| /*============================================================================= |
| 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> |