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  25 <div class="section">
  26 <div class="titlepage"><div><div><h4 class="title">
  27 <a name="spirit_repository.qi_components.nonterminal.subrule"></a><a class="link" href="subrule.html" title="Qi subrules">Qi
  28         subrules</a>
  29 </h4></div></div></div>
  30 <h6>
  31 <a name="spirit_repository.qi_components.nonterminal.subrule.h0"></a>
  32           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.description"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.description">Description</a>
  33         </h6>
  34 <p>
  35           The <span class="emphasis"><em>Spirit.Qi</em></span> <code class="computeroutput"><span class="identifier">subrule</span></code>
  36           is a component allowing to create a named parser, and to refer to it by
  37           name -- much like rules and grammars. It is in fact a fully static version
  38           of the rule.
  39         </p>
  40 <p>
  41           The strength of subrules is performance. Replacing some rules with subrules
  42           can make a parser slightly faster (see <a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.performance">Performance</a>
  43           below for measurements). The reason is that subrules allow aggressive inlining
  44           by the C++ compiler, whereas the implementation of rules is based on a
  45           virtual function call which, depending on the compiler, can have some run-time
  46           overhead and stop inlining.
  47         </p>
  48 <p>
  49           The weaknesses of subrules are:
  50         </p>
  51 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  52 <li class="listitem">
  53               subrules can only be defined and used within the same parser expression.
  54               A subrule cannot be defined at one location, and then used in another
  55               location.
  56             </li>
  57 <li class="listitem">
  58               subrules put a massive strain on the C++ compiler. They increase compile
  59               times and memory usage during compilation, and also increase the risk
  60               of hitting compiler limits and/or bugs.
  61             </li>
  62 </ul></div>
  63 <p>
  64 </p>
  65 <pre class="programlisting"><span class="identifier">entry</span> <span class="special">=</span> <span class="special">(</span>
  66     <span class="identifier">expression</span> <span class="special">=</span>
  67         <span class="identifier">term</span>
  68         <span class="special">&gt;&gt;</span> <span class="special">*(</span>   <span class="special">(</span><span class="char">'+'</span> <span class="special">&gt;&gt;</span> <span class="identifier">term</span><span class="special">)</span>
  69             <span class="special">|</span>   <span class="special">(</span><span class="char">'-'</span> <span class="special">&gt;&gt;</span> <span class="identifier">term</span><span class="special">)</span>
  70             <span class="special">)</span>
  71
  72   <span class="special">,</span> <span class="identifier">term</span> <span class="special">=</span>
  73         <span class="identifier">factor</span>
  74         <span class="special">&gt;&gt;</span> <span class="special">*(</span>   <span class="special">(</span><span class="char">'*'</span> <span class="special">&gt;&gt;</span> <span class="identifier">factor</span><span class="special">)</span>
  75             <span class="special">|</span>   <span class="special">(</span><span class="char">'/'</span> <span class="special">&gt;&gt;</span> <span class="identifier">factor</span><span class="special">)</span>
  76             <span class="special">)</span>
  77
  78   <span class="special">,</span> <span class="identifier">factor</span> <span class="special">=</span>
  79         <span class="identifier">uint_</span>
  80         <span class="special">|</span>   <span class="char">'('</span> <span class="special">&gt;&gt;</span> <span class="identifier">expression</span> <span class="special">&gt;&gt;</span> <span class="char">')'</span>
  81         <span class="special">|</span>   <span class="special">(</span><span class="char">'-'</span> <span class="special">&gt;&gt;</span> <span class="identifier">factor</span><span class="special">)</span>
  82         <span class="special">|</span>   <span class="special">(</span><span class="char">'+'</span> <span class="special">&gt;&gt;</span> <span class="identifier">factor</span><span class="special">)</span>
  83 <span class="special">);</span>
  84 </pre>
  85 <p>
  86         </p>
  87 <p>
  88           The example above can be found here: <a href="../../../../../example/qi/calc1_sr.cpp" target="_top">../../example/qi/calc1_sr.cpp</a>
  89         </p>
  90 <p>
  91           As shown in this code snippet (an extract from the calc1_sr example), subrules
  92           can be freely mixed with rules and grammars. Here, a group of 3 subrules
  93           (<code class="computeroutput"><span class="identifier">expression</span></code>, <code class="computeroutput"><span class="identifier">term</span></code>, <code class="computeroutput"><span class="identifier">factor</span></code>)
  94           is assigned to a rule (named <code class="computeroutput"><span class="identifier">entry</span></code>).
