boost/spirit/home/phoenix/scope/let.hpp

   1 /*=============================================================================
   2     Copyright (c) 2001-2007 Joel de Guzman
   3     Copyright (c) 2004 Daniel Wallin
   4
   5     Distributed under the Boost Software License, Version 1.0. (See accompanying
   6     file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   7 ==============================================================================*/
   8 #ifndef PHOENIX_SCOPE_LET_HPP
   9 #define PHOENIX_SCOPE_LET_HPP
  10
  11 #include <boost/spirit/home/phoenix/core/limits.hpp>
  12 #include <boost/spirit/home/phoenix/core/composite.hpp>
  13 #include <boost/spirit/home/phoenix/scope/scoped_environment.hpp>
  14 #include <boost/spirit/home/phoenix/scope/detail/local_variable.hpp>
  15 #include <boost/spirit/home/phoenix/detail/local_reference.hpp>
  16 #include <boost/spirit/home/phoenix/core/actor.hpp>
  17 #include <boost/fusion/include/transform.hpp>
  18 #include <boost/fusion/include/as_vector.hpp>
  19 #include <boost/mpl/eval_if.hpp>
  20 #include <boost/mpl/bool.hpp>
  21
  22 namespace boost { namespace phoenix
  23 {
  24     template <typename Base, typename Vars, typename Map>
  25     struct let_actor : Base
  26     {
  27         typedef typename
  28             mpl::fold<
  29                 Vars
  30               , mpl::false_
  31               , detail::compute_no_nullary
  32             >::type
  33         no_nullary;
  34
  35         template <typename Env>
  36         struct result
  37         {
  38             typedef typename
  39                 fusion::result_of::as_vector<
  40                     typename fusion::result_of::transform<
  41                         Vars
  42                       , detail::initialize_local<Env>
  43                     >::type
  44                 >::type
  45             locals_type;
  46
  47             typedef typename Base::template
  48                 result<scoped_environment<Env, Env, locals_type, Map> >::type
  49             result_type;
  50
  51             typedef typename
  52                 detail::unwrap_local_reference<result_type>::type
  53             type;
  54         };
  55
  56         let_actor(Base const& base, Vars const& vars)
  57             : Base(base), vars(vars) {}
  58
  59         template <typename Env>
  60         typename result<Env>::type
  61         eval(Env const& env) const
  62         {
  63             typedef typename
  64                 fusion::result_of::as_vector<
  65                     typename fusion::result_of::transform<
  66                         Vars
  67                       , detail::initialize_local<Env>
  68                     >::type
  69                 >::type
  70             locals_type;
  71
  72             locals_type locals =
  73                 fusion::as_vector(
  74                     fusion::transform(
  75                         vars
  76                       , detail::initialize_local<Env>(env)));
  77
  78             typedef typename result<Env>::type RT;
  79             return RT(Base::eval(
  80                 scoped_environment<Env, Env, locals_type, Map>(
  81                     env
  82                   , env
  83                   , locals)));
  84         }
  85
  86         Vars vars;
  87     };
  88
  89     template <typename Vars, typename Map>
  90     struct let_actor_gen
  91     {
  92         template <typename Base>
  93         actor<let_actor<Base, Vars, Map> > const
  94         operator[](actor<Base> const& base) const
  95         {
  96             return let_actor<Base, Vars, Map>(base, vars);
  97         }
  98
  99         let_actor_gen(Vars const& vars)
 100             : vars(vars) {}
 101
 102         Vars vars;
 103     };
 104
 105     template <typename Key>
 106     struct local_variable; // forward
 107     struct assign_eval; // forward
 108
 109     struct let_gen
 110     {
 111         template <typename K0, typename V0>
 112         let_actor_gen<
 113             fusion::vector<V0>
 114           , detail::map_local_index_to_tuple<K0>
 115         >
 116         operator()(
 117             actor<composite<assign_eval, fusion::vector<local_variable<K0>, V0> > > const& a0
 118         ) const
 119         {
 120             return fusion::vector<V0>(fusion::at_c<1>(a0));
 121         }
 122
 123         template <typename K0, typename K1, typename V0, typename V1>
 124         let_actor_gen<
 125             fusion::vector<V0, V1>
 126           , detail::map_local_index_to_tuple<K0, K1>
 127         >
 128         operator()(
 129             actor<composite<assign_eval, fusion::vector<local_variable<K0>, V0> > > const& a0
 130           , actor<composite<assign_eval, fusion::vector<local_variable<K1>, V1> > > const& a1
 131         ) const
 132         {
 133             return fusion::vector<V0, V1>(fusion::at_c<1>(a0), fusion::at_c<1>(a1));
 134         }
 135
 136         // Bring in the rest...
 137         #define PHOENIX_LOCAL_GEN_NAME let_actor_gen
 138         #include <boost/spirit/home/phoenix/scope/detail/local_gen.hpp>
 139         #undef PHOENIX_LOCAL_GEN_NAME
 140     };
 141
 142     let_gen const let = let_gen();
 143 }}
 144
 145 #endif