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24 | </div> | |
25 | <div class="section"> | |
26 | <div class="titlepage"><div><div><h3 class="title"> | |
27 | <a name="phoenix.inside.actor"></a><a class="link" href="actor.html" title="Actors in Detail">Actors in Detail</a> | |
28 | </h3></div></div></div> | |
29 | <h5> | |
30 | <a name="phoenix.inside.actor.h0"></a> | |
31 | <span><a name="phoenix.inside.actor.actor"></a></span><a class="link" href="actor.html#phoenix.inside.actor.actor">Actor</a> | |
32 | </h5> | |
33 | <p> | |
34 | The main concept is the <code class="computeroutput"><span class="identifier">Actor</span></code>. | |
35 | An <code class="computeroutput"><span class="identifier">Actor</span></code> is a model of the | |
36 | <a href="http://www.boost.org/doc/libs/release/libs/fusion/doc/html/fusion/functional/concepts/poly.html" target="_top">Polymorphic | |
37 | Function Object</a> concept (that can accept 0 to N arguments (where | |
38 | N is a predefined maximum). | |
39 | </p> | |
40 | <p> | |
41 | An <code class="computeroutput"><span class="identifier">Actor</span></code> contains a valid | |
42 | Phoenix Expression, a call to one of the function call operator overloads, | |
43 | starts the evaluation process. | |
44 | </p> | |
45 | <div class="note"><table border="0" summary="Note"> | |
46 | <tr> | |
47 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> | |
48 | <th align="left">Note</th> | |
49 | </tr> | |
50 | <tr><td align="left" valign="top"><p> | |
51 | You can set <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_LIMIT</span></code>, | |
52 | the predefined maximum arity an actor can take. By default, <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_LIMIT</span></code> is set to 10. | |
53 | </p></td></tr> | |
54 | </table></div> | |
55 | <p> | |
56 | The <code class="computeroutput"><span class="identifier">actor</span></code> template class | |
57 | models the <code class="computeroutput"><span class="identifier">Actor</span></code> concept: | |
58 | </p> | |
59 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">></span> | |
60 | <span class="keyword">struct</span> <span class="identifier">actor</span> | |
61 | <span class="special">{</span> | |
62 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Sig</span><span class="special">></span> | |
63 | <span class="keyword">struct</span> <span class="identifier">result</span><span class="special">;</span> | |
64 | ||
65 | <span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">>::</span><span class="identifier">type</span> | |
66 | <span class="keyword">operator</span><span class="special">()()</span> <span class="keyword">const</span><span class="special">;</span> | |
67 | ||
68 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">></span> | |
69 | <span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">T0</span> <span class="special">&>::</span><span class="identifier">type</span> | |
70 | <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">T0</span><span class="special">&</span> <span class="identifier">_0</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> | |
71 | ||
72 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">></span> | |
73 | <span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">T0</span> <span class="keyword">const</span> <span class="special">&>::</span><span class="identifier">type</span> | |
74 | <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">T0</span> <span class="keyword">const</span> <span class="special">&</span> <span class="identifier">_0</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> | |
75 | ||
76 | <span class="comment">//...</span> | |
77 | <span class="special">};</span> | |
78 | </pre> | |
79 | <div class="table"> | |
80 | <a name="phoenix.inside.actor.t0"></a><p class="title"><b>Table 1.9. Actor Concept Requirements</b></p> | |
81 | <div class="table-contents"><table class="table" summary="Actor Concept Requirements"> | |
82 | <colgroup> | |
83 | <col> | |
84 | <col> | |
85 | </colgroup> | |
86 | <thead><tr> | |
87 | <th> | |
88 | <p> | |
89 | Expression | |
90 | </p> | |
91 | </th> | |
92 | <th> | |
93 | <p> | |
94 | Semantics | |
95 | </p> | |
96 | </th> | |
97 | </tr></thead> | |
98 | <tbody> | |
99 | <tr> | |
100 | <td> | |
101 | <p> | |
102 | <code class="computeroutput"><span class="identifier">actor</span><span class="special">(</span><span class="identifier">arg0</span><span class="special">,</span> | |