  95           This means that parts of a parser can use subrules (typically the innermost,
  96           most performance-critical parts), whereas the rest can use rules and grammars.
  97         </p>
  98 <h6>
  99 <a name="spirit_repository.qi_components.nonterminal.subrule.h1"></a>
 100           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.header"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.header">Header</a>
 101         </h6>
 102 <pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/repository/home/qi/nonterminal/subrule.hpp&gt;</span>
 103 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">repository</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_subrule</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 104 </pre>
 105 <h6>
 106 <a name="spirit_repository.qi_components.nonterminal.subrule.h2"></a>
 107           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.synopsis__declaration_"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.synopsis__declaration_">Synopsis
 108           (declaration)</a>
 109         </h6>
 110 <pre class="programlisting"><span class="identifier">subrule</span><span class="special">&lt;</span><span class="identifier">ID</span><span class="special">,</span> <span class="identifier">A1</span><span class="special">,</span> <span class="identifier">A2</span><span class="special">&gt;</span> <span class="identifier">sr</span><span class="special">(</span><span class="identifier">name</span><span class="special">);</span>
 111 </pre>
 112 <h6>
 113 <a name="spirit_repository.qi_components.nonterminal.subrule.h3"></a>
 114           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.parameters__declaration_"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.parameters__declaration_">Parameters
 115           (declaration)</a>
 116         </h6>
 117 <div class="informaltable"><table class="table">
 118 <colgroup>
 119 <col>
 120 <col>
 121 </colgroup>
 122 <thead><tr>
 123 <th>
 124                   <p>
 125                     Parameter
 126                   </p>
 127                 </th>
 128 <th>
 129                   <p>
 130                     Description
 131                   </p>
 132                 </th>
 133 </tr></thead>
 134 <tbody>
 135 <tr>
 136 <td>
 137                   <p>
 138                     <code class="computeroutput"><span class="identifier">ID</span></code>
 139                   </p>
 140                 </td>
 141 <td>
 142                   <p>
 143                     Required numeric argument. Gives the subrule a unique 'identification
 144                     tag'.
 145                   </p>
 146                 </td>
 147 </tr>
 148 <tr>
 149 <td>
 150                   <p>
 151                     <code class="computeroutput"><span class="identifier">A1</span></code>, <code class="computeroutput"><span class="identifier">A2</span></code>
 152                   </p>
 153                 </td>
 154 <td>
 155                   <p>
 156                     Optional types, can be specified in any order. Can be one of
 157                     1. signature, 2. locals (see rules reference for more information
 158                     on those parameters).
 159                   </p>
 160                   <p>
 161                     Note that the skipper type need not be specified in the parameters,
 162                     unlike with grammars and rules. Subrules will automatically use
 163                     the skipper type which is in effect when they are invoked.
 164                   </p>
 165                 </td>
 166 </tr>
 167 <tr>
 168 <td>
 169                   <p>
 170                     <code class="computeroutput"><span class="identifier">name</span></code>
 171                   </p>
 172                 </td>
 173 <td>
 174                   <p>
 175                     Optional string. Gives the subrule a name, useful for debugging
 176                     and error handling.
 177                   </p>
 178                 </td>
 179 </tr>
 180 </tbody>
 181 </table></div>
 182 <h6>
 183 <a name="spirit_repository.qi_components.nonterminal.subrule.h4"></a>
 184           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.synopsis__usage_"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.synopsis__usage_">Synopsis
 185           (usage)</a>
 186         </h6>
 187 <p>
 188           Subrules are defined and used within groups, typically (and by convention)
 189           enclosed inside parentheses.
