1 | /*=============================================================================
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2 | Copyright (c) 1998-2003 Joel de Guzman
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3 | Copyright (c) 2001 Daniel Nuffer
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4 | Copyright (c) 2002 Hartmut Kaiser
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5 | http://spirit.sourceforge.net/
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6 |
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7 | Use, modification and distribution is subject to the Boost Software
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8 | License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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9 | http://www.boost.org/LICENSE_1_0.txt)
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10 | =============================================================================*/
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11 | #if !defined(BOOST_SPIRIT_OPTIONAL_HPP)
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12 | #define BOOST_SPIRIT_OPTIONAL_HPP
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13 |
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14 | #include <boost/spirit/core/parser.hpp>
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15 | #include <boost/spirit/core/primitives/primitives.hpp>
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16 | #include <boost/spirit/core/composite/composite.hpp>
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17 | #include <boost/spirit/meta/as_parser.hpp>
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18 |
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19 | namespace boost { namespace spirit {
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20 |
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21 | ///////////////////////////////////////////////////////////////////////////
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22 | //
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23 | // optional class
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24 | //
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25 | // Handles expressions of the form:
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26 | //
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27 | // !a
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28 | //
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29 | // where a is a parser. The expression returns a composite
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30 | // parser that matches its subject zero (0) or one (1) time.
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31 | //
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32 | ///////////////////////////////////////////////////////////////////////////
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33 | struct optional_parser_gen;
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34 |
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35 | template <typename S>
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36 | struct optional
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37 | : public unary<S, parser<optional<S> > >
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38 | {
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39 | typedef optional<S> self_t;
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40 | typedef unary_parser_category parser_category_t;
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41 | typedef optional_parser_gen parser_generator_t;
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42 | typedef unary<S, parser<self_t> > base_t;
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43 |
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44 | optional(S const& a)
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45 | : base_t(a) {}
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46 |
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47 | template <typename ScannerT>
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48 | typename parser_result<self_t, ScannerT>::type
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49 | parse(ScannerT const& scan) const
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50 | {
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51 | typedef typename parser_result<self_t, ScannerT>::type result_t;
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52 | typedef typename ScannerT::iterator_t iterator_t;
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53 | iterator_t save = scan.first;
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54 | if (result_t r = this->subject().parse(scan))
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55 | {
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56 | return r;
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57 | }
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58 | else
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59 | {
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60 | scan.first = save;
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61 | return scan.empty_match();
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62 | }
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63 | }
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64 | };
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65 |
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66 | struct optional_parser_gen
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67 | {
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68 | template <typename S>
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69 | struct result
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70 | {
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71 | typedef optional<S> type;
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72 | };
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73 |
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74 | template <typename S>
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75 | static optional<S>
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76 | generate(parser<S> const& a)
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77 | {
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78 | return optional<S>(a.derived());
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79 | }
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80 | };
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81 |
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82 | template <typename S>
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83 | optional<S>
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84 | operator!(parser<S> const& a);
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85 |
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86 | }} // namespace boost::spirit
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87 |
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88 | #endif
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89 |
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90 | #include <boost/spirit/core/composite/impl/optional.ipp>
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