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1 | <html> |
| 2 | <head> | |
| 3 | <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> | |
| 4 | <title>Phoenix Expressions</title> | |
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| 24 | </div> | |
| 25 | <div class="section"> | |
| 26 | <div class="titlepage"><div><div><h3 class="title"> | |
| 27 | <a name="phoenix.inside.expression"></a><a class="link" href="expression.html" title="Phoenix Expressions">Phoenix Expressions</a> | |
| 28 | </h3></div></div></div> | |
| 29 | <div class="toc"><dl><dt><span class="section"><a href="expression/boilerplate_macros.html">Boilerplate | |
| 30 | Macros</a></span></dt></dl></div> | |
| 31 | <p> | |
| 32 | A Phoenix Expression is a model of the <a href="http://www.boost.org/doc/libs/release/doc/html/Expr.html" target="_top">Proto | |
| 33 | Expression</a> Concept. These expressions are wrapped inside an <a class="link" href="actor.html" title="Actors in Detail">Actor</a> template. The <code class="computeroutput"><span class="identifier">actor</span></code> | |
| 34 | provides the function call operator which evaluates the expressions. The | |
| 35 | <code class="computeroutput"><span class="identifier">actor</span></code> is the domain specific | |
| 36 | wrapper around Phoenix expressions. | |
| 37 | </p> | |
| 38 | <p> | |
| 39 | By design, Phoenix Expressions do not carry any information on how they will | |
| 40 | be evaluated later on. They are the data structure on which the <code class="computeroutput"><span class="identifier">Actions</span></code> will work. | |
| 41 | </p> | |
| 42 | <p> | |
| 43 | The library provides a convenience template to define expressions: | |
| 44 | </p> | |
| 45 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span><span class="special">></span> <span class="identifier">Actor</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Tag</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A0</span><span class="special">,</span> <span class="special">...,</span> <span class="keyword">typename</span> <span class="identifier">A1</span><span class="special">></span> | |
| 46 | <span class="keyword">struct</span> <span class="identifier">expr_ext</span> | |
| 47 | <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">transform</span><span class="special"><</span><span class="identifier">expr_ext</span><span class="special"><</span><span class="identifier">Actor</span><span class="special">,</span> <span class="identifier">Tag</span><span class="special">,</span> <span class="identifier">A0</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">A1</span><span class="special">></span> <span class="special">></span> | |
| 48 | <span class="special">{</span> | |
| 49 | <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span> <span class="identifier">base_expr</span><span class="special">;</span> | |
| 50 | <span class="keyword">typedef</span> <span class="identifier">Actor</span><span class="special"><</span><span class="identifier">base_expr</span><span class="special">></span> <span class="identifier">type</span><span class="special">;</span> | |
| 51 | ||
| 52 | <span class="keyword">typedef</span> <span class="emphasis"><em>unspecified</em></span> <span class="identifier">proto_grammar</span><span class="special">;</span> | |
| 53 | ||
| 54 | <span class="keyword">static</span> <span class="identifier">type</span> <span class="identifier">make</span><span class="special">(</span><span class="identifier">A0</span> <span class="identifier">a0</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">A1</span> <span class="identifier">a1</span><span class="special">);</span> | |
| 55 | <span class="special">};</span> | |
| 56 | ||
| 57 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Tag</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A0</span><span class="special">,</span> <span class="special">...,</span> <span class="keyword">typename</span> <span class="identifier">A1</span><span class="special">></span> | |
| 58 | <span class="keyword">struct</span> <span class="identifier">expr</span> <span class="special">:</span> <span class="identifier">expr_ext</span><span class="special"><</span><span class="identifier">actor</span><span class="special">,</span> <span class="identifier">Tag</span><span class="special">,</span> <span class="identifier">A0</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">A1</span><span class="special">></span> <span class="special">{};</span> | |
| 59 | </pre> | |
| 60 | <p> | |
| 61 | <span class="bold"><strong>Notation</strong></span> | |
| 62 | </p> | |