 190         </p>
 191 <pre class="programlisting"><span class="comment">// Group containing N subrules</span>
 192 <span class="special">(</span>
 193     <span class="identifier">sr1</span> <span class="special">=</span> <span class="identifier">expr1</span>
 194   <span class="special">,</span> <span class="identifier">sr2</span> <span class="special">=</span> <span class="identifier">expr2</span>
 195   <span class="special">,</span> <span class="special">...</span> <span class="comment">// Any number of subrules</span>
 196 <span class="special">}</span>
 197 </pre>
 198 <p>
 199           The IDs of all subrules defined within the same group must be different.
 200           It is an error to define several subrules with the same ID (or to define
 201           the same subrule multiple times) in the same group.
 202         </p>
 203 <pre class="programlisting"><span class="comment">// Auto-subrules and inherited attributes</span>
 204 <span class="special">(</span>
 205     <span class="identifier">srA</span> <span class="special">%=</span> <span class="identifier">exprA</span> <span class="special">&gt;&gt;</span> <span class="identifier">srB</span> <span class="special">&gt;&gt;</span> <span class="identifier">srC</span><span class="special">(</span><span class="identifier">c1</span><span class="special">,</span> <span class="identifier">c2</span><span class="special">,</span> <span class="special">...)</span> <span class="comment">// Arguments to subrule srC</span>
 206   <span class="special">,</span> <span class="identifier">srB</span> <span class="special">%=</span> <span class="identifier">exprB</span>
 207   <span class="special">,</span> <span class="identifier">srC</span>  <span class="special">=</span> <span class="identifier">exprC</span>
 208   <span class="special">,</span> <span class="special">...</span>
 209 <span class="special">)(</span><span class="identifier">a1</span><span class="special">,</span> <span class="identifier">a2</span><span class="special">,</span> <span class="special">...)</span>         <span class="comment">// Arguments to group, i.e. to start subrule srA</span>
 210 </pre>
 211 <h6>
 212 <a name="spirit_repository.qi_components.nonterminal.subrule.h5"></a>
 213           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.parameters__usage_"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.parameters__usage_">Parameters
 214           (usage)</a>
 215         </h6>
 216 <div class="informaltable"><table class="table">
 217 <colgroup>
 218 <col>
 219 <col>
 220 </colgroup>
 221 <thead><tr>
 222 <th>
 223                   <p>
 224                     Parameter
 225                   </p>
 226                 </th>
 227 <th>
 228                   <p>
 229                     Description
 230                   </p>
 231                 </th>
 232 </tr></thead>
 233 <tbody>
 234 <tr>
 235 <td>
 236                   <p>
 237                     <code class="computeroutput"><span class="identifier">sr1</span></code>, <code class="computeroutput"><span class="identifier">sr2</span></code>
 238                   </p>
 239                 </td>
 240 <td>
 241                   <p>
 242                     Subrules with different IDs.
 243                   </p>
 244                 </td>
 245 </tr>
 246 <tr>
 247 <td>
 248                   <p>
 249                     <code class="computeroutput"><span class="identifier">expr1</span></code>, <code class="computeroutput"><span class="identifier">expr2</span></code>
 250                   </p>
 251                 </td>
 252 <td>
 253                   <p>
 254                     Parser expressions. Can include <code class="computeroutput"><span class="identifier">sr1</span></code>
 255                     and <code class="computeroutput"><span class="identifier">sr2</span></code>, as well
 256                     as any other valid parser expressions.
 257                   </p>
 258                 </td>
 259 </tr>
 260 <tr>
 261 <td>
 262                   <p>
 263                     <code class="computeroutput"><span class="identifier">srA</span></code>
 264                   </p>
 265                 </td>
 266 <td>
 267                   <p>
 268                     Subrule with a synthesized attribute and inherited attributes.
 269                   </p>
 270                 </td>
 271 </tr>
 272 <tr>
 273 <td>
 274                   <p>
 275                     <code class="computeroutput"><span class="identifier">srB</span></code>
 276                   </p>
 277                 </td>
 278 <td>
 279                   <p>
 280                     Subrule with a synthesized attribute.
 281                   </p>
 282                 </td>
 283 </tr>
 284 <tr>
 285 <td>
 286                   <p>
 287                     <code class="computeroutput"><span class="identifier">srC</span></code>
