1 /*=============================================================================
2     Copyright (c) 2001-2011 Joel de Guzman
3 
4     Distributed under the Boost Software License, Version 1.0. (See accompanying
5     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6 =============================================================================*/
7 #if !defined(SPIRIT_DIFFERENCE_FEBRUARY_11_2007_1250PM)
8 #define SPIRIT_DIFFERENCE_FEBRUARY_11_2007_1250PM
9 
10 #if defined(_MSC_VER)
11 #pragma once
12 #endif
13 
14 #include <boost/spirit/home/qi/domain.hpp>
15 #include <boost/spirit/home/qi/meta_compiler.hpp>
16 #include <boost/spirit/home/qi/parser.hpp>
17 #include <boost/spirit/home/qi/detail/attributes.hpp>
18 #include <boost/spirit/home/support/info.hpp>
19 #include <boost/spirit/home/support/has_semantic_action.hpp>
20 #include <boost/spirit/home/support/handles_container.hpp>
21 #include <boost/fusion/include/at.hpp>
22 
23 namespace boost { namespace spirit
24 {
25     ///////////////////////////////////////////////////////////////////////////
26     // Enablers
27     ///////////////////////////////////////////////////////////////////////////
28     template <>
29     struct use_operator<qi::domain, proto::tag::minus> // enables -
30       : mpl::true_ {};
31 }}
32 
33 namespace boost { namespace spirit { namespace qi
34 {
35     template <typename Left, typename Right>
36     struct difference : binary_parser<difference<Left, Right> >
37     {
38         typedef Left left_type;
39         typedef Right right_type;
40 
41         template <typename Context, typename Iterator>
42         struct attribute
43         {
44             typedef typename
45                 traits::attribute_of<left_type, Context, Iterator>::type
46             type;
47         };
48 
differenceboost::spirit::qi::difference49         difference(Left const& left_, Right const& right_)
50           : left(left_), right(right_) {}
51 
52         template <typename Iterator, typename Context
53           , typename Skipper, typename Attribute>
parseboost::spirit::qi::difference54         bool parse(Iterator& first, Iterator const& last
55           , Context& context, Skipper const& skipper
56           , Attribute& attr_) const
57         {
58             // Unlike classic Spirit, with this version of difference, the rule
59             // lit("policeman") - "police" will always fail to match.
60 
61             // Spirit2 does not count the matching chars while parsing and
62             // there is no reliable and fast way to check if the LHS matches
63             // more than the RHS.
64 
65             // Try RHS first
66             Iterator start = first;
67             if (right.parse(first, last, context, skipper, unused))
68             {
69                 // RHS succeeds, we fail.
70                 first = start;
71                 return false;
72             }
73             // RHS fails, now try LHS
74             return left.parse(first, last, context, skipper, attr_);
75         }
76 
77         template <typename Context>
whatboost::spirit::qi::difference78         info what(Context& context) const
79         {
80             return info("difference",
81                 std::make_pair(left.what(context), right.what(context)));
82         }
83 
84         Left left;
85         Right right;
86     };
87 
88     ///////////////////////////////////////////////////////////////////////////
89     // Parser generators: make_xxx function (objects)
90     ///////////////////////////////////////////////////////////////////////////
91     template <typename Elements, typename Modifiers>
92     struct make_composite<proto::tag::minus, Elements, Modifiers>
93       : make_binary_composite<Elements, difference>
94     {};
95 }}}
96 
97 namespace boost { namespace spirit { namespace traits
98 {
99     ///////////////////////////////////////////////////////////////////////////
100     template <typename Left, typename Right>
101     struct has_semantic_action<qi::difference<Left, Right> >
102       : binary_has_semantic_action<Left, Right> {};
103 
104     ///////////////////////////////////////////////////////////////////////////
105     template <typename Left, typename Right, typename Attribute
106       , typename Context, typename Iterator>
107     struct handles_container<qi::difference<Left, Right>, Attribute, Context
108       , Iterator>
109       : binary_handles_container<Left, Right, Attribute, Context, Iterator> {};
110 }}}
111 
112 #endif
113