| 63 | <div class="variablelist"> | |
| 64 | <p class="title"><b></b></p> | |
| 65 | <dl> | |
| 66 | <dt><span class="term"><code class="computeroutput"><span class="identifier">A0</span><span class="special">...</span><span class="identifier">AN</span></code></span></dt> | |
| 67 | <dd><p> | |
| 68 | Child node types | |
| 69 | </p></dd> | |
| 70 | <dt><span class="term"><code class="computeroutput"><span class="identifier">a0</span><span class="special">...</span><span class="identifier">aN</span></code></span></dt> | |
| 71 | <dd><p> | |
| 72 | Child node objects | |
| 73 | </p></dd> | |
| 74 | <dt><span class="term"><code class="computeroutput"><span class="identifier">G0</span><span class="special">...</span><span class="identifier">GN</span></code></span></dt> | |
| 75 | <dd><p> | |
| 76 | <a href="http://www.boost.org/doc/libs/release/libs/proto/index.html" target="_top">Boost.Proto</a> | |
| 77 | grammar types | |
| 78 | </p></dd> | |
| 79 | </dl> | |
| 80 | </div> | |
| 81 | <p> | |
| 82 | <span class="bold"><strong>Expression Semantics</strong></span> | |
| 83 | </p> | |
| 84 | <div class="informaltable"><table class="table"> | |
| 85 | <colgroup> | |
| 86 | <col> | |
| 87 | <col> | |
| 88 | </colgroup> | |
| 89 | <thead><tr> | |
| 90 | <th> | |
| 91 | <p> | |
| 92 | Expression | |
| 93 | </p> | |
| 94 | </th> | |
| 95 | <th> | |
| 96 | <p> | |
| 97 | Semantics | |
| 98 | </p> | |
| 99 | </th> | |
| 100 | </tr></thead> | |
| 101 | <tbody> | |
| 102 | <tr> | |
| 103 | <td> | |
| 104 | <p> | |
| 105 | <code class="computeroutput"><span class="identifier">expr</span><span class="special"><</span><span class="identifier">Tag</span><span class="special">,</span> | |
| 106 | <span class="identifier">A0</span><span class="special">...</span><span class="identifier">AN</span><span class="special">>::</span><span class="identifier">type</span></code> | |
| 107 | </p> | |
| 108 | </td> | |
| 109 | <td> | |
| 110 | <p> | |
| 111 | The type of Expression having tag <code class="computeroutput"><span class="identifier">Tag</span></code> | |
| 112 | and <code class="computeroutput"><span class="identifier">A0</span><span class="special">...</span><span class="identifier">AN</span></code> children | |
| 113 | </p> | |
| 114 | </td> | |
| 115 | </tr> | |
| 116 | <tr> | |
| 117 | <td> | |
| 118 | <p> | |
| 119 | <code class="computeroutput"><span class="identifier">expr</span><span class="special"><</span><span class="identifier">Tag</span><span class="special">,</span> | |
| 120 | <span class="identifier">G0</span><span class="special">...</span><span class="identifier">GN</span><span class="special">></span></code> | |
| 121 | </p> | |
| 122 | </td> | |
| 123 | <td> | |
| 124 | <p> | |
| 125 | A <a href="http://www.boost.org/doc/libs/release/libs/proto/index.html" target="_top">Boost.Proto</a> | |
| 126 | grammar and <a href="http://www.boost.org/doc/libs/release/doc/html/boost/proto/pass_through.html" target="_top">Proto | |
| 127 | Pass Through Transform</a> | |
| 128 | </p> | |
| 129 | </td> | |
| 130 | </tr> | |
| 131 | <tr> | |
| 132 | <td> | |
| 133 | <p> | |
| 134 | <code class="computeroutput"><span class="identifier">expr</span><span class="special"><</span><span class="identifier">Tag</span><span class="special">,</span> | |
| 135 | <span class="identifier">A0</span><span class="special">...</span><span class="identifier">AN</span><span class="special">>::</span><span class="identifier">make</span><span class="special">(</span><span class="identifier">a0</span><span class="special">...</span><span class="identifier">aN</span><span class="special">)</span></code> | |
| 136 | </p> | |
| 137 | </td> | |
| 138 | <td> | |
| 139 | <p> | |
| 140 | Returns a Phoenix Expression | |
| 141 | </p> | |
| 142 | </td> | |
| 143 | </tr> | |
| 144 | </tbody> | |
| 145 | </table></div> | |
| 146 | <div class="note"><table border="0" summary="Note"> | |
| 147 | <tr> | |
| 148 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> | |
| 149 | <th align="left">Note</th> | |
| 150 | </tr> | |
| 151 | <tr><td align="left" valign="top"><p> | |
| 152 | You might have noticed the template template argument <code class="computeroutput"><span class="identifier">Actor</span></code> | |
| 153 | used in <code class="computeroutput"><span class="identifier">expr_ext</span></code>. This | |
| 154 | can be a user supplied custom Actor adding other member functions or objects | |
| 155 | than the default <code class="computeroutput"><span class="identifier">actor</span></code> | |
| 156 | template. See <a class="link" href="../examples/extending_actors.html" title="Extending Actors">Extending | |