 288                   </p>
 289                 </td>
 290 <td>
 291                   <p>
 292                     Subrule with inherited attributes.
 293                   </p>
 294                 </td>
 295 </tr>
 296 <tr>
 297 <td>
 298                   <p>
 299                     <code class="computeroutput"><span class="identifier">exprA</span></code>, <code class="computeroutput"><span class="identifier">exprB</span></code>, <code class="computeroutput"><span class="identifier">exprC</span></code>
 300                   </p>
 301                 </td>
 302 <td>
 303                   <p>
 304                     Parser expressions.
 305                   </p>
 306                 </td>
 307 </tr>
 308 <tr>
 309 <td>
 310                   <p>
 311                     <code class="computeroutput"><span class="identifier">a1</span></code>, <code class="computeroutput"><span class="identifier">a2</span></code>
 312                   </p>
 313                 </td>
 314 <td>
 315                   <p>
 316                     Arguments passed to the subrule group. They are passed as inherited
 317                     attributes to the group's start subrule, <code class="computeroutput"><span class="identifier">srA</span></code>.
 318                   </p>
 319                 </td>
 320 </tr>
 321 <tr>
 322 <td>
 323                   <p>
 324                     <code class="computeroutput"><span class="identifier">c1</span></code>, <code class="computeroutput"><span class="identifier">c2</span></code>
 325                   </p>
 326                 </td>
 327 <td>
 328                   <p>
 329                     Arguments passed as inherited attributes to subrule <code class="computeroutput"><span class="identifier">srC</span></code>.
 330                   </p>
 331                 </td>
 332 </tr>
 333 </tbody>
 334 </table></div>
 335 <h6>
 336 <a name="spirit_repository.qi_components.nonterminal.subrule.h6"></a>
 337           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.groups"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.groups">Groups</a>
 338         </h6>
 339 <p>
 340           A subrule group (a set of subrule definitions) is a parser, which can be
 341           used anywhere in a parser expression (in assignments to rules, as well
 342           as directly in arguments to functions such as <code class="computeroutput"><span class="identifier">parse</span></code>).
 343           In a group, parsing proceeds from the start subrule, which is the first
 344           (topmost) subrule defined in that group. In the two groups in the synopsis
 345           above, <code class="computeroutput"><span class="identifier">sr1</span></code> and <code class="computeroutput"><span class="identifier">srA</span></code> are the start subrules respectively
 346           -- for example when the first subrule group is called forth, the <code class="computeroutput"><span class="identifier">sr1</span></code> subrule is called.
 347         </p>
 348 <p>
 349           A subrule can only be used in a group which defines it. Groups can be viewed
 350           as scopes: a definition of a subrule is limited to its enclosing group.
 351         </p>
 352 <pre class="programlisting"><span class="identifier">rule</span><span class="special">&lt;</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*&gt;</span> <span class="identifier">r1</span><span class="special">,</span> <span class="identifier">r2</span><span class="special">,</span> <span class="identifier">r3</span><span class="special">;</span>
 353 <span class="identifier">subrule</span><span class="special">&lt;</span><span class="number">1</span><span class="special">&gt;</span> <span class="identifier">sr1</span><span class="special">;</span>
 354 <span class="identifier">subrule</span><span class="special">&lt;</span><span class="number">2</span><span class="special">&gt;</span> <span class="identifier">sr2</span><span class="special">;</span>
 355
 356 <span class="identifier">r1</span> <span class="special">=</span>
 357         <span class="special">(</span> <span class="identifier">sr1</span> <span class="special">=</span> <span class="char">'a'</span> <span class="special">&gt;&gt;</span> <span class="identifier">int_</span> <span class="special">)</span>       <span class="comment">// First group in r1.</span>
