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