103 | <span class="identifier">arg1</span><span class="special">,</span> | |
104 | <span class="special">...,</span> <span class="identifier">argN</span><span class="special">)</span></code> | |
105 | </p> | |
106 | </td> | |
107 | <td> | |
108 | <p> | |
109 | Function call operators to start the evaluation | |
110 | </p> | |
111 | </td> | |
112 | </tr> | |
113 | <tr> | |
114 | <td> | |
115 | <p> | |
116 | <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">result_of</span><span class="special"><</span><span class="identifier">Actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">>(</span><span class="identifier">Arg0</span><span class="special">,</span> | |
117 | <span class="identifier">Arg1</span><span class="special">,</span> | |
118 | <span class="special">...,</span> <span class="identifier">ArgN</span><span class="special">)>::</span><span class="identifier">type</span></code> | |
119 | </p> | |
120 | </td> | |
121 | <td> | |
122 | <p> | |
123 | Result of the evaluation | |
124 | </p> | |
125 | </td> | |
126 | </tr> | |
127 | <tr> | |
128 | <td> | |
129 | <p> | |
130 | <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> | |
131 | <span class="identifier">Arg0</span><span class="special">,</span> | |
132 | <span class="identifier">Arg1</span><span class="special">,</span> | |
133 | <span class="special">...,</span> <span class="identifier">ArgN</span><span class="special">>::</span><span class="identifier">type</span></code> | |
134 | </p> | |
135 | </td> | |
136 | <td> | |
137 | <p> | |
138 | Result of the evaluation | |
139 | </p> | |
140 | </td> | |
141 | </tr> | |
142 | </tbody> | |
143 | </table></div> | |
144 | </div> | |
145 | <br class="table-break"><h5> | |
146 | <a name="phoenix.inside.actor.h1"></a> | |
147 | <span><a name="phoenix.inside.actor.function_call_operators"></a></span><a class="link" href="actor.html#phoenix.inside.actor.function_call_operators">Function | |
148 | Call Operators</a> | |
149 | </h5> | |
150 | <p> | |
151 | There are 2*N function call operators for 0 to N arguments (N == <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_LIMIT</span></code>). The actor class accepts | |
152 | the arguments and forwards the arguments to the default evaluation action. | |
153 | </p> | |
154 | <p> | |
155 | Additionally, there exist function call operators accepting permutations | |
156 | of const and non-const references. These operators are created for all N | |
157 | <= <code class="computeroutput"><span class="identifier">BOOST_PHOENIX_PERFECT_FORWARD_LIMIT</span></code> | |
158 | (which defaults to 3). | |
159 | </p> | |
160 | <div class="note"><table border="0" summary="Note"> | |
161 | <tr> | |
162 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> | |
163 | <th align="left">Note</th> | |
164 | </tr> | |
165 | <tr><td align="left" valign="top"> | |
166 | <p> | |
167 | <span class="bold"><strong>Forwarding Function Problem</strong></span> | |
168 | </p> | |
169 | <p> | |
170 | There is a known issue with current C++ called the "<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_top">Forwarding | |
171 | Function Problem</a>". The problem is that given an arbitrary | |
172 | function <code class="computeroutput"><span class="identifier">F</span></code>, using current | |
173 | C++ language rules, one cannot create a forwarding function <code class="computeroutput"><span class="identifier">FF</span></code> that transparently assumes the arguments | |
174 | of <code class="computeroutput"><span class="identifier">F</span></code>. | |
175 | </p> | |
176 | </td></tr> | |
177 | </table></div> | |
178 | <h5> | |
179 | <a name="phoenix.inside.actor.h2"></a> | |
180 | <span><a name="phoenix.inside.actor.context"></a></span><a class="link" href="actor.html#phoenix.inside.actor.context">Context</a> | |
181 | </h5> | |
182 | <p> | |
183 | On an actor function call, before calling the evaluation function, the actor | |
184 | created a <span class="bold"><strong>context</strong></span>. This context consists | |
185 | of an <code class="computeroutput"><span class="identifier">Environment</span></code> and an | |
186 | <code class="computeroutput"><span class="identifier">Action</span></code> part. These contain | |
187 | all information necessary to evaluate the given expression. | |
188 | </p> | |
189 | <div class="table"> | |