 358     <span class="special">&gt;&gt;</span>  <span class="special">(</span> <span class="identifier">sr2</span> <span class="special">=</span> <span class="special">+</span><span class="identifier">sr1</span> <span class="special">)</span>              <span class="comment">// Second group in r1.</span>
 359     <span class="comment">//           ^^^</span>
 360     <span class="comment">// DOES NOT COMPILE: sr1 is not defined in this</span>
 361     <span class="comment">// second group, it cannot be used here (its</span>
 362     <span class="comment">// previous definition is out of scope).</span>
 363 <span class="special">;</span>
 364
 365 <span class="identifier">r2</span> <span class="special">=</span>
 366         <span class="special">(</span> <span class="identifier">sr1</span> <span class="special">=</span> <span class="char">'a'</span> <span class="special">&gt;&gt;</span> <span class="identifier">int_</span> <span class="special">)</span>       <span class="comment">// Only group in r2.</span>
 367     <span class="special">&gt;&gt;</span>  <span class="identifier">sr1</span>
 368     <span class="comment">//  ^^^</span>
 369     <span class="comment">// DOES NOT COMPILE: not in a subrule group,</span>
 370     <span class="comment">// sr1 cannot be used here (here too, its</span>
 371     <span class="comment">// previous definition is out of scope).</span>
 372 <span class="special">;</span>
 373
 374 <span class="identifier">r3</span> <span class="special">=</span>
 375         <span class="special">(</span> <span class="identifier">sr1</span> <span class="special">=</span> <span class="char">'x'</span> <span class="special">&gt;&gt;</span> <span class="identifier">double_</span> <span class="special">)</span>    <span class="comment">// Another group. The same subrule `sr1`</span>
 376                                     <span class="comment">// can have another, independent</span>
 377                                     <span class="comment">// definition in this group.</span>
 378 <span class="special">;</span>
 379 </pre>
 380 <h6>
 381 <a name="spirit_repository.qi_components.nonterminal.subrule.h7"></a>
 382           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.attributes"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.attributes">Attributes</a>
 383         </h6>
 384 <p>
 385           A subrule has the same behavior as a rule with respect to attributes. In
 386           particular:
 387         </p>
 388 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 389 <li class="listitem">
 390               the type of its synthesized attribute is the one specified in the subrule's
 391               signature, if any. Otherwise it is <code class="computeroutput"><span class="identifier">unused_type</span></code>.
 392             </li>
 393 <li class="listitem">
 394               the types of its inherited attributes are the ones specified in the
 395               subrule's signature, if any. Otherwise the subrule has no inherited
 396               attributes.
 397             </li>
 398 <li class="listitem">
 399               an auto-subrule can be defined by assigning it with the <code class="computeroutput"><span class="special">%=</span></code> syntax. In this case, the RHS parser's
 400               attribute is automatically propagated to the subrule's synthesized
 401               attribute.
 402             </li>
 403 <li class="listitem">
 404               the Phoenix placeholders <code class="computeroutput"><span class="identifier">_val</span></code>,
 405               <code class="computeroutput"><span class="identifier">_r1</span></code>, <code class="computeroutput"><span class="identifier">_r2</span></code>, ... are available to refer to
 406               the subrule's synthesized and inherited attributes, if present.
 407             </li>
 408 </ul></div>
 409 <h6>
 410 <a name="spirit_repository.qi_components.nonterminal.subrule.h8"></a>
 411           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.locals"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.locals">Locals</a>
 412         </h6>
 413 <p>
 414           A subrule has the same behavior as a rule with respect to locals. In particular,
 415           the Phoenix placeholders <code class="computeroutput"><span class="identifier">_a</span></code>,
 416           <code class="computeroutput"><span class="identifier">_b</span></code>, ... are available to
 417           refer to the subrule's locals, if present.
