t1 + t1;
  t2;
  t2 + t2;
  t1 + t2;
}