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   1 ///////////////////////////////////////////////////////////////////////////////
   2 // as_alternate.hpp
   3 //
   4 //  Copyright 2008 Eric Niebler. Distributed under the Boost
   5 //  Software License, Version 1.0. (See accompanying file
   6 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7
   8 #ifndef BOOST_XPRESSIVE_DETAIL_STATIC_TRANSFORMS_AS_ALTERNATE_HPP_EAN_04_01_2007
   9 #define BOOST_XPRESSIVE_DETAIL_STATIC_TRANSFORMS_AS_ALTERNATE_HPP_EAN_04_01_2007
  10
  11 // MS compatible compilers support #pragma once
  12 #if defined(_MSC_VER) && (_MSC_VER >= 1020)
  13 # pragma once
  14 #endif
  15
  16 #include <boost/config.hpp>
  17 #include <boost/mpl/assert.hpp>
  18 #include <boost/type_traits/is_same.hpp>
  19 #include <boost/proto/core.hpp>
  20 #include <boost/xpressive/detail/detail_fwd.hpp>
  21 #include <boost/xpressive/detail/static/static.hpp>
  22 #include <boost/xpressive/detail/core/matcher/alternate_matcher.hpp>
  23 #include <boost/xpressive/detail/utility/cons.hpp>
  24
  25 namespace boost { namespace xpressive
  26 {
  27     namespace detail
  28     {
  29         ///////////////////////////////////////////////////////////////////////////////
  30         // alternates_list
  31         //   a fusion-compatible sequence of alternate expressions, that also keeps
  32         //   track of the list's width and purity.
  33         template<typename Head, typename Tail>
  34         struct alternates_list
  35           : fusion::cons<Head, Tail>
  36         {
  37             BOOST_STATIC_CONSTANT(std::size_t, width = Head::width == Tail::width ? Head::width : detail::unknown_width::value);
  38             BOOST_STATIC_CONSTANT(bool, pure = Head::pure && Tail::pure);
  39
  40             alternates_list(Head const &head, Tail const &tail)
  41               : fusion::cons<Head, Tail>(head, tail)
  42             {
  43             }
  44         };
  45
  46         template<typename Head>
  47         struct alternates_list<Head, fusion::nil>
  48           : fusion::cons<Head, fusion::nil>
  49         {
  50             BOOST_STATIC_CONSTANT(std::size_t, width = Head::width);
  51             BOOST_STATIC_CONSTANT(bool, pure = Head::pure);
  52
  53             alternates_list(Head const &head, fusion::nil const &tail)
  54               : fusion::cons<Head, fusion::nil>(head, tail)
  55             {
  56             }
  57         };
  58     }
  59
  60     namespace grammar_detail
  61     {
  62         ///////////////////////////////////////////////////////////////////////////////
  63         // in_alternate_list
  64         template<typename Grammar, typename Callable = proto::callable>
  65         struct in_alternate_list : proto::transform<in_alternate_list<Grammar, Callable> >
  66         {
  67             template<typename Expr, typename State, typename Data>
  68             struct impl : proto::transform_impl<Expr, State, Data>
  69             {
  70                 typedef
  71                     detail::alternates_list<
  72                         typename Grammar::template impl<
  73                             Expr
  74                           , detail::alternate_end_xpression
  75                           , Data
  76                         >::result_type
  77                       , State
  78                     >
  79                 result_type;
  80
  81                 result_type operator ()(
  82                     typename impl::expr_param expr
  83                   , typename impl::state_param state
  84                   , typename impl::data_param data
  85                 ) const
  86                 {
  87                     return result_type(
  88                         typename Grammar::template impl<Expr, detail::alternate_end_xpression, Data>()(
  89                             expr
  90                           , detail::alternate_end_xpression()
  91                           , data
  92                         )
  93                       , state
  94                     );
  95                 }
  96             };
  97         };
  98
  99         ///////////////////////////////////////////////////////////////////////////////
 100         // as_alternate_matcher
 101         template<typename Grammar, typename Callable = proto::callable>
 102         struct as_alternate_matcher : proto::transform<as_alternate_matcher<Grammar, Callable> >
 103         {
 104             template<typename Expr, typename State, typename Data>
 105             struct impl : proto::transform_impl<Expr, State, Data>
 106             {
 107                 typedef typename impl::data data_type;
 108                 typedef
 109                     detail::alternate_matcher<
 110                         typename Grammar::template impl<Expr, State, Data>::result_type
 111                       , typename data_type::traits_type
 112                     >
 113                 result_type;
 114
 115                 result_type operator ()(
 116                     typename impl::expr_param expr
 117                   , typename impl::state_param state
 118                   , typename impl::data_param data
 119                 ) const
 120                 {
 121                     return result_type(
 122                         typename Grammar::template impl<Expr, State, Data>()(expr, state, data)
 123                     );
 124                 }
 125             };
 126         };
 127     }
 128
 129 }}
 130
 131 #endif