1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Parser Rule</title> 5<link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../../index.html" title="Spirit 2.5.8"> 8<link rel="up" href="../nonterminal.html" title="Nonterminal Parsers"> 9<link rel="prev" href="../nonterminal.html" title="Nonterminal Parsers"> 10<link rel="next" href="grammar.html" title="Parser Grammar"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="../nonterminal.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../nonterminal.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="grammar.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h5 class="title"> 27<a name="spirit.qi.reference.nonterminal.rule"></a><a class="link" href="rule.html" title="Parser Rule">Parser Rule</a> 28</h5></div></div></div> 29<h6> 30<a name="spirit.qi.reference.nonterminal.rule.h0"></a> 31 <span class="phrase"><a name="spirit.qi.reference.nonterminal.rule.description"></a></span><a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.description">Description</a> 32 </h6> 33<p> 34 The rule is a polymorphic parser that acts as a named placeholder capturing 35 the behavior of a <a class="link" href="../../../abstracts/parsing_expression_grammar.html" title="Parsing Expression Grammar">Parsing 36 Expression Grammar</a> expression assigned to it. Naming a <a class="link" href="../../../abstracts/parsing_expression_grammar.html" title="Parsing Expression Grammar">Parsing 37 Expression Grammar</a> expression allows it to be referenced later 38 and makes it possible for the rule to call itself. This is one of the 39 most important mechanisms and the reason behind the word "recursive" 40 in recursive descent parsing. 41 </p> 42<h6> 43<a name="spirit.qi.reference.nonterminal.rule.h1"></a> 44 <span class="phrase"><a name="spirit.qi.reference.nonterminal.rule.header"></a></span><a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.header">Header</a> 45 </h6> 46<pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/nonterminal/rule.hpp></span> 47<span class="preprocessor">#include</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">include</span><span class="special">/</span><span class="identifier">qi_rule</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 48</pre> 49<p> 50 Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>. 51 </p> 52<h6> 53<a name="spirit.qi.reference.nonterminal.rule.h2"></a> 54 <span class="phrase"><a name="spirit.qi.reference.nonterminal.rule.namespace"></a></span><a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.namespace">Namespace</a> 55 </h6> 56<div class="informaltable"><table class="table"> 57<colgroup><col></colgroup> 58<thead><tr><th> 59 <p> 60 Name 61 </p> 62 </th></tr></thead> 63<tbody><tr><td> 64 <p> 65 <code class="computeroutput"><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><span class="identifier">rule</span></code> 66 </p> 67 </td></tr></tbody> 68</table></div> 69<h6> 70<a name="spirit.qi.reference.nonterminal.rule.h3"></a> 71 <span class="phrase"><a name="spirit.qi.reference.nonterminal.rule.synopsis"></a></span><a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.synopsis">Synopsis</a> 72 </h6> 73<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Iterator</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A1</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A2</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A3</span><span class="special">></span> 74<span class="keyword">struct</span> <span class="identifier">rule</span><span class="special">;</span> 75</pre> 76<h6> 77<a name="spirit.qi.reference.nonterminal.rule.h4"></a> 78 <span class="phrase"><a name="spirit.qi.reference.nonterminal.rule.template_parameters"></a></span><a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.template_parameters">Template 79 parameters</a> 80 </h6> 81<div class="informaltable"><table class="table"> 82<colgroup> 83<col> 84<col> 85<col> 86</colgroup> 87<thead><tr> 88<th> 89 <p> 90 Parameter 91 </p> 92 </th> 93<th> 94 <p> 95 Description 96 </p> 97 </th> 98<th> 99 <p> 100 Default 101 </p> 102 </th> 103</tr></thead> 104<tbody> 105<tr> 106<td> 107 <p> 108 <code class="computeroutput"><span class="identifier">Iterator</span></code> 109 </p> 110 </td> 111<td> 112 <p> 113 The underlying iterator type that the rule is expected to work 114 on. 115 </p> 116 </td> 117<td> 118 <p> 119 none 120 </p> 121 </td> 122</tr> 123<tr> 124<td> 125 <p> 126 <code class="computeroutput"><span class="identifier">A1</span></code>, <code class="computeroutput"><span class="identifier">A2</span></code>, <code class="computeroutput"><span class="identifier">A3</span></code> 127 </p> 128 </td> 129<td> 130 <p> 131 Either <code class="computeroutput"><span class="identifier">Signature</span></code>, 132 <code class="computeroutput"><span class="identifier">Skipper</span></code> or 133 <code class="computeroutput"><span class="identifier">Locals</span></code> in any 134 order. See table below. 