metaparse/v1/look_ahead.hpp

0001 #ifndef BOOST_METAPARSE_V1_LOOK_AHEAD_HPP
0002 #define BOOST_METAPARSE_V1_LOOK_AHEAD_HPP
0003
0004 // Copyright Abel Sinkovics (abel@sinkovics.hu)   2011.
0005 // Distributed under the Boost Software License, Version 1.0.
0006 //    (See accompanying file LICENSE_1_0.txt or copy at
0007 //          http://www.boost.org/LICENSE_1_0.txt)
0008
0009 #include <boost/metaparse/v1/is_error.hpp>
0010 #include <boost/metaparse/v1/accept.hpp>
0011 #include <boost/metaparse/v1/get_result.hpp>
0012
0013 #include <boost/mpl/eval_if.hpp>
0014
0015 namespace boost
0016 {
0017   namespace metaparse
0018   {
0019     namespace v1
0020     {
0021       template <class P>
0022       struct look_ahead
0023       {
0024       private:
0025         template <class S, class Pos>
0026         struct no_error :
0027           accept<
0028             typename get_result<typename P::template apply<S, Pos> >::type,
0029             S,
0030             Pos
0031           >
0032         {};
0033       public:
0034         typedef look_ahead type;
0035
0036         template <class S, class Pos>
0037         struct apply :
0038           boost::mpl::eval_if<
0039             typename is_error<typename P::template apply<S, Pos> >::type,
0040             typename P::template apply<S, Pos>,
0041             no_error<S, Pos>
0042           >
0043         {};
0044       };
0045     }
0046   }
0047 }
0048
0049 #endif
0050