190 | <a name="phoenix.inside.actor.t1"></a><p class="title"><b>Table 1.10. Context Concept Requirements</b></p> | |
191 | <div class="table-contents"><table class="table" summary="Context Concept Requirements"> | |
192 | <colgroup> | |
193 | <col> | |
194 | <col> | |
195 | </colgroup> | |
196 | <thead><tr> | |
197 | <th> | |
198 | <p> | |
199 | Expression | |
200 | </p> | |
201 | </th> | |
202 | <th> | |
203 | <p> | |
204 | Semantics | |
205 | </p> | |
206 | </th> | |
207 | </tr></thead> | |
208 | <tbody> | |
209 | <tr> | |
210 | <td> | |
211 | <p> | |
212 | <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">context</span><span class="special"><</span><span class="identifier">Env</span><span class="special">,</span> | |
213 | <span class="identifier">Actions</span><span class="special">>::</span><span class="identifier">type</span></code> | |
214 | </p> | |
215 | </td> | |
216 | <td> | |
217 | <p> | |
218 | Type of a Context | |
219 | </p> | |
220 | </td> | |
221 | </tr> | |
222 | <tr> | |
223 | <td> | |
224 | <p> | |
225 | <code class="computeroutput"><span class="identifier">context</span><span class="special">(</span><span class="identifier">e</span><span class="special">,</span> | |
226 | <span class="identifier">a</span><span class="special">)</span></code> | |
227 | </p> | |
228 | </td> | |
229 | <td> | |
230 | <p> | |
231 | A Context containing environment <code class="computeroutput"><span class="identifier">e</span></code> | |
232 | and actions <code class="computeroutput"><span class="identifier">a</span></code> | |
233 | </p> | |
234 | </td> | |
235 | </tr> | |
236 | <tr> | |
237 | <td> | |
238 | <p> | |
239 | <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">env</span><span class="special"><</span><span class="identifier">Context</span><span class="special">>::</span><span class="identifier">type</span></code> | |
240 | </p> | |
241 | </td> | |
242 | <td> | |
243 | <p> | |
244 | Type of the contained Environment | |
245 | </p> | |
246 | </td> | |
247 | </tr> | |
248 | <tr> | |
249 | <td> | |
250 | <p> | |
251 | <code class="computeroutput"><span class="identifier">env</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span></code> | |
252 | </p> | |
253 | </td> | |
254 | <td> | |
255 | <p> | |
256 | The environment | |
257 | </p> | |
258 | </td> | |
259 | </tr> | |
260 | <tr> | |
261 | <td> | |
262 | <p> | |
263 | <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actions</span><span class="special"><</span><span class="identifier">Context</span><span class="special">>::</span><span class="identifier">type</span></code> | |
264 | </p> | |
265 | </td> | |
266 | <td> | |
267 | <p> | |
268 | Type of the contained Actions | |
269 | </p> | |
270 | </td> | |
271 | </tr> | |
272 | <tr> | |
273 | <td> | |
274 | <p> | |
275 | <code class="computeroutput"><span class="identifier">actions</span><span class="special">(</span><span class="identifier">ctx</span><span class="special">)</span></code> | |
276 | </p> | |
277 | </td> | |
278 | <td> | |
279 | <p> | |
280 | The actions | |
281 | </p> | |
282 | </td> | |
283 | </tr> | |
284 | </tbody> | |
285 | </table></div> | |
286 | </div> | |
287 | <br class="table-break"><h5> | |
288 | <a name="phoenix.inside.actor.h3"></a> | |
289 | <span><a name="phoenix.inside.actor.environment"></a></span><a class="link" href="actor.html#phoenix.inside.actor.environment">Environment</a> | |
290 | </h5> | |
291 | <p> | |
292 | The Environment is a model of <a href="http://www.boost.org/doc/libs/release/libs/fusion/doc/html/fusion/sequence/concepts/random_access_sequence.html" target="_top">Random | |
293 | Access Sequence</a>. | |
294 | </p> | |
295 | <p> | |
296 | The arguments passed to the actor's function call operator are collected | |
297 | inside the Environment: | |
298 | </p> | |
299 | <p> | |
300 | <span class="inlinemediaobject"><img src="../../images/funnel_in.png"></span> | |
301 | </p> | |
302 | <p> | |
303 | Other parts of the library (e.g. the scope module) extends the <code class="computeroutput"><span class="identifier">Environment</span></code> concept to hold other information | |
304 | such as local variables, etc. | |
305 | </p> | |
306 | <h5> | |
307 | <a name="phoenix.inside.actor.h4"></a> | |
308 | <span><a name="phoenix.inside.actor.actions"></a></span><a class="link" href="actor.html#phoenix.inside.actor.actions">Actions</a> | |
309 | </h5> | |