| 157 | Actors</a> for more details. | |
| 158 | </p></td></tr> | |
| 159 | </table></div> | |
| 160 | <h5> | |
| 161 | <a name="phoenix.inside.expression.h0"></a> | |
| 162 | <span><a name="phoenix.inside.expression.meta_grammar"></a></span><a class="link" href="expression.html#phoenix.inside.expression.meta_grammar">meta_grammar</a> | |
| 163 | </h5> | |
| 164 | <p> | |
| 165 | Defining expressions is only part of the game to make it a valid Phoenix | |
| 166 | Expression. In order to use the expressions in the Phoenix domain, we need | |
| 167 | to "register" them to our grammar. | |
| 168 | </p> | |
| 169 | <p> | |
| 170 | The <code class="computeroutput"><span class="identifier">meta_grammar</span></code> is a struct | |
| 171 | for exactly that purpose. It is an openly extendable <a href="http://www.boost.org/doc/libs/release/libs/proto/index.html" target="_top">Boost.Proto</a> | |
| 172 | Grammar: | |
| 173 | </p> | |
| 174 | <pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">meta_grammar</span> | |
| 175 | <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">switch_</span><span class="special"><</span><span class="identifier">meta_grammar</span><span class="special">></span> | |
| 176 | <span class="special">{</span> | |
| 177 | <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Tag</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Dummy</span><span class="special">></span> | |
| 178 | <span class="keyword">struct</span> <span class="identifier">case_</span> | |
| 179 | <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">not_</span><span class="special"><</span><span class="identifier">proto</span><span class="special">::</span><span class="identifier">_</span><span class="special">></span> | |
| 180 | <span class="special">{};</span> | |
| 181 | <span class="special">};</span> | |
| 182 | </pre> | |
| 183 | <p> | |
| 184 | As you can see, by default the <code class="computeroutput"><span class="identifier">meta_grammar</span></code> | |
| 185 | matches nothing. With every <a class="link" href="../modules.html" title="Modules">Module</a> | |
| 186 | you include this grammar gets extended by various expressions. | |
| 187 | </p> | |
| 188 | <h5> | |
| 189 | <a name="phoenix.inside.expression.h1"></a> | |
| 190 | <span><a name="phoenix.inside.expression.example"></a></span><a class="link" href="expression.html#phoenix.inside.expression.example">Example</a> | |
| 191 | </h5> | |
| 192 | <p> | |
| 193 | Define an expression: | |
| 194 | </p> | |
| 195 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Lhs</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Rhs</span><span class="special">></span> | |
| 196 | <span class="keyword">struct</span> <span class="identifier">plus</span> | |
| 197 | <span class="special">:</span> <span class="identifier">expr</span><span class="special"><</span><span class="identifier">proto</span><span class="special">::</span><span class="identifier">tag</span><span class="special">::</span><span class="identifier">plus</span><span class="special">,</span> <span class="identifier">Lhs</span><span class="special">,</span> <span class="identifier">Rhs</span><span class="special">></span> | |
| 198 | <span class="special">{};</span> | |
| 199 | </pre> | |
| 200 | <p> | |
| 201 | And add it to the grammar: | |
| 202 | </p> | |
| 203 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><></span> | |
| 204 | <span class="keyword">struct</span> <span class="identifier">meta_grammar</span><span class="special">::</span><span class="identifier">case_</span><span class="special"><</span><span class="identifier">proto</span><span class="special">::</span><span class="identifier">tag</span><span class="special">::</span><span class="identifier">plus</span><span class="special">></span> | |
| 205 | <span class="special">:</span> <span class="identifier">enable_rule</span><span class="special"><</span> | |
| 206 | <span class="identifier">plus</span><span class="special"><</span> | |
| 207 | <span class="identifier">meta_grammar</span> | |
| 208 | <span class="special">,</span> <span class="identifier">meta_grammar</span> | |
| 209 | <span class="special">></span> | |
| 210 | <span class="special">></span> | |
| 211 | <span class="special">{};</span> | |
| 212 | </pre> | |
| 213 | <p> | |
| 214 | Define a generator function to make the life of our potential users easier: | |
| 215 | </p> | |
| 216 | <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Lhs</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Rhs</span><span class="special">></span> | |
