#include <boost/proto/proto.hpp>

namespace proto = boost::proto;

struct start_type {};

struct element_grammar:
  proto::or_<
    proto::terminal<char[proto::N]>

    /* Replacing 1 with 0 makes the compilation error disappear.  */
#if 0
    ,
    proto::terminal<wchar_t[proto::N]>
#endif
  >
{};

struct grammar:
  proto::or_<
    element_grammar,
    proto::terminal<start_type>,
    proto::divides<grammar, grammar>
  >
{};

template<class Expr>
struct expression;

struct domain: 
  proto::domain<proto::generator<expression>, grammar> 
{};

template<class Expr>
struct expression: 
  proto::extends<Expr, expression<Expr>, domain>
{
  typedef expression<Expr> this_type;

  typedef
    proto::extends<Expr, this_type, domain>
  base_type;

  expression(const Expr &expr = Expr()): 
    base_type(expr)
  {}

};

expression<proto::terminal<start_type>::type> start;

int main(int argc, char** argv) {
  auto expr = start / "123";
}