1///////////////////////////////////////////////////////////////////////////////
2/// \file when.hpp
3/// Definition of when transform.
4//
5// Copyright 2008 Eric Niebler. Distributed under the Boost
6// Software License, Version 1.0. (See accompanying file
7// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
8
9#ifndef BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007
10#define BOOST_PROTO_TRANSFORM_WHEN_HPP_EAN_10_29_2007
11
12#include <boost/preprocessor/cat.hpp>
13#include <boost/preprocessor/repetition/enum_params.hpp>
14#include <boost/preprocessor/repetition/enum_trailing_params.hpp>
15#include <boost/preprocessor/iteration/iterate.hpp>
16#include <boost/mpl/at.hpp>
17#include <boost/mpl/if.hpp>
18#include <boost/mpl/map.hpp>
19#include <boost/mpl/eval_if.hpp>
20#include <boost/proto/proto_fwd.hpp>
21#include <boost/proto/traits.hpp>
22#include <boost/proto/transform/call.hpp>
23#include <boost/proto/transform/make.hpp>
24#include <boost/proto/transform/impl.hpp>
25#include <boost/proto/transform/env.hpp>
26
27#if defined(_MSC_VER)
28# pragma warning(push)
29# pragma warning(disable : 4714) // function 'xxx' marked as __forceinline not inlined
30#endif
31
32namespace boost { namespace proto
33{
34 namespace detail
35 {
36 template<typename Grammar, typename R, typename Fun>
37 struct when_impl
38 : transform<when<Grammar, Fun> >
39 {
40 typedef Grammar first;
41 typedef Fun second;
42 typedef typename Grammar::proto_grammar proto_grammar;
43
44 // Note: do not evaluate is_callable<R> in this scope.
45 // R may be an incomplete type at this point.
46
47 template<typename Expr, typename State, typename Data>
48 struct impl : transform_impl<Expr, State, Data>
49 {
50 // OK to evaluate is_callable<R> here. R should be compete by now.
51 typedef
52 typename mpl::if_c<
53 is_callable<R>::value
54 , proto::call<Fun> // "R" is a function to call
55 , proto::make<Fun> // "R" is an object to construct
56 >::type
57 which;
58
59 typedef typename which::template impl<Expr, State, Data>::result_type result_type;
60
61 /// Evaluate <tt>R(A0,A1,...)</tt> as a transform either with
62 /// <tt>call\<\></tt> or with <tt>make\<\></tt> depending on
63 /// whether <tt>is_callable\<R\>::value</tt> is \c true or
64 /// \c false.
65 ///
66 /// \param e The current expression
67 /// \param s The current state
68 /// \param d An arbitrary data
69 /// \pre <tt>matches\<Expr, Grammar\>::value</tt> is \c true
70 /// \return <tt>which()(e, s, d)</tt>
71 BOOST_FORCEINLINE
72 result_type operator ()(
73 typename impl::expr_param e
74 , typename impl::state_param s
75 , typename impl::data_param d
76 ) const
77 {
78 return typename which::template impl<Expr, State, Data>()(e, s, d);
79 }
80 };
81 };
82 }
83
84 /// \brief A grammar element and a PrimitiveTransform that associates
85 /// a transform with the grammar.
86 ///
87 /// Use <tt>when\<\></tt> to override a grammar's default transform
88 /// with a custom transform. It is for used when composing larger
89 /// transforms by associating smaller transforms with individual
90 /// rules in your grammar, as in the following transform which
91 /// counts the number of terminals in an expression.
92 ///
93 /// \code
94 /// // Count the terminals in an expression tree.
95 /// // Must be invoked with initial state == mpl::int_<0>().
96 /// struct CountLeaves
97 /// : or_<
98 /// when<terminal<_>, mpl::next<_state>()>
99 /// , otherwise<fold<_, _state, CountLeaves> >
100 /// >
101 /// {};
102 /// \endcode
103 ///
104 /// In <tt>when\<G, T\></tt>, when \c T is a class type it is a
105 /// PrimitiveTransform and the following equivalencies hold:
106 ///
107 /// <tt>boost::result_of\<when\<G,T\>(E,S,V)\>::type</tt> is the same as
108 /// <tt>boost::result_of\<T(E,S,V)\>::type</tt>.
109 ///
110 /// <tt>when\<G,T\>()(e,s,d)</tt> is the same as
111 /// <tt>T()(e,s,d)</tt>.
112 template<typename Grammar, typename PrimitiveTransform /*= Grammar*/>
113 struct when
114 : PrimitiveTransform
115 {
116 typedef Grammar first;
117 typedef PrimitiveTransform second;
118 typedef typename Grammar::proto_grammar proto_grammar;
119 };
120
121 /// \brief A specialization that treats function pointer Transforms as
122 /// if they were function type Transforms.
123 ///
124 /// This specialization requires that \c Fun is actually a function type.
125 ///
126 /// This specialization is required for nested transforms such as
127 /// <tt>when\<G, T0(T1(_))\></tt>. In C++, functions that are used as
128 /// parameters to other functions automatically decay to funtion
129 /// pointer types. In other words, the type <tt>T0(T1(_))</tt> is
130 /// indistinguishable from <tt>T0(T1(*)(_))</tt>. This specialization
131 /// is required to handle these nested function pointer type transforms
132 /// properly.