 418         </p>
 419 <h6>
 420 <a name="spirit_repository.qi_components.nonterminal.subrule.h9"></a>
 421           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.example"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.example">Example</a>
 422         </h6>
 423 <p>
 424           Some includes:
 425         </p>
 426 <p>
 427 </p>
 428 <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 429 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">repository</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_subrule</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 430 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">phoenix_core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 431 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">phoenix_operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 432 </pre>
 433 <p>
 434         </p>
 435 <p>
 436           Some using declarations:
 437         </p>
 438 <p>
 439 </p>
 440 <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">qi</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">qi</span><span class="special">;</span>
 441 <span class="keyword">namespace</span> <span class="identifier">repo</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">repository</span><span class="special">;</span>
 442 <span class="keyword">namespace</span> <span class="identifier">ascii</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">ascii</span><span class="special">;</span>
 443 </pre>
 444 <p>
 445         </p>
 446 <p>
 447           A grammar containing only one rule, defined with a group of 5 subrules:
 448         </p>
 449 <p>
 450 </p>
 451 <pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">&gt;</span>
 452 <span class="keyword">struct</span> <span class="identifier">mini_xml_grammar</span>
 453   <span class="special">:</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">grammar</span><span class="special">&lt;</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml</span><span class="special">(),</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">&gt;</span>
 454 <span class="special">{</span>
 455     <span class="identifier">mini_xml_grammar</span><span class="special">()</span>
 456       <span class="special">:</span> <span class="identifier">mini_xml_grammar</span><span class="special">::</span><span class="identifier">base_type</span><span class="special">(</span><span class="identifier">entry</span><span class="special">)</span>
 457     <span class="special">{</span>
 458         <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">lit</span><span class="special">;</span>
 459         <span class="keyword">using</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">lexeme</span><span class="special">;</span>
 460         <span class="keyword">using</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span>
 461         <span class="keyword">using</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">string</span><span class="special">;</span>
 462         <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">labels</span><span class="special">;</span>
 463
 464         <span class="identifier">entry</span> <span class="special">%=</span> <span class="special">(</span>
 465             <span class="identifier">xml</span> <span class="special">%=</span>
 466                     <span class="identifier">start_tag</span><span class="special">[</span><span class="identifier">_a</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</span>
 467                 <span class="special">&gt;&gt;</span>  <span class="special">*</span><span class="identifier">node</span>
 468                 <span class="special">&gt;&gt;</span>  <span class="identifier">end_tag</span><span class="special">(</span><span class="identifier">_a</span><span class="special">)</span>
 469
 470           <span class="special">,</span> <span class="identifier">node</span> <span class="special">%=</span> <span class="identifier">xml</span> <span class="special">|</span> <span class="identifier">text</span>
 471
 472           <span class="special">,</span> <span class="identifier">text</span> <span class="special">%=</span> <span class="identifier">lexeme</span><span class="special">[+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'&lt;'</span><span class="special">)]</span>
 473
 474           <span class="special">,</span> <span class="identifier">start_tag</span> <span class="special">%=</span>
 475                     <span class="char">'&lt;'</span>
 476                 <span class="special">&gt;&gt;</span>  <span class="special">!</span><span class="identifier">lit</span><span class="special">(</span><span class="char">'/'</span><span class="special">)</span>
 477                 <span class="special">&gt;&gt;</span>  <span class="identifier">lexeme</span><span class="special">[+(</span><span class="identifier">char_</span> <span class="special">-</span> <span class="char">'&gt;'</span><span class="special">)]</span>
 478                 <span class="special">&gt;&gt;</span>  <span class="char">'&gt;'</span>
 479
 480           <span class="special">,</span> <span class="identifier">end_tag</span> <span class="special">%=</span>
 481                     <span class="string">"&lt;/"</span>
 482                 <span class="special">&gt;&gt;</span>  <span class="identifier">string</span><span class="special">(</span><span class="identifier">_r1</span><span class="special">)</span>
 483                 <span class="special">&gt;&gt;</span>  <span class="char">'&gt;'</span>
 484         <span class="special">);</span>
 485     <span class="special">}</span>