135 </p> 136 </td> 137<td> 138 <p> 139 See table below. 140 </p> 141 </td> 142</tr> 143</tbody> 144</table></div> 145<p> 146 Here is more information about the template parameters: 147 </p> 148<div class="informaltable"><table class="table"> 149<colgroup> 150<col> 151<col> 152<col> 153</colgroup> 154<thead><tr> 155<th> 156 <p> 157 Parameter 158 </p> 159 </th> 160<th> 161 <p> 162 Description 163 </p> 164 </th> 165<th> 166 <p> 167 Default 168 </p> 169 </th> 170</tr></thead> 171<tbody> 172<tr> 173<td> 174 <p> 175 <code class="computeroutput"><span class="identifier">Signature</span></code> 176 </p> 177 </td> 178<td> 179 <p> 180 Specifies the rule's synthesized (return value) and inherited 181 attributes (arguments). More on this here: <a class="link" href="../parser_concepts/nonterminal.html" title="Nonterminal"><code class="computeroutput"><span class="identifier">Nonterminal</span></code></a>. 182 </p> 183 </td> 184<td> 185 <p> 186 <code class="computeroutput"><span class="identifier">unused_type</span></code>. 187 When <code class="computeroutput"><span class="identifier">Signature</span></code> 188 defaults to <code class="computeroutput"><span class="identifier">unused_type</span></code>, 189 the effect is the same as specifying a signature of <code class="computeroutput"><span class="keyword">void</span><span class="special">()</span></code> 190 which is also equivalent to <code class="computeroutput"><span class="identifier">unused_type</span><span class="special">()</span></code> 191 </p> 192 </td> 193</tr> 194<tr> 195<td> 196 <p> 197 <code class="computeroutput"><span class="identifier">Skipper</span></code> 198 </p> 199 </td> 200<td> 201 <p> 202 Specifies the rule's skipper parser. Specify this if you want 203 the rule to skip white spaces. If this is not specified, the 204 rule is an "implicit lexeme" and will not skip spaces. 205 "implicit lexeme" rules can still be called with 206 a skipper. In such a case, the rule does a pre-skip just as 207 all lexemes and primitives do. 208 </p> 209 </td> 210<td> 211 <p> 212 <code class="computeroutput"><span class="identifier">unused_type</span></code> 213 </p> 214 </td> 215</tr> 216<tr> 217<td> 218 <p> 219 <code class="computeroutput"><span class="identifier">Locals</span></code> 220 </p> 221 </td> 222<td> 223 <p> 224 Specifies the rule's local variables. See <a class="link" href="../parser_concepts/nonterminal.html" title="Nonterminal"><code class="computeroutput"><span class="identifier">Nonterminal</span></code></a>. 225 </p> 226 </td> 227<td> 228 <p> 229 <code class="computeroutput"><span class="identifier">unused_type</span></code> 230 </p> 231 </td> 232</tr> 233</tbody> 234</table></div> 235<h6> 236<a name="spirit.qi.reference.nonterminal.rule.h5"></a> 237 <span class="phrase"><a name="spirit.qi.reference.nonterminal.rule.model_of"></a></span><a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.model_of">Model 238 of</a> 239 </h6> 240<div class="blockquote"><blockquote class="blockquote"><p> 241 <a class="link" href="../parser_concepts/nonterminal.html" title="Nonterminal"><code class="computeroutput"><span class="identifier">Nonterminal</span></code></a> 242 </p></blockquote></div> 243<div class="variablelist"> 244<p class="title"><b>Notation</b></p> 245<dl class="variablelist"> 246<dt><span class="term"><code class="computeroutput"><span class="identifier">r</span><span class="special">,</span> 247 <span class="identifier">r2</span></code></span></dt> 248<dd><p> 249 Rules 250 </p></dd> 251<dt><span class="term"><code class="computeroutput"><span class="identifier">p</span></code></span></dt> 252<dd><p> 253 A parser expression 254 </p></dd> 255<dt><span class="term"><code class="computeroutput"><span class="identifier">Iterator</span></code></span></dt> 256<dd><p> 257 The underlying iterator type that the rule is expected to work 258 on. 259 </p></dd> 260<dt><span class="term"><code class="computeroutput"><span class="identifier">A1</span></code>, <code class="computeroutput"><span class="identifier">A2</span></code>, <code class="computeroutput"><span class="identifier">A3</span></code></span></dt> 261<dd><p> 262 Either <code class="computeroutput"><span class="identifier">Signature</span></code>, 263 <code class="computeroutput"><span class="identifier">Skipper</span></code> or <code class="computeroutput"><span class="identifier">Locals</span></code> in any order. 