133 template<typename Grammar, typename Fun>
134 struct when<Grammar, Fun *>
135 : when<Grammar, Fun>
136 {};
137
138 /// \brief Syntactic sugar for <tt>when\<_, Fun\></tt>, for use
139 /// in grammars to handle all the cases not yet handled.
140 ///
141 /// Use <tt>otherwise\<T\></tt> in your grammars as a synonym for
142 /// <tt>when\<_, T\></tt> as in the following transform which
143 /// counts the number of terminals in an expression.
144 ///
145 /// \code
146 /// // Count the terminals in an expression tree.
147 /// // Must be invoked with initial state == mpl::int_<0>().
148 /// struct CountLeaves
149 /// : or_<
150 /// when<terminal<_>, mpl::next<_state>()>
151 /// , otherwise<fold<_, _state, CountLeaves> >
152 /// >
153 /// {};
154 /// \endcode
155 template<typename Fun>
156 struct otherwise
157 : when<_, Fun>
158 {};
159
160 namespace envns_
161 {
162 // Define the transforms global
163 BOOST_PROTO_DEFINE_ENV_VAR(transforms_type, transforms);
164 }
165
166 using envns_::transforms;
167
168 /// \brief This specialization uses the Data parameter as a collection
169 /// of transforms that can be indexed by the specified rule.
170 ///
171 /// Use <tt>when\<T, external_transform\></tt> in your code when you would like
172 /// to define a grammar once and use it to evaluate expressions with
173 /// many different sets of transforms. The transforms are found by
174 /// using the Data parameter as a map from rules to transforms.
175 ///
176 /// See \c action_map for an example.
177 template<typename Grammar>
178 struct when<Grammar, external_transform>
179 : proto::transform<when<Grammar, external_transform> >
180 {
181 typedef Grammar first;
182 typedef external_transform second;
183 typedef typename Grammar::proto_grammar proto_grammar;
184
185 template<typename Expr, typename State, typename Data>
186 struct impl
187 : remove_reference<
188 typename mpl::eval_if_c<
189 proto::result_of::has_env_var<Data, transforms_type>::value
190 , proto::result_of::env_var<Data, transforms_type>
191 , proto::result_of::env_var<Data, data_type>
192 >::type
193 >::type::template when<Grammar>::template impl<Expr, State, Data>
194 {};
195 };
196
197 /// \brief For defining a map of Rule/Transform pairs for use with
198 /// <tt>when\<T, external_transform\></tt> to make transforms external to the grammar
199 ///
200 /// The following code defines a grammar with a couple of external transforms.
201 /// It also defines an action_map that maps from rules to transforms. It then
202 /// passes that transforms map at the Data parameter to the grammar. In this way,
203 /// the behavior of the grammar can be modified post-hoc by passing a different
204 /// action_map.
205 ///
206 /// \code
207 /// struct int_terminal
208 /// : proto::terminal<int>
209 /// {};
210 ///
211 /// struct char_terminal
212 /// : proto::terminal<char>
213 /// {};
214 ///
215 /// struct my_grammar
216 /// : proto::or_<
217 /// proto::when< int_terminal, proto::external_transform >
218 /// , proto::when< char_terminal, proto::external_transform >
219 /// , proto::when<
220 /// proto::plus< my_grammar, my_grammar >
221 /// , proto::fold< _, int(), my_grammar >
222 /// >
223 /// >
224 /// {};
225 ///
226 /// struct my_transforms
227 /// : proto::external_transforms<
228 /// proto::when<int_terminal, print(proto::_value)>
229 /// , proto::when<char_terminal, print(proto::_value)>
230 /// >
231 /// {};
232 ///
233 /// proto::literal<int> i(1);
234 /// proto::literal<char> c('a');
235 /// my_transforms trx;
236 ///
237 /// // Evaluate "i+c" using my_grammar with the specified transforms:
238 /// my_grammar()(i + c, 0, trx);
239 /// \endcode
240 template<BOOST_PP_ENUM_PARAMS_WITH_A_DEFAULT(BOOST_MPL_LIMIT_MAP_SIZE, typename T, mpl::na)>
241 struct external_transforms
242 {
243 typedef mpl::map<BOOST_PP_ENUM_PARAMS(BOOST_MPL_LIMIT_MAP_SIZE, T)> map_type;
244
245 template<typename Rule>
246 struct when
247 : proto::when<_, typename mpl::at<map_type, Rule>::type>
248 {};
249 };
250
251 // Other specializations of proto::when are generated by the preprocessor...
252 #include <boost/proto/transform/detail/when.hpp>
253
254 /// INTERNAL ONLY
255 ///
256 template<typename Grammar, typename Transform>
257 struct is_callable<when<Grammar, Transform> >
258 : mpl::true_
259 {};
260
261}} // namespace boost::proto
262
263#if defined(_MSC_VER)
264# pragma warning(pop)
265#endif
266
267#endif
268