rule_parser.hpp

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  template<class P> class parser_reference 
    : public parser< parser_reference<P> >
  {
    P const & ref_that;
  public:
    parser_reference(P & that)
    // we allow implicit conversion but forbid temporaries.
      : ref_that(that)
    { }

    typedef parser_reference<P>           self_t;
    typedef self_t const &                embed_t; 
    typedef typename P::parser_category_t parser_category_t;

    template<typename ScannerT> struct result 
    { typedef typename P::BOOST_NESTED_TEMPLATE result<ScannerT>::type type; };

    template<typename ScannerT> 
    typename result<ScannerT>::type
    parse(ScannerT const & scan) const
    { return this->ref_that.parse(scan); }
  };

  template<class P> parser_reference<P> 
  embed_by_reference(::BOOST_SPIRIT_CLASSIC_NS::parser<P> & p)
  { return p; }

BOOST_SPIRIT_CLASSIC_NAMESPACE_END

} } // namespace ::BOOST_SPIRIT_CLASSIC_NS

BOOST_TYPEOF_REGISTER_TEMPLATE(BOOST_SPIRIT_CLASSIC_NS::parser_reference, 1)

//------------------------------------------------------------------------------
// Expression templates for action placeholders.
//------------------------------------------------------------------------------

namespace boost { namespace spirit { 

BOOST_SPIRIT_CLASSIC_NAMESPACE_BEGIN

namespace type_of { 

  // No-operation functor

  struct nop_functor 
  {
    template<typename T>
    bool operator()(T const &) const 
    { return false; }
    template<typename T, typename U>
    bool operator()(T const &, U const &) const
    { return false; }

    typedef bool result_type;
  };

  // Composite action

  template<typename Action1, typename Action2>
  class composite_action
  {
    Action1 fnc_a1;
    Action2 fnc_a2;
  public:
    composite_action(Action1 const & a1, Action2 const & a2)
      : fnc_a1(a1), fnc_a2(a2)
    { }

    template<typename T>
    void operator()(T const & inp) const
    { fnc_a1(inp); fnc_a2(inp); }

    template<typename T, typename U>
    void operator()(T const & inp1, U const inp2) const
    { fnc_a1(inp1, inp2); fnc_a2(inp1, inp2); }
  };

  // Action concatenation (and optimize away nop_functorS)

  template<typename Action1, typename Action2>
  struct action_concatenator
  {
    typedef composite_action<Action1,Action2> type;

    static type concatenate(Action1 const & a1, Action2 const & a2)
    { return composite_action<Action1,Action2>(a1,a2); }
  };
  template<typename Action> struct action_concatenator<nop_functor, Action>
  {
    typedef Action type;

    static type concatenate(nop_functor const &, Action const & a) 
    { return a; }
  };
  template<typename Action> struct action_concatenator<Action, nop_functor>
  {
    typedef Action type;

    static type concatenate(Action const & a, nop_functor const &) 
    { return a; }
  };
  template<> struct action_concatenator<nop_functor, nop_functor>
  {
    typedef nop_functor type;

    static type concatenate(nop_functor const &, nop_functor const &) 
    { return nop_functor(); }
  };

  template<typename Action1, typename Action2>
  typename action_concatenator<Action1,Action2>::type 
  concatenate_actions(Action1 const & a1, Action2 const & a2)
  {
    return action_concatenator<Action1,Action2>::concatenate(a1,a2);
  }

  // Action chains

  enum action_chain_mode { replace, append };

  template<class Placeholder, action_chain_mode Mode, typename Action>
  class action_chain
  {
    Action fnc_action;
  public:
    action_chain(Action const & a)
      : fnc_action(a)
    { }

    typedef Action action_type;

    Action const & action() const { return fnc_action; }
  };

  // This operator adds actions to an action chain definition
  template<class PH, action_chain_mode M, typename A1, typename A2>
  action_chain<PH, M, typename action_concatenator<A1,A2>::type>
  operator, (action_chain<PH,M,A1> const & chain, A2 const & a)
  {
    return action_chain<PH,M,typename action_concatenator<A1,A2>::type>
        ( concatenate_actions(chain.action(), a) );
  }

  // Expression template for mutiple action chain assignments
  template<class ChainOrChains, class LastChain>
  class action_chains
  {
    ChainOrChains obj_head;
    LastChain     obj_tail;
  public:
    action_chains(ChainOrChains const & head, LastChain const & tail)
      : obj_head(head), obj_tail(tail)
    { }

    typedef ChainOrChains head_type;
    typedef LastChain     tail_type;

    head_type const & head() const { return obj_head; }
    tail_type const & tail() const { return obj_tail; }
  }; 

