1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Nonterminal</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="../parser_concepts.html" title="Parser Concepts"> 9<link rel="prev" href="naryparser.html" title="NaryParser"> 10<link rel="next" href="../basics.html" title="Parser Basics"> 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="naryparser.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../parser_concepts.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="../basics.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.parser_concepts.nonterminal"></a><a class="link" href="nonterminal.html" title="Nonterminal">Nonterminal</a> 28</h5></div></div></div> 29<h6> 30<a name="spirit.qi.reference.parser_concepts.nonterminal.h0"></a> 31 <span class="phrase"><a name="spirit.qi.reference.parser_concepts.nonterminal.description"></a></span><a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.description">Description</a> 32 </h6> 33<p> 34 A Nonterminal is a symbol in a <a class="link" href="../../../abstracts/parsing_expression_grammar.html" title="Parsing Expression Grammar">Parsing 35 Expression Grammar</a> production that represents a grammar fragment. 36 Nonterminals may self reference to specify recursion. This is one of 37 the most important concepts and the reason behind the word "recursive" 38 in recursive descent parsing. 39 </p> 40<h6> 41<a name="spirit.qi.reference.parser_concepts.nonterminal.h1"></a> 42 <span class="phrase"><a name="spirit.qi.reference.parser_concepts.nonterminal.refinement_of"></a></span><a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.refinement_of">Refinement 43 of</a> 44 </h6> 45<div class="blockquote"><blockquote class="blockquote"><p> 46 <a class="link" href="parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a> 47 </p></blockquote></div> 48<h6> 49<a name="spirit.qi.reference.parser_concepts.nonterminal.h2"></a> 50 <span class="phrase"><a name="spirit.qi.reference.parser_concepts.nonterminal.signature"></a></span><a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.signature">Signature</a> 51 </h6> 52<p> 53 Nonterminals can have both synthesized and inherited attributes. The 54 Nonterminal's <span class="emphasis"><em>Signature</em></span> specifies both the synthesized 55 and inherited attributes. The specification uses the function declarator 56 syntax: 57 </p> 58<pre class="programlisting"><span class="identifier">RT</span><span class="special">(</span><span class="identifier">A0</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="special">...,</span> <span class="identifier">AN</span><span class="special">)</span> 59</pre> 60<p> 61 where <code class="computeroutput"><span class="identifier">RT</span></code> is the Nonterminal's 62 synthesized attribute and <code class="computeroutput"><span class="identifier">A0</span></code> 63 ... <code class="computeroutput"><span class="identifier">AN</span></code> are the Nonterminal's 64 inherited attributes. 65 </p> 66<p> 67 The default value is <code class="computeroutput"><span class="keyword">void</span><span class="special">()</span></code> (no synthesized and inherited attributes). 68 </p> 69<h6> 70<a name="spirit.qi.reference.parser_concepts.nonterminal.h3"></a> 71 <span class="phrase"><a name="spirit.qi.reference.parser_concepts.nonterminal.attributes"></a></span><a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.attributes">Attributes</a> 72 </h6> 73<p> 74 The Nonterminal models a C++ function. The Nonterminal's synthesized 75 attribute is analogous to the function return value and its inherited 76 attributes are analogous to function arguments. The inherited attributes 77 (arguments) can be passed in just like any <a class="link" href="../basics.html#spirit.qi.reference.basics.lazy_argument">Lazy 78 Argument</a>, e.g.: 79 </p> 80<pre class="programlisting"><span class="identifier">r</span><span class="special">(</span><span class="identifier">expr</span><span class="special">)</span> <span class="comment">// Evaluate expr at parse time and pass the result to the Nonterminal r</span> 81</pre> 82<h6> 83<a name="spirit.qi.reference.parser_concepts.nonterminal.h4"></a> 84 <span class="phrase"><a name="spirit.qi.reference.parser_concepts.nonterminal._code__phrase_role__identifier___val__phrase___code_"></a></span><a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal._code__phrase_role__identifier___val__phrase___code_"><code class="computeroutput"><span class="identifier">_val</span></code></a> 85 </h6> 86<p> 87 The <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">_val</span></code> placeholder can be used in <a href="../../../../../../../../libs/phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a> semantic 88 actions anywhere in the Nonterminal's definition. This <a href="../../../../../../../../libs/phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a> 89 placeholder refers to the Nonterminal's (synthesized) attribute. The 90 <code class="computeroutput"><span class="identifier">_val</span></code> placeholder acts 91 like a mutable reference to the Nonterminal's attribute. 92 </p> 93<div class="note"><table border="0" summary="Note"> 94<tr> 95<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 96<th align="left">Note</th> 97</tr> 98<tr><td align="left" valign="top"><p> 99 Starting with <a href="http://boost-spirit.com" target="_top">Spirit</a> V2.5 100 (distributed with Boost V1.47) the placeholder <code class="computeroutput"><span class="identifier">_val</span></code> 101 can be used in semantic actions attached to top level parser components 102 as well. See <a class="link" href="../parse_api.html" title="Parser API">The Parse 103 API</a> for more information. 104 </p></td></tr> 105</table></div> 106<h6> 107<a name="spirit.qi.reference.parser_concepts.nonterminal.h5"></a> 108 <span class="phrase"><a name="spirit.qi.reference.parser_concepts.nonterminal._code__phrase_role__identifier___r1__phrase___code_______code__phrase_role__identifier__r10__phrase___code_"></a></span><a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal._code__phrase_role__identifier___r1__phrase___code_______code__phrase_role__identifier__r10__phrase___code_"><code class="computeroutput"><span class="identifier">_r1</span></code> ... <code class="computeroutput"><span class="identifier">r10</span></code></a> 109 </h6> 110<p> 111 The <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_r1</span></code> ... <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">r10</span></code> 112 placeholders can be used in <a href="../../../../../../../../libs/phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a> 113 semantic actions anywhere in the Nonterminal's definition. These <a href="../../../../../../../../libs/phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a> placeholders 114 refer to the Nonterminal's inherited attributes. 115 </p> 116<h6> 117<a name="spirit.qi.reference.parser_concepts.nonterminal.h6"></a> 118 <span class="phrase"><a name="spirit.qi.reference.parser_concepts.nonterminal.locals"></a></span><a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.locals">Locals</a> 119 </h6> 120<p> 121 Nonterminals can have local variables that will be created on the stack 122 at parse time. A locals descriptor added to the Nonterminal declaration 123 will give the Nonterminal local variables: 124 </p> 125<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T1</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...,</span> <span class="keyword">typename</span> <span class="identifier">TN</span><span class="special">></span> 126<span class="keyword">struct</span> <span class="identifier">locals</span><span class="special">;</span> 127</pre> 128<p> 129 where <code class="computeroutput"><span class="identifier">T0</span></code> ... <code class="computeroutput"><span class="identifier">TN</span></code> are the types of local variables 130 accessible in your <a href="../../../../../../../../libs/phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a> 131 semantic actions using the placeholders: 132 </p> 133<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 134<li class="listitem"> 135 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_a</span></code> 136 </li> 137<li class="listitem"> 138 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_b</span></code> 139 </li> 140<li class="listitem"> 141 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_c</span></code> 142 </li> 143<li class="listitem"> 144 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_d</span></code> 145 </li> 146<li class="listitem"> 147 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_e</span