x3/auxiliary/guard.hpp

0001 /*=============================================================================
0002     Copyright (c) 2001-2014 Joel de Guzman
0003
0004     Distributed under the Boost Software License, Version 1.0. (See accompanying
0005     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0006 =============================================================================*/
0007 #if !defined(BOOST_SPIRIT_X3_GUARD_FERBRUARY_02_2013_0649PM)
0008 #define BOOST_SPIRIT_X3_GUARD_FERBRUARY_02_2013_0649PM
0009
0010 #include <boost/spirit/home/x3/support/context.hpp>
0011 #include <boost/spirit/home/x3/directive/expect.hpp>
0012
0013 namespace boost { namespace spirit { namespace x3
0014 {
0015     enum class error_handler_result
0016     {
0017         fail
0018       , retry
0019       , accept
0020       , rethrow
0021     };
0022
0023     template <typename Subject, typename Handler>
0024     struct guard : unary_parser<Subject, guard<Subject, Handler>>
0025     {
0026         typedef unary_parser<Subject, guard<Subject, Handler>> base_type;
0027         static bool const is_pass_through_unary = true;
0028
0029         constexpr guard(Subject const& subject, Handler handler)
0030           : base_type(subject), handler(handler) {}
0031
0032         template <typename Iterator, typename Context
0033           , typename RuleContext, typename Attribute>
0034         bool parse(Iterator& first, Iterator const& last
0035           , Context const& context, RuleContext& rcontext, Attribute& attr) const
0036         {
0037             for (;;)
0038             {
0039                 try
0040                 {
0041                     Iterator i = first;
0042                     bool r = this->subject.parse(i, last, context, rcontext, attr);
0043                     if (r)
0044                         first = i;
0045                     return r;
0046                 }
0047                 catch (expectation_failure<Iterator> const& x)
0048                 {
0049                     switch (handler(first, last, x, context))
0050                     {
0051                         case error_handler_result::fail:
0052                             return false;
0053                         case error_handler_result::retry:
0054                             continue;
0055                         case error_handler_result::accept:
0056                             return true;
0057                         case error_handler_result::rethrow:
0058                             throw;
0059                     }
0060                 }
0061             }
0062             return false;
0063         }
0064
0065         Handler handler;
0066     };
0067 }}}
0068
0069 #endif