230 lines
7.6 KiB
C++
230 lines
7.6 KiB
C++
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/*=============================================================================
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Copyright (c) 2002-2003 Joel de Guzman
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Copyright (c) 2002 Juan Carlos Arevalo-Baeza
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Copyright (c) 2002-2003 Martin Wille
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http://spirit.sourceforge.net/
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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=============================================================================*/
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#ifndef BOOST_SPIRIT_IF_HPP
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#define BOOST_SPIRIT_IF_HPP
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#include <boost/spirit/home/classic/namespace.hpp>
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#include <boost/spirit/home/classic/core/parser.hpp>
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#include <boost/spirit/home/classic/core/composite/composite.hpp>
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#include <boost/spirit/home/classic/dynamic/impl/conditions.ipp>
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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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// if-else-parser, holds two alternative parsers and a conditional functor
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// that selects between them.
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template <typename ParsableTrueT, typename ParsableFalseT, typename CondT>
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struct if_else_parser
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: public condition_evaluator<typename as_parser<CondT>::type>
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, public binary
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<
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typename as_parser<ParsableTrueT>::type,
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typename as_parser<ParsableFalseT>::type,
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parser< if_else_parser<ParsableTrueT, ParsableFalseT, CondT> >
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>
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{
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typedef if_else_parser<ParsableTrueT, ParsableFalseT, CondT> self_t;
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typedef as_parser<ParsableTrueT> as_parser_true_t;
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typedef as_parser<ParsableFalseT> as_parser_false_t;
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typedef typename as_parser_true_t::type parser_true_t;
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typedef typename as_parser_false_t::type parser_false_t;
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typedef as_parser<CondT> cond_as_parser_t;
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typedef typename cond_as_parser_t::type condition_t;
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typedef binary<parser_true_t, parser_false_t, parser<self_t> > base_t;
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typedef condition_evaluator<condition_t> eval_t;
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if_else_parser
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(
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ParsableTrueT const& p_true,
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ParsableFalseT const& p_false,
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CondT const& cond_
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)
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: eval_t(cond_as_parser_t::convert(cond_))
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, base_t
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(
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as_parser_true_t::convert(p_true),
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as_parser_false_t::convert(p_false)
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)
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{ }
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template <typename ScannerT>
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struct result
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{
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typedef typename match_result<ScannerT, nil_t>::type type;
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};
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template <typename ScannerT>
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typename parser_result<self_t, ScannerT>::type
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parse(ScannerT const& scan) const
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{
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typedef typename parser_result
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<parser_true_t, ScannerT>::type then_result_t;
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typedef typename parser_result
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<parser_false_t, ScannerT>::type else_result_t;
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typename ScannerT::iterator_t const save(scan.first);
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std::ptrdiff_t length = this->evaluate(scan);
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if (length >= 0)
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{
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then_result_t then_result(this->left().parse(scan));
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if (then_result)
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{
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length += then_result.length();
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return scan.create_match(std::size_t(length), nil_t(), save, scan.first);
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}
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}
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else
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{
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else_result_t else_result(this->right().parse(scan));
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if (else_result)
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{
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length = else_result.length();
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return scan.create_match(std::size_t(length), nil_t(), save, scan.first);
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}
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}
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return scan.no_match();
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}
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};
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//////////////////////////////////
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// if-else-parser generator, takes the false-parser in brackets
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// and returns the if-else-parser.
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template <typename ParsableTrueT, typename CondT>
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struct if_else_parser_gen
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{
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if_else_parser_gen(ParsableTrueT const& p_true_, CondT const& cond_)
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: p_true(p_true_)
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, cond(cond_) {}
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template <typename ParsableFalseT>
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if_else_parser
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<
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ParsableTrueT,
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ParsableFalseT,
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CondT
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>
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operator[](ParsableFalseT const& p_false) const
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{
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return if_else_parser<ParsableTrueT, ParsableFalseT, CondT>
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(
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p_true,
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p_false,
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cond
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);
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}
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ParsableTrueT const &p_true;
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CondT const &cond;
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};
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//////////////////////////////////
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// if-parser, conditionally runs a parser is a functor condition is true.
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// If the condition is false, it fails the parse.
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// It can optionally become an if-else-parser through the member else_p.
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template <typename ParsableT, typename CondT>
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struct if_parser
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: public condition_evaluator<typename as_parser<CondT>::type>
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, public unary
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<
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typename as_parser<ParsableT>::type,
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parser<if_parser<ParsableT, CondT> > >
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{
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typedef if_parser<ParsableT, CondT> self_t;
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typedef as_parser<ParsableT> as_parser_t;
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typedef typename as_parser_t::type parser_t;
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typedef as_parser<CondT> cond_as_parser_t;
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typedef typename cond_as_parser_t::type condition_t;
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typedef condition_evaluator<condition_t> eval_t;
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typedef unary<parser_t, parser<self_t> > base_t;
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if_parser(ParsableT const& p, CondT const& cond_)
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: eval_t(cond_as_parser_t::convert(cond_))
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, base_t(as_parser_t::convert(p))
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, else_p(p, cond_)
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{}
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template <typename ScannerT>
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struct result
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{
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typedef typename match_result<ScannerT, nil_t>::type type;
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};
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template <typename ScannerT>
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typename parser_result<self_t, ScannerT>::type
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parse(ScannerT const& scan) const
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{
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typedef typename parser_result<parser_t, ScannerT>::type t_result_t;
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typename ScannerT::iterator_t const save(scan.first);
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std::ptrdiff_t length = this->evaluate(scan);
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if (length >= 0)
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{
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t_result_t then_result(this->subject().parse(scan));
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if (then_result)
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{
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length += then_result.length();
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return scan.create_match(std::size_t(length), nil_t(), save, scan.first);
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}
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return scan.no_match();
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}
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return scan.empty_match();
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}
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if_else_parser_gen<ParsableT, CondT> else_p;
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};
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//////////////////////////////////
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// if-parser generator, takes the true-parser in brackets and returns the
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// if-parser.
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template <typename CondT>
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struct if_parser_gen
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{
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if_parser_gen(CondT const& cond_) : cond(cond_) {}
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template <typename ParsableT>
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if_parser
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<
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ParsableT,
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CondT
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>
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operator[](ParsableT const& subject) const
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{
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return if_parser<ParsableT, CondT>(subject, cond);
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}
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CondT const &cond;
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};
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} // namespace impl
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//////////////////////////////////
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// if_p function, returns "if" parser generator
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template <typename CondT>
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impl::if_parser_gen<CondT>
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if_p(CondT const& cond)
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{
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return impl::if_parser_gen<CondT>(cond);
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}
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BOOST_SPIRIT_CLASSIC_NAMESPACE_END
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}} // namespace BOOST_SPIRIT_CLASSIC_NS
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#endif // BOOST_SPIRIT_IF_HPP
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