264 </p></dd> 265</dl> 266</div> 267<h6> 268<a name="spirit.qi.reference.nonterminal.rule.h6"></a> 269 <span class="phrase"><a name="spirit.qi.reference.nonterminal.rule.expression_semantics"></a></span><a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.expression_semantics">Expression 270 Semantics</a> 271 </h6> 272<p> 273 Semantics of an expression is defined only where it differs from, or 274 is not defined in <a class="link" href="../parser_concepts/nonterminal.html" title="Nonterminal"><code class="computeroutput"><span class="identifier">Nonterminal</span></code></a>. 275 </p> 276<div class="informaltable"><table class="table"> 277<colgroup> 278<col> 279<col> 280</colgroup> 281<thead><tr> 282<th> 283 <p> 284 Expression 285 </p> 286 </th> 287<th> 288 <p> 289 Description 290 </p> 291 </th> 292</tr></thead> 293<tbody> 294<tr> 295<td> 296 <p> 297</p> 298<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">A1</span><span class="special">,</span> <span class="identifier">A2</span><span class="special">,</span> <span class="identifier">A3</span><span class="special">></span> 299 <span class="identifier">r</span><span class="special">(</span><span class="identifier">name</span><span class="special">);</span></pre> 300<p> 301 </p> 302 </td> 303<td> 304 <p> 305 Rule declaration. <code class="computeroutput"><span class="identifier">Iterator</span></code> 306 is required. <code class="computeroutput"><span class="identifier">A1</span><span class="special">,</span> <span class="identifier">A2</span><span class="special">,</span> <span class="identifier">A3</span></code> 307 are optional and can be specified in any order. <code class="computeroutput"><span class="identifier">name</span></code> is an optional string 308 that gives the rule its name, useful for debugging and error 309 handling. 310 </p> 311 </td> 312</tr> 313<tr> 314<td> 315 <p> 316</p> 317<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="identifier">Iterator</span><span class="special">,</span> <span class="identifier">A1</span><span class="special">,</span> <span class="identifier">A2</span><span class="special">,</span> <span class="identifier">A3</span><span class="special">></span> 318 <span class="identifier">r</span><span class="special">(</span><span class="identifier">r2</span><span class="special">);</span></pre> 319<p> 320 </p> 321 </td> 322<td> 323 <p> 324 Copy construct rule <code class="computeroutput"><span class="identifier">r</span></code> 325 from rule <code class="computeroutput"><span class="identifier">r2</span></code>. 326 </p> 327 </td> 328</tr> 329<tr> 330<td> 331 <p> 332 <code class="computeroutput"><span class="identifier">r</span> <span class="special">=</span> 333 <span class="identifier">r2</span><span class="special">;</span></code> 334 </p> 335 </td> 336<td> 337 <p> 338 Assign rule <code class="computeroutput"><span class="identifier">r2</span></code> 339 to <code class="computeroutput"><span class="identifier">r</span></code>. 340 </p> 341 </td> 342</tr> 343<tr> 344<td> 345 <p> 346 <code class="computeroutput"><span class="identifier">r</span><span class="special">.</span><span class="identifier">alias</span><span class="special">()</span></code> 347 </p> 348 </td> 349<td> 350 <p> 351 return an alias of <code class="computeroutput"><span class="identifier">r</span></code>. 352 The alias is a parser that holds a reference to <code class="computeroutput"><span class="identifier">r</span></code>. 353 </p> 354 </td> 355</tr> 356<tr> 357<td> 358 <p> 359 <code class="computeroutput"><span class="identifier">r</span><span class="special">.</span><span class="identifier">copy</span><span class="special">()</span></code> 360 </p> 361 </td> 362<td> 363 <p> 364 Get a copy of <code class="computeroutput"><span class="identifier">r</span></code>. 365 </p> 366 </td> 367</tr> 368<tr> 369<td> 370 <p> 371 <code class="computeroutput"><span class="identifier">r</span> <span class="special">=</span> 372 <span class="identifier">p</span><span class="special">;</span></code> 373 </p> 374 </td> 375<td> 376 <p> 377 Rule definition. This is equivalent to <code class="computeroutput"><span class="identifier">r</span> 378 <span class="special">%=</span> <span class="identifier">p</span></code> 379 (see below) if there are no semantic actions attached anywhere 380 in <code class="computeroutput"><span class="identifier">p</span></code>. 