310 | <p> | |
311 | Actions is the part of Phoenix which are responsible for giving the actual | |
312 | expressions a specific behaviour. During the traversal of the Phoenix Expression | |
313 | Tree these actions are called whenever a specified rule in the grammar matches. | |
314 | </p> | |
315 | <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">actions</span> | |
316 | <span class="special">{</span> | |
317 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Rule</span><span class="special">></span> | |
318 | <span class="keyword">struct</span> <span class="identifier">when</span><span class="special">;</span> | |
319 | <span class="special">};</span> | |
320 | </pre> | |
321 | <p> | |
322 | The nested <code class="computeroutput"><span class="identifier">when</span></code> template | |
323 | is required to be <a href="http://www.boost.org/doc/libs/release/doc/html/PrimitiveTransform.html" target="_top">Proto | |
324 | Primitive Transform</a>. No worries, you don't have to learn <a href="http://www.boost.org/doc/libs/release/libs/proto/index.html" target="_top">Boost.Proto</a> | |
325 | just yet! Phoenix provides some wrappers to let you define simple actions | |
326 | without the need to dive deep into proto. | |
327 | </p> | |
328 | <p> | |
329 | Phoenix ships with a predefined <code class="computeroutput"><span class="identifier">default_actions</span></code> | |
330 | class that evaluates the expressions with C++ semantics: | |
331 | </p> | |
332 | <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">default_actions</span> | |
333 | <span class="special">{</span> | |
334 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Rule</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Dummy</span> <span class="special">=</span> <span class="keyword">void</span><span class="special">></span> | |
335 | <span class="keyword">struct</span> <span class="identifier">when</span> | |
336 | <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">_default</span><span class="special"><</span><span class="identifier">meta_grammar</span><span class="special">></span> | |
337 | <span class="special">{};</span> | |
338 | <span class="special">};</span> | |
339 | </pre> | |
340 | <p> | |
341 | For more information on how to use the default_actions class and how to attach | |
342 | custom actions to the evaluation process, see <a class="link" href="actions.html" title="More on Actions">more | |
343 | on actions</a>. | |
344 | </p> | |
345 | <h5> | |
346 | <a name="phoenix.inside.actor.h5"></a> | |
347 | <span><a name="phoenix.inside.actor.evaluation"></a></span><a class="link" href="actor.html#phoenix.inside.actor.evaluation">Evaluation</a> | |
348 | </h5> | |
349 | <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">evaluator</span> | |
350 | <span class="special">{</span> | |
351 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Context</span><span class="special">></span> | |
352 | <span class="emphasis"><em>unspecified</em></span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">Expr</span> <span class="special">&,</span> <span class="identifier">Context</span> <span class="special">&);</span> | |
353 | <span class="special">};</span> | |
354 | ||
355 | <span class="identifier">evaluator</span> <span class="keyword">const</span> <span class="identifier">eval</span> <span class="special">=</span> <span class="special">{};</span> | |
356 | </pre> | |
357 | <p> | |
358 | The evaluation of a Phoenix expression is started by a call to the function | |
359 | call operator of <code class="computeroutput"><span class="identifier">evaluator</span></code>. | |
360 | </p> | |
361 | <p> | |
362 | The evaluator is called by the <code class="computeroutput"><span class="identifier">actor</span></code> | |
363 | function operator overloads after the context is built up. For reference, | |
364 | here is a typical <code class="computeroutput"><span class="identifier">actor</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code> | |
365 | that accepts two arguments: | |
366 | </p> | |
367 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T1</span><span class="special">></span> | |
368 | <span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">T0</span> <span class="special">&,</span> <span class="identifier">T1</span> <span class="special">&>::</span><span class="identifier">type</span> | |
