95 lines
2.9 KiB
Plaintext
95 lines
2.9 KiB
Plaintext
/*=============================================================================
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Copyright (c) 1998-2003 Joel de Guzman
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Copyright (c) 2001 Daniel Nuffer
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Copyright (c) 2002 Hartmut Kaiser
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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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#if !defined(BOOST_SPIRIT_OPTIONAL_HPP)
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#define BOOST_SPIRIT_OPTIONAL_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/primitives/primitives.hpp>
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#include <boost/spirit/home/classic/core/composite/composite.hpp>
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#include <boost/spirit/home/classic/meta/as_parser.hpp>
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namespace boost { namespace spirit {
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BOOST_SPIRIT_CLASSIC_NAMESPACE_BEGIN
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///////////////////////////////////////////////////////////////////////////
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//
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// optional class
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//
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// Handles expressions of the form:
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//
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// !a
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//
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// where a is a parser. The expression returns a composite
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// parser that matches its subject zero (0) or one (1) time.
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//
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///////////////////////////////////////////////////////////////////////////
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struct optional_parser_gen;
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template <typename S>
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struct optional
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: public unary<S, parser<optional<S> > >
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{
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typedef optional<S> self_t;
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typedef unary_parser_category parser_category_t;
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typedef optional_parser_gen parser_generator_t;
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typedef unary<S, parser<self_t> > base_t;
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optional(S const& a)
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: base_t(a) {}
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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<self_t, ScannerT>::type result_t;
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typedef typename ScannerT::iterator_t iterator_t;
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iterator_t save = scan.first;
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if (result_t r = this->subject().parse(scan))
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{
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return r;
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}
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else
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{
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scan.first = save;
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return scan.empty_match();
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}
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}
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};
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struct optional_parser_gen
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{
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template <typename S>
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struct result
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{
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typedef optional<S> type;
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};
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template <typename S>
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static optional<S>
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generate(parser<S> const& a)
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{
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return optional<S>(a.derived());
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}
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};
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template <typename S>
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optional<S>
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operator!(parser<S> const& a);
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BOOST_SPIRIT_CLASSIC_NAMESPACE_END
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}} // namespace BOOST_SPIRIT_CLASSIC_NS
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#endif
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#include <boost/spirit/home/classic/core/composite/impl/optional.ipp>
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