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/xpressive/proto/proto.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 alternates_listboost::xpressive::detail::alternates_list40 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 alternates_listboost::xpressive::detail::alternates_list53 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> 65 struct in_alternate_list : proto::callable 66 { 67 template<typename Sig> struct result {}; 68 69 template<typename This, typename Expr, typename State, typename Visitor> 70 struct result<This(Expr, State, Visitor)> 71 { 72 typedef detail::alternates_list< 73 typename Grammar::template result<void(Expr, detail::alternate_end_xpression, Visitor)>::type 74 , State 75 > type; 76 }; 77 78 template<typename Expr, typename State, typename Visitor> 79 typename result<void(Expr, State, Visitor)>::type operator ()boost::xpressive::grammar_detail::in_alternate_list80 operator ()(Expr const &expr, State const &state, Visitor &visitor) const 81 { 82 return typename result<void(Expr, State, Visitor)>::type( 83 Grammar()(expr, detail::alternate_end_xpression(), visitor) 84 , state 85 ); 86 } 87 }; 88 89 /////////////////////////////////////////////////////////////////////////////// 90 // as_alternate_matcher 91 template<typename Grammar> 92 struct as_alternate_matcher : proto::callable 93 { 94 template<typename Sig> struct result {}; 95 96 template<typename This, typename Expr, typename State, typename Visitor> 97 struct result<This(Expr, State, Visitor)> 98 { 99 typedef detail::alternate_matcher< 100 typename Grammar::template result<void(Expr, State, Visitor)>::type 101 , typename Visitor::traits_type 102 > type; 103 }; 104 105 template<typename Expr, typename State, typename Visitor> 106 typename result<void(Expr, State, Visitor)>::type operator ()boost::xpressive::grammar_detail::as_alternate_matcher107 operator ()(Expr const &expr, State const &state, Visitor &visitor) const 108 { 109 return typename result<void(Expr, State, Visitor)>::type( 110 Grammar()(expr, state, visitor) 111 ); 112 } 113 }; 114 115 } 116 117 }} 118 119 #endif 120