  // Action chain concatenation
  template<class Head, class Tail>
  action_chains<Head,Tail> make_chain(Head const & h, Tail const & t)
  { return action_chains<Head,Tail>(h,t); }

  template<class PH1, action_chain_mode M1, typename A1,  
           class PH2, action_chain_mode M2, typename A2>
  action_chains< action_chain<PH1,M1,A1>, action_chain<PH2,M2,A2> >
  operator, (action_chain<PH1,M1,A1> const & h, 
             action_chain<PH2,M2,A2> const & t)
  { return make_chain(h,t); }

  template<class Head, class Tail,class PH, action_chain_mode M, typename A>
  action_chains< action_chains<Head,Tail>, action_chain<PH,M,A> >
  operator, (action_chains<Head,Tail> const & h, action_chain<PH,M,A> const & t)
  { return make_chain(h,t); }


  // Extract the (maybe composite) action associated with an action 
  // placeholders from the chains with a fold algorithm.
  template<class Placeholder, typename StartAction, class NewChainOrChains>
  struct placeholdee
  {
    typedef StartAction type; 

    static type get(StartAction const & a, NewChainOrChains const &)
    { return a; }
  };

  template<class Placeholder, // <-- non-deduced
           typename StartAction, class NewChainOrChains>
  typename placeholdee<Placeholder,StartAction,NewChainOrChains>::type
  get_placeholdee(StartAction const & a, NewChainOrChains const & c)
  { return placeholdee<Placeholder,StartAction,NewChainOrChains>::get(a,c); }

  template<class Placeholder, typename StartAction, class Head, class Tail> 
  struct placeholdee
            < Placeholder, StartAction, action_chains<Head,Tail> >
  {
    typedef typename placeholdee<Placeholder,
      typename placeholdee<Placeholder,StartAction,Head>::type, Tail >::type
    type;

    static type get(StartAction const & a, action_chains<Head,Tail> const & c)
    {
      return get_placeholdee<Placeholder>(
        get_placeholdee<Placeholder>(a,c.head()), c.tail() );
    }
  };

  template<class Placeholder, typename StartAction, typename A>
  struct placeholdee
            < Placeholder, StartAction, action_chain<Placeholder,replace,A> >
  {
    typedef A type;

    static type get(StartAction const &, 
                    action_chain<Placeholder,replace,A> const & c)
    { return c.action(); }
  };

  template<class Placeholder, typename StartAction, typename A>
  struct placeholdee
            < Placeholder, StartAction, action_chain<Placeholder,append,A> >
  {
    typedef typename action_concatenator<StartAction,A>::type type;

    static type get(StartAction const & a, 
                    action_chain<Placeholder,append,A> const & c)
    { return concatenate_actions(a,c.action()); }
  };

} 

BOOST_SPIRIT_CLASSIC_NAMESPACE_END

} } // namespace ::BOOST_SPIRIT_CLASSIC_NS::type_of

BOOST_TYPEOF_REGISTER_TYPE(BOOST_SPIRIT_CLASSIC_NS::type_of::nop_functor)
BOOST_TYPEOF_REGISTER_TEMPLATE(BOOST_SPIRIT_CLASSIC_NS::type_of::composite_action,2)

//------------------------------------------------------------------------------
// Misc.utilities
//------------------------------------------------------------------------------

namespace boost { namespace spirit { 

BOOST_SPIRIT_CLASSIC_NAMESPACE_BEGIN

namespace type_of {

  // Utility function to create a dependency to a template argument.

  template<typename T, typename X>
  X const & depend_on_type(X const & x) 
  { return x; }

  // Utility to allow use parenthesized type expressions with commas inside
  // as a type within macros. Thanks to Dave Abrahams for telling me this nice
  // trick.

  #define BOOST_SPIRIT_RP_TYPE(x) \
    ::BOOST_SPIRIT_CLASSIC_NS::type_of::remove_special_fptr \
      < ::BOOST_SPIRIT_CLASSIC_NS::type_of::special_result & (*) x >::type

  struct special_result;

  template<typename T> struct remove_special_fptr { };
  template<typename T> struct remove_special_fptr< special_result & (*)(T) >
  { typedef T type; };

} 

BOOST_SPIRIT_CLASSIC_NAMESPACE_END

} } // namespace ::BOOST_SPIRIT_CLASSIC_NS::type_of

//------------------------------------------------------------------------------
#endif 
//------------------------------------------------------------------------------