parser_context.hpp

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/*=============================================================================
    Copyright (c) 2002-2003 Joel de Guzman
    Copyright (c) 2002-2003 Hartmut Kaiser
    http://spirit.sourceforge.net/

  Distributed under the Boost Software License, Version 1.0. (See accompanying
  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
=============================================================================*/
#if !defined(BOOST_SPIRIT_PARSER_CONTEXT_HPP)
#define BOOST_SPIRIT_PARSER_CONTEXT_HPP

///////////////////////////////////////////////////////////////////////////////
namespace boost
{
    namespace spirit
    {
    BOOST_SPIRIT_CLASSIC_NAMESPACE_BEGIN


    ///////////////////////////////////////////////////////////////////////////
    //
    //  default_parser_context_base class { default context base }
    //
    ///////////////////////////////////////////////////////////////////////////
    struct default_parser_context_base
    {
        template <typename DerivedT>
        struct aux {};
    };

    ///////////////////////////////////////////////////////////////////////////
    //
    //  parser_context_base class { base class of all context classes }
    //
    ///////////////////////////////////////////////////////////////////////////
    struct parser_context_base {};

    ///////////////////////////////////////////////////////////////////////////
    //
    //  parser_context class { default context }
    //
    ///////////////////////////////////////////////////////////////////////////
    struct nil_t;
    template<typename ContextT> struct parser_context_linker;

    template<typename AttrT = nil_t>
    struct parser_context : parser_context_base
    {
        typedef AttrT attr_t;
        typedef default_parser_context_base base_t;
        typedef parser_context_linker<parser_context<AttrT> > context_linker_t;

        template <typename ParserT>
        parser_context(ParserT const&) {}

        template <typename ParserT, typename ScannerT>
        void
        pre_parse(ParserT const&, ScannerT const&) {}

        template <typename ResultT, typename ParserT, typename ScannerT>
        ResultT&
        post_parse(ResultT& hit, ParserT const&, ScannerT const&)
        { return hit; }
    };

    ///////////////////////////////////////////////////////////////////////////
    //
    //  context_aux class
    //
    //      context_aux<ContextT, DerivedT> is a class derived from the
    //      ContextT's nested base_t::base<DerivedT> template class. (see
    //      default_parser_context_base::aux for an example).
    //
    //      Basically, this class provides ContextT dependent optional
    //      functionality to the derived class DerivedT through the CRTP
    //      idiom (Curiously recurring template pattern).
    //
    ///////////////////////////////////////////////////////////////////////////
    template <typename ContextT, typename DerivedT>
    struct context_aux : public ContextT::base_t::template aux<DerivedT> {};

    ///////////////////////////////////////////////////////////////////////////
    //
    //  parser_scanner_linker and parser_scanner_linker classes
    //  { helper templates for the rule extensibility }
    //
    //      This classes can be 'overloaded' (defined elsewhere), to plug
    //      in additional functionality into the non-terminal parsing process.
    //
    ///////////////////////////////////////////////////////////////////////////
    #if !defined(BOOST_SPIRIT_PARSER_SCANNER_LINKER_DEFINED)
    #define BOOST_SPIRIT_PARSER_SCANNER_LINKER_DEFINED

    template<typename ScannerT>
    struct parser_scanner_linker : public ScannerT
    {
        parser_scanner_linker(ScannerT const scan_) : ScannerT(scan_) {}
    };

    #endif // !defined(BOOST_SPIRIT_PARSER_SCANNER_LINKER_DEFINED)

    //////////////////////////////////
    #if !defined(BOOST_SPIRIT_PARSER_CONTEXT_LINKER_DEFINED)
    #define BOOST_SPIRIT_PARSER_CONTEXT_LINKER_DEFINED

    template<typename ContextT>
    struct parser_context_linker : public ContextT
    {
        template <typename ParserT>
        parser_context_linker(ParserT const& p)
        : ContextT(p) {}

        template <typename ParserT, typename ScannerT>
        void pre_parse(ParserT const& p, ScannerT const& scan)
        { ContextT::pre_parse(p, scan); }

        template <typename ResultT, typename ParserT, typename ScannerT>
        ResultT&
        post_parse(ResultT& hit, ParserT const& p, ScannerT const& scan)
        { return ContextT::post_parse(hit, p, scan); }
    };

    #endif // !defined(BOOST_SPIRIT_PARSER_CONTEXT_LINKER_DEFINED)

    ///////////////////////////////////////////////////////////////////////////
    //
    //  BOOST_SPIRIT_CONTEXT_PARSE helper macro
    //
    //      The original implementation uses a template class. However, we
    //      need to lessen the template instantiation depth to help inferior
    //      compilers that sometimes choke on deep template instantiations.
    //      The objective is to avoid code redundancy. A macro, in this case
    //      is an obvious solution. Sigh!
    //
    //      WARNING: INTERNAL USE ONLY. NOT FOR PUBLIC CONSUMPTION.
    //
    ///////////////////////////////////////////////////////////////////////////
    #define BOOST_SPIRIT_CONTEXT_PARSE(scan, this_, scanner_t, context_t, result_t) \
            scanner_t scan_wrap(scan);                                              \
            context_t context_wrap(this_);                                          \
            context_wrap.pre_parse(this_, scan_wrap);                               \
            result_t hit = parse_main(scan);                                        \
            return context_wrap.post_parse(hit, this_, scan_wrap);

    BOOST_SPIRIT_CLASSIC_NAMESPACE_END

    } // namespace spirit
} // namespace boost

#endif