| 217 | <span class="keyword">typename</span> <span class="identifier">plus</span><span class="special"><</span><span class="identifier">Lhs</span><span class="special">,</span> <span class="identifier">Rhs</span><span class="special">>::</span><span class="identifier">type</span> | |
| 218 | <span class="identifier">plus</span><span class="special">(</span><span class="identifier">Lhs</span> <span class="keyword">const</span> <span class="special">&</span> <span class="identifier">lhs</span><span class="special">,</span> <span class="identifier">Rhs</span> <span class="keyword">const</span> <span class="special">&</span> <span class="identifier">rhs</span><span class="special">)</span> | |
| 219 | <span class="special">{</span> | |
| 220 | <span class="keyword">return</span> <span class="identifier">expression</span><span class="special">::</span><span class="identifier">plus</span><span class="special"><</span><span class="identifier">Lhs</span><span class="special">,</span> <span class="identifier">Rhs</span><span class="special">>::</span><span class="identifier">make</span><span class="special">(</span><span class="identifier">lhs</span><span class="special">,</span> <span class="identifier">rhs</span><span class="special">);</span> | |
| 221 | <span class="special">}</span> | |
| 222 | </pre> | |
| 223 | <p> | |
| 224 | Look if it really works: | |
| 225 | </p> | |
| 226 | <pre class="programlisting"><span class="identifier">plus</span><span class="special">(</span><span class="number">6</span><span class="special">,</span> <span class="number">5</span><span class="special">)();</span> | |
| 227 | </pre> | |
| 228 | <p> | |
| 229 | returns 11! | |
| 230 | </p> | |
| 231 | <pre class="programlisting"><span class="identifier">proto</span><span class="special">::</span><span class="identifier">display_expr</span><span class="special">(</span><span class="identifier">plus</span><span class="special">(</span><span class="number">5</span><span class="special">,</span> <span class="number">6</span><span class="special">));</span> | |
| 232 | </pre> | |
| 233 | <p> | |
| 234 | prints: | |
| 235 | </p> | |
| 236 | <pre class="programlisting"><span class="identifier">plus</span><span class="special">(</span> | |
| 237 | <span class="identifier">terminal</span><span class="special">(</span><span class="number">6</span><span class="special">)</span> | |
| 238 | <span class="special">,</span> <span class="identifier">terminal</span><span class="special">(</span><span class="number">5</span><span class="special">)</span> | |
| 239 | <span class="special">)</span> | |
| 240 | </pre> | |
| 241 | <p> | |
| 242 | See <a href="../../../../example/define_expression.cpp" target="_top">define_expression.cpp</a> | |
| 243 | for the full example. | |
| 244 | </p> | |
| 245 | <div class="note"><table border="0" summary="Note"> | |
| 246 | <tr> | |
| 247 | <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td> | |
| 248 | <th align="left">Note</th> | |
| 249 | </tr> | |
| 250 | <tr><td align="left" valign="top"><p> | |
| 251 | The example shown here only works because <code class="computeroutput"><span class="identifier">default_actions</span></code> | |
| 252 | knows how to handle an expression having the <code class="computeroutput"><span class="identifier">proto</span><span class="special">::</span><span class="identifier">tag</span><span class="special">::</span><span class="identifier">plus</span></code> | |
| 253 | and two children. This is because <code class="computeroutput"><span class="identifier">default_actions</span></code> | |
| 254 | uses the <code class="computeroutput"><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></code> | |
| 255 | transform to evaluate operators and functions. Learn more about actions | |
| 256 | <a class="link" href="actions.html" title="More on Actions">here</a>. | |
| 257 | </p></td></tr> | |
| 258 | </table></div> | |
| 259 | </div> | |
| 260 | <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> | |
| 261 | <td align="left"></td> | |
| 262 | <td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas | |
| 263 | Heller, John Fletcher<p> | |
| 264 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 265 | 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>) | |
| 266 | </p> | |
| 267 | </div></td> | |
| 268 | </tr></table> | |
| 269 | <hr> | |
| 270 | <div class="spirit-nav"> | |
| 271 | <a accesskey="p" href="actor.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../inside.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="expression/boilerplate_macros.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> | |
| 272 | </div> | |
| 273 | </body> | |
| 274 | </html> |