Chris@16: /*=============================================================================
Chris@16:     Copyright (c) 2002-2003 Martin Wille
Chris@16:     http://spirit.sourceforge.net/
Chris@16: 
Chris@16:     Use, modification and distribution is subject to the Boost Software
Chris@16:     License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
Chris@16:     http://www.boost.org/LICENSE_1_0.txt)
Chris@16: =============================================================================*/
Chris@16: #ifndef BOOST_SPIRIT_CONDITIONS_IPP
Chris@16: #define BOOST_SPIRIT_CONDITIONS_IPP
Chris@16: 
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: #include <boost/spirit/home/classic/meta/parser_traits.hpp>
Chris@16: #include <boost/spirit/home/classic/core/composite/epsilon.hpp>
Chris@16: 
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: namespace boost { namespace spirit {
Chris@16: 
Chris@16: BOOST_SPIRIT_CLASSIC_NAMESPACE_BEGIN
Chris@16: 
Chris@16:     namespace impl {
Chris@16: 
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16: //
Chris@16: // condition evaluation
Chris@16: //
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16:     //////////////////////////////////
Chris@16:     // condition_parser_selector, decides which parser to use for a condition
Chris@16:     // If the template argument is a parser then that parser is used.
Chris@16:     // If the template argument is a functor then a condition parser using
Chris@16:     // the functor is chosen
Chris@16: 
Chris@16:     template <typename T> struct embed_t_accessor
Chris@16:     {
Chris@16:         typedef typename T::embed_t type;
Chris@16:     };
Chris@16: 
Chris@16:     template <typename ConditionT>
Chris@16:     struct condition_parser_selector
Chris@16:     {
Chris@16:         typedef
Chris@16:             typename mpl::if_<
Chris@16:                     is_parser<ConditionT>,
Chris@16:                     ConditionT,
Chris@16:                     condition_parser<ConditionT>
Chris@16:                 >::type
Chris@16:             type;
Chris@16: 
Chris@16:         typedef typename embed_t_accessor<type>::type embed_t;
Chris@16:     };
Chris@16: 
Chris@16:     //////////////////////////////////
Chris@16:     // condition_evaluator, uses a parser to check wether a condition is met
Chris@16:     // takes a parser or a functor that can be evaluated in boolean context
Chris@16:     // as template parameter.
Chris@16: 
Chris@16:     // JDG 4-15-03 refactored
Chris@16:     template <typename ConditionT>
Chris@16:     struct condition_evaluator
Chris@16:     {
Chris@16:         typedef condition_parser_selector<ConditionT>       selector_t;
Chris@16:         typedef typename selector_t::type                   selected_t;
Chris@16:         typedef typename selector_t::embed_t                cond_embed_t;
Chris@16: 
Chris@16:         typedef typename boost::call_traits<cond_embed_t>::param_type
Chris@16:             param_t;
Chris@16: 
Chris@16:         condition_evaluator(param_t s) : cond(s) {}
Chris@16: 
Chris@16:         /////////////////////////////
Chris@16:         // evaluate, checks wether condition is met
Chris@16:         // returns length of a match or a negative number for no-match
Chris@16:         template <typename ScannerT>
Chris@16:         std::ptrdiff_t
Chris@16:         evaluate(ScannerT const &scan) const
Chris@16:         {
Chris@16:             typedef typename ScannerT::iterator_t iterator_t;
Chris@16:             typedef typename parser_result<selected_t, ScannerT>::type cres_t;
Chris@16:             iterator_t save(scan.first);
Chris@16:             cres_t result = cond.parse(scan);
Chris@16:             if (!result)            // reset the position if evaluation
Chris@16:                 scan.first = save;  // fails.
Chris@16:             return result.length();
Chris@16:         }
Chris@16: 
Chris@16:         cond_embed_t cond;
Chris@16:     };
Chris@16: 
Chris@16: ///////////////////////////////////////////////////////////////////////////////
Chris@16:     } // namespace impl
Chris@16: 
Chris@16: BOOST_SPIRIT_CLASSIC_NAMESPACE_END
Chris@16: 
Chris@16: }} // namespace boost::spirit
Chris@16: 
Chris@16: #endif