#include <string>
#include <iostream>
#include <boost/proto/proto.hpp>

namespace sql
{
   struct query_ {};
   typedef boost::proto::terminal<query_>::type QueryTerminal;
   QueryTerminal query = {};

   struct select_ {};
   typedef boost::proto::terminal<select_>::type SelectTerminal;
   SelectTerminal select = {};

   struct where_ {};
   typedef boost::proto::terminal<where_>::type WhereTerminal;
   WhereTerminal where = {};
    
   struct order_by_ {};
   typedef boost::proto::terminal<order_by_>::type OrderByTerminal;
   OrderByTerminal order_by = {};

   struct limit_ {};
   typedef boost::proto::terminal<limit_>::type LimitTerminal;
   LimitTerminal limit = {};

   struct OrderByGrammar;
   struct WhereGrammar;
   struct SelectGrammar;

   struct LimitGrammar:
      boost::proto::or_
      <
         boost::proto::shift_left<OrderByGrammar, LimitTerminal>,
         OrderByGrammar
      > {};


   struct OrderByGrammar:
      boost::proto::or_
      <
         boost::proto::shift_left<WhereGrammar, OrderByTerminal>,
         WhereGrammar
      > {};

   struct WhereGrammar:
      boost::proto::or_
      <
         boost::proto::shift_left<SelectGrammar, WhereTerminal>,
         SelectGrammar
      > {};

   struct SelectGrammar:
      boost::proto::or_
      <
         SelectTerminal
      > {};
}

template<class Expr>
void limit_eval(const Expr&)
{
   BOOST_MPL_ASSERT(( boost::proto::matches< Expr, sql::LimitGrammar > ));
}

template<class Expr>
void not_limit_eval(const Expr&)
{
   BOOST_MPL_ASSERT(( boost::mpl::not_<boost::proto::matches< Expr, sql::LimitGrammar > > ));
}

int main()
{
   limit_eval(sql::select << sql::order_by << sql::limit);
   limit_eval(sql::select << sql::order_by << sql::limit);
   limit_eval(sql::select << sql::where);
   limit_eval(sql::select << sql::order_by);
   limit_eval(sql::select << sql::limit);
   limit_eval(sql::select << sql::where << sql::limit);
   not_limit_eval(sql::select << sql::limit << sql::order_by);
}