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