381 </p> 382 </td> 383</tr> 384<tr> 385<td> 386 <p> 387 <code class="computeroutput"><span class="identifier">r</span> <span class="special">%=</span> 388 <span class="identifier">p</span><span class="special">;</span></code> 389 </p> 390 </td> 391<td> 392 <p> 393 Auto-rule definition. The attribute of <code class="computeroutput"><span class="identifier">p</span></code> 394 must be compatible with the synthesized attribute of <code class="computeroutput"><span class="identifier">r</span></code>. If <code class="computeroutput"><span class="identifier">p</span></code> 395 is successful, its attribute is automatically propagated to 396 <code class="computeroutput"><span class="identifier">r</span></code>'s synthesized 397 attribute. Semantic actions, if present, may not change the 398 attribute's type. 399 </p> 400 </td> 401</tr> 402<tr> 403<td> 404 <p> 405 <code class="computeroutput"><span class="identifier">r</span><span class="special">.</span><span class="identifier">name</span><span class="special">()</span></code> 406 </p> 407 </td> 408<td> 409 <p> 410 Retrieve the current name of the rule object. 411 </p> 412 </td> 413</tr> 414<tr> 415<td> 416 <p> 417 <code class="computeroutput"><span class="identifier">r</span><span class="special">.</span><span class="identifier">name</span><span class="special">(</span><span class="identifier">name</span><span class="special">)</span></code> 418 </p> 419 </td> 420<td> 421 <p> 422 Set the current name of the rule object to be <code class="computeroutput"><span class="identifier">name</span></code>. 423 </p> 424 </td> 425</tr> 426</tbody> 427</table></div> 428<h6> 429<a name="spirit.qi.reference.nonterminal.rule.h7"></a> 430 <span class="phrase"><a name="spirit.qi.reference.nonterminal.rule.attributes"></a></span><a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.attributes">Attributes</a> 431 </h6> 432<div class="blockquote"><blockquote class="blockquote"><p> 433 The parser attribute of the rule is <code class="computeroutput"><span class="identifier">T</span></code>, 434 its synthesized attribute. See <a class="link" href="../parser_concepts/nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.attributes"><code class="computeroutput"><span class="identifier">Attribute</span></code></a> 435 </p></blockquote></div> 436<h6> 437<a name="spirit.qi.reference.nonterminal.rule.h8"></a> 438 <span class="phrase"><a name="spirit.qi.reference.nonterminal.rule.complexity"></a></span><a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.complexity">Complexity</a> 439 </h6> 440<div class="blockquote"><blockquote class="blockquote"><p> 441 The complexity is defined by the complexity of the RHS parser, <code class="computeroutput"><span class="identifier">p</span></code> 442 </p></blockquote></div> 443<h6> 444<a name="spirit.qi.reference.nonterminal.rule.h9"></a> 445 <span class="phrase"><a name="spirit.qi.reference.nonterminal.rule.example"></a></span><a class="link" href="rule.html#spirit.qi.reference.nonterminal.rule.example">Example</a> 446 </h6> 447<div class="note"><table border="0" summary="Note"> 448<tr> 449<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 450<th align="left">Note</th> 451</tr> 452<tr><td align="left" valign="top"><p> 453 The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.qi.reference.basics.examples">Basics Examples</a> 454 section. 455 </p></td></tr> 456</table></div> 457<p> 458 Some using declarations: 459 </p> 460<p> 461</p> 462<pre class="programlisting"><span class="keyword">using</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><span class="identifier">rule</span><span class="special">;</span> 463<span class="keyword">using</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><span class="identifier">int_</span><span class="special">;</span> 464<span class="keyword">using</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><span class="identifier">locals</span><span class="special">;</span> 465<span class="keyword">using</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><span class="identifier">_1</span><span class="special">;</span> 466<span class="keyword">using</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><span class="identifier">_a</span><span class="special">;</span> 467<span class="keyword">using</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><span class="identifier">alpha</span><span class="special">;</span> 468<span class="keyword">using</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><span class="identifier">char_</span><span class="special">;</span> 469<span class="keyword">using</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><span class="identifier">space_type</span><span class="special">;</span> 470</pre> 471<p> 472 </p> 473<p> 474 Basic rule: 475 </p> 