 486
 487     <span class="identifier">qi</span><span class="special">::</span><span class="identifier">rule</span><span class="special">&lt;</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">mini_xml</span><span class="special">(),</span> <span class="identifier">ascii</span><span class="special">::</span><span class="identifier">space_type</span><span class="special">&gt;</span> <span class="identifier">entry</span><span class="special">;</span>
 488
 489     <span class="identifier">repo</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">subrule</span><span class="special">&lt;</span><span class="number">0</span><span class="special">,</span> <span class="identifier">mini_xml</span><span class="special">(),</span> <span class="identifier">qi</span><span class="special">::</span><span class="identifier">locals</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&gt;</span> <span class="special">&gt;</span> <span class="identifier">xml</span><span class="special">;</span>
 490     <span class="identifier">repo</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">subrule</span><span class="special">&lt;</span><span class="number">1</span><span class="special">,</span> <span class="identifier">mini_xml_node</span><span class="special">()&gt;</span> <span class="identifier">node</span><span class="special">;</span>
 491     <span class="identifier">repo</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">subrule</span><span class="special">&lt;</span><span class="number">2</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">()&gt;</span> <span class="identifier">text</span><span class="special">;</span>
 492     <span class="identifier">repo</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">subrule</span><span class="special">&lt;</span><span class="number">3</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">()&gt;</span> <span class="identifier">start_tag</span><span class="special">;</span>
 493     <span class="identifier">repo</span><span class="special">::</span><span class="identifier">qi</span><span class="special">::</span><span class="identifier">subrule</span><span class="special">&lt;</span><span class="number">4</span><span class="special">,</span> <span class="keyword">void</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">)&gt;</span> <span class="identifier">end_tag</span><span class="special">;</span>
 494 <span class="special">};</span>
 495 </pre>
 496 <p>
 497         </p>
 498 <p>
 499           The definitions of the <code class="computeroutput"><span class="identifier">mini_xml</span></code>
 500           and <code class="computeroutput"><span class="identifier">mini_xml_node</span></code> data
 501           structures are not shown here. The full example above can be found here:
 502           <a href="../../../../../example/qi/mini_xml2_sr.cpp" target="_top">../../example/qi/mini_xml2_sr.cpp</a>
 503         </p>
 504 <h6>
 505 <a name="spirit_repository.qi_components.nonterminal.subrule.h10"></a>
 506           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.performance"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.performance">Performance</a>
 507         </h6>
 508 <p>
 509           This table compares run-time and compile-time performance when converting
 510           examples to subrules, with various compilers.
 511         </p>
 512 <div class="table">
 513 <a name="spirit_repository.qi_components.nonterminal.subrule.t0"></a><p class="title"><b>Table&#160;2.&#160;Subrules performance</b></p>
 514 <div class="table-contents"><table class="table" summary="Subrules performance">
 515 <colgroup>
 516 <col>
 517 <col>
 518 <col>
 519 <col>
 520 <col>
 521 </colgroup>
 522 <thead><tr>
 523 <th>
 524                   <p>
 525                     Example
 526                   </p>
 527                 </th>
 528 <th>
 529                   <p>
 530                     Compiler
 531                   </p>
 532                 </th>
 533 <th>
 534                   <p>
 535                     Speed (run-time)
 536                   </p>
 537                 </th>
 538 <th>
 539                   <p>
 540                     Time (compile-time)
 541                   </p>
 542                 </th>
 543 <th>
 544                   <p>
 545                     Memory (compile-time)
 546                   </p>
 547                 </th>
 548 </tr></thead>
 549 <tbody>
 550 <tr>
 551 <td>
 552                   <p>
 553                     calc1_sr
 554                   </p>
 555                 </td>
 556 <td>
 557                   <p>
 558                     gcc 4.4.1
 559                   </p>
 560                 </td>
 561 <td>
 562                   <p>
 563                     +6%
 564                   </p>
 565                 </td>
 566 <td>
 567                   <p>
 568                     n/a
 569                   </p>
 570                 </td>
 571 <td>
 572                   <p>
 573                     n/a
 574                   </p>
 575                 </td>
 576 </tr>
 577 <tr>
 578 <td>
 579                   <p>
 580                     calc1_sr
 581                   </p>
 582                 </td>
 583 <td>
 584                   <p>
 585                     Visual C++ 2008 (VC9)
 586                   </p>
 587                 </td>
 588 <td>
 589                   <p>
 590                     +5%
 591                   </p>
 592                 </td>
 593 <td>
 594                   <p>
 595                     n/a
 596                   </p>
 597                 </td>
 598 <td>
 599                   <p>
 600                     n/a