369 | <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">T0</span> <span class="special">&</span><span class="identifier">t0</span><span class="special">,</span> <span class="identifier">T1</span> <span class="special">&</span><span class="identifier">t1</span><span class="special">)</span> <span class="keyword">const</span> | |
370 | <span class="special">{</span> | |
371 | <span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector2</span><span class="special"><</span><span class="identifier">T0</span> <span class="special">&,</span> <span class="identifier">T1</span> <span class="special">&></span> <span class="identifier">env</span><span class="special">(</span><span class="identifier">t0</span><span class="special">,</span> <span class="identifier">t1</span><span class="special">);</span> | |
372 | ||
373 | <span class="keyword">return</span> <span class="identifier">eval</span><span class="special">(*</span><span class="keyword">this</span><span class="special">,</span> <span class="identifier">context</span><span class="special">(</span><span class="identifier">env</span><span class="special">,</span> <span class="identifier">default_actions</span><span class="special">()));</span> | |
374 | <span class="special">}</span> | |
375 | </pre> | |
376 | <h5> | |
377 | <a name="phoenix.inside.actor.h6"></a> | |
378 | <span><a name="phoenix.inside.actor.result_of__actor"></a></span><a class="link" href="actor.html#phoenix.inside.actor.result_of__actor">result_of::actor</a> | |
379 | </h5> | |
380 | <p> | |
381 | For reasons of symmetry to the family of <code class="computeroutput"><span class="identifier">actor</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code> there is a special metafunction usable | |
382 | for actor result type calculation named <code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">actor</span></code>. | |
383 | This metafunction allows us to directly specify the types of the parameters | |
384 | to be passed to the <code class="computeroutput"><span class="identifier">actor</span><span class="special">::</span><span class="keyword">operator</span><span class="special">()</span></code> function. Here's a typical <code class="computeroutput"><span class="identifier">actor_result</span></code> that accepts two arguments: | |
385 | </p> | |
386 | <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">result_of</span> | |
387 | <span class="special">{</span> | |
388 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T1</span><span class="special">></span> | |
389 | <span class="keyword">struct</span> <span class="identifier">actor</span> | |
390 | <span class="special">{</span> | |
391 | <span class="keyword">typedef</span> <span class="identifier">fusion</span><span class="special">::</span><span class="identifier">vector2</span><span class="special"><</span><span class="identifier">T0</span><span class="special">,</span> <span class="identifier">T1</span><span class="special">></span> <span class="identifier">env_tpe</span><span class="special">;</span> | |
392 | <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">result_of</span><span class="special">::</span><span class="identifier">context</span><span class="special"><</span><span class="identifier">env_type</span><span class="special">,</span> <span class="identifier">default_actions</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">ctx_type</span> | |
393 | <span class="keyword">typedef</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">result_of</span><span class="special"><</span><span class="identifier">evaluator</span><span class="special">(</span><span class="identifier">Expr</span> <span class="keyword">const</span><span class="special">&,</span> <span class="identifier">ctx_type</span><span class="special">)>::</span><span class="identifier">type</span> <span class="identifier">type</span><span class="special">;</span> | |
394 | <span class="special">};</span> | |
395 | <span class="special">}</span> | |
396 | </pre> | |
397 | </div> | |
398 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
399 | <td align="left"></td> | |
400 | <td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas | |
401 | Heller, John Fletcher<p> | |
402 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
403 | file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) | |
404 | </p> | |
405 | </div></td> | |
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