476<p> 477</p> 478<pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*></span> <span class="identifier">r</span><span class="special">;</span> 479<span class="identifier">r</span> <span class="special">=</span> <span class="identifier">int_</span><span class="special">;</span> 480<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"123"</span><span class="special">,</span> <span class="identifier">r</span><span class="special">);</span> 481</pre> 482<p> 483 </p> 484<p> 485 Rule with synthesized attribute: 486 </p> 487<p> 488</p> 489<pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="keyword">int</span><span class="special">()></span> <span class="identifier">ra</span><span class="special">;</span> 490<span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">int_</span><span class="special">;</span> 491<span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span> 492<span class="identifier">test_parser_attr</span><span class="special">(</span><span class="string">"123"</span><span class="special">,</span> <span class="identifier">ra</span><span class="special">,</span> <span class="identifier">i</span><span class="special">);</span> 493<span class="identifier">assert</span><span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">123</span><span class="special">);</span> 494</pre> 495<p> 496 </p> 497<p> 498 Rule with skipper and synthesized attribute: 499 </p> 500<p> 501</p> 502<pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(),</span> <span class="identifier">space_type</span><span class="special">></span> <span class="identifier">rs</span><span class="special">;</span> 503<span class="identifier">rs</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">int_</span><span class="special">;</span> 504<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">v</span><span class="special">;</span> 505<span class="identifier">test_phrase_parser_attr</span><span class="special">(</span><span class="string">"123 456 789"</span><span class="special">,</span> <span class="identifier">rs</span><span class="special">,</span> <span class="identifier">v</span><span class="special">);</span> 506<span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">==</span> <span class="number">123</span><span class="special">);</span> 507<span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">==</span> <span class="number">456</span><span class="special">);</span> 508<span class="identifier">assert</span><span class="special">(</span><span class="identifier">v</span><span class="special">[</span><span class="number">2</span><span class="special">]</span> <span class="special">==</span> <span class="number">789</span><span class="special">);</span> 509</pre> 510<p> 511 </p> 512<p> 513 Rule with one local variable: 514 </p> 515<p> 516</p> 517<pre class="programlisting"><span class="identifier">rule</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*,</span> <span class="identifier">locals</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="special">></span> <span class="identifier">rl</span><span class="special">;</span> 518<span class="identifier">rl</span> <span class="special">=</span> <span class="identifier">alpha</span><span class="special">[</span><span class="identifier">_a</span> <span class="special">=</span> <span class="identifier">_1</span><span class="special">]</span> <span class="special">>></span> <span class="identifier">char_</span><span class="special">(</span><span class="identifier">_a</span><span class="special">);</span> <span class="comment">// get two identical characters</span> 519<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"aa"</span><span class="special">,</span> <span class="identifier">rl</span><span class="special">);</span> <span class="comment">// pass</span> 520<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"ax"</span><span class="special">,</span> <span class="identifier">rl</span><span class="special">);</span> <span class="comment">// fail</span> 521</pre> 522<p> 523 </p> 524</div> 525<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 526<td align="left"></td> 527<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 528 Distributed under the Boost Software License, Version 1.0. (See accompanying 529 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>) 530 </p> 531</div></td> 532</tr></table> 533<hr> 534<div class="spirit-nav"> 535<a accesskey="p" href="../nonterminal.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../nonterminal.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="grammar.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 536</div> 537</body> 538</html> 539