 601                   </p>
 602                 </td>
 603 </tr>
 604 <tr>
 605 <td>
 606                   <p>
 607                     mini_xml2_sr
 608                   </p>
 609                 </td>
 610 <td>
 611                   <p>
 612                     gcc 3.4.6
 613                   </p>
 614                 </td>
 615 <td>
 616                   <p>
 617                     -1%
 618                   </p>
 619                 </td>
 620 <td>
 621                   <p>
 622                     +54%
 623                   </p>
 624                 </td>
 625 <td>
 626                   <p>
 627                     +32%
 628                   </p>
 629                 </td>
 630 </tr>
 631 <tr>
 632 <td>
 633                   <p>
 634                     mini_xml2_sr
 635                   </p>
 636                 </td>
 637 <td>
 638                   <p>
 639                     gcc 4.1.2
 640                   </p>
 641                 </td>
 642 <td>
 643                   <p>
 644                     +5%
 645                   </p>
 646                 </td>
 647 <td>
 648                   <p>
 649                     +58%
 650                   </p>
 651                 </td>
 652 <td>
 653                   <p>
 654                     +25%
 655                   </p>
 656                 </td>
 657 </tr>
 658 <tr>
 659 <td>
 660                   <p>
 661                     mini_xml2_sr
 662                   </p>
 663                 </td>
 664 <td>
 665                   <p>
 666                     gcc 4.4.1
 667                   </p>
 668                 </td>
 669 <td>
 670                   <p>
 671                     +8%
 672                   </p>
 673                 </td>
 674 <td>
 675                   <p>
 676                     +20%
 677                   </p>
 678                 </td>
 679 <td>
 680                   <p>
 681                     +14%
 682                   </p>
 683                 </td>
 684 </tr>
 685 <tr>
 686 <td>
 687                   <p>
 688                     mini_xml2_sr
 689                   </p>
 690                 </td>
 691 <td>
 692                   <p>
 693                     Visual C++ 2005 (VC8) SP1
 694                   </p>
 695                 </td>
 696 <td>
 697                   <p>
 698                     +1%
 699                   </p>
 700                 </td>
 701 <td>
 702                   <p>
 703                     +33%
 704                   </p>
 705                 </td>
 706 <td>
 707                   <p>
 708                     +27%
 709                   </p>
 710                 </td>
 711 </tr>
 712 <tr>
 713 <td>
 714                   <p>
 715                     mini_xml2_sr
 716                   </p>
 717                 </td>
 718 <td>
 719                   <p>
 720                     Visual C++ 2008 (VC9)
 721                   </p>
 722                 </td>
 723 <td>
 724                   <p>
 725                     +9%
 726                   </p>
 727                 </td>
 728 <td>
 729                   <p>
 730                     +52%
 731                   </p>
 732                 </td>
 733 <td>
 734                   <p>
 735                     +40%
 736                   </p>
 737                 </td>
 738 </tr>
 739 </tbody>
 740 </table></div>
 741 </div>
 742 <br class="table-break"><p>
 743           The columns are:
 744         </p>
 745 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 746 <li class="listitem">
 747               <span class="bold"><strong>Speed (run-time)</strong></span>: speed-up of the
 748               parser resulting from the use of subrules (higher is better).
 749             </li>
 750 <li class="listitem">
 751               <span class="bold"><strong>Time (compile-time)</strong></span>: increase in compile
 752               time (lower is better).
 753             </li>
 754 <li class="listitem">
 755               <span class="bold"><strong>Memory (compile-time)</strong></span>: increase in
 756               compiler memory usage (lower is better).
 757             </li>
 758 </ul></div>
 759 <h6>
 760 <a name="spirit_repository.qi_components.nonterminal.subrule.h11"></a>
 761           <span class="phrase"><a name="spirit_repository.qi_components.nonterminal.subrule.notes"></a></span><a class="link" href="subrule.html#spirit_repository.qi_components.nonterminal.subrule.notes">Notes</a>
 762         </h6>
 763 <p>
 764           Subrules push the C++ compiler hard. A group of subrules is a single C++
 765           expression. Current C++ compilers cannot handle very complex expressions
 766           very well. One restricting factor is the typical compiler's limit on template
 767           recursion depth. Some, but not all, compilers allow this limit to be configured.
 768         </p>
 769 <p>
 770           g++'s maximum can be set using a compiler flag: <code class="computeroutput"><span class="special">-</span><span class="identifier">ftemplate</span><span class="special">-</span><span class="identifier">depth</span></code>. Set this appropriately if you
 771           use relatively complex subrules.
 772         </p>
 773 </div>
 774 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 775 <td align="left"></td>
 776 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
 777         Distributed under the Boost Software License, Version 1.0. (See accompanying
 778         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>)
 779       </p>
 780 </div></td>
 781 </tr></table>
 782 <hr>
 783 <div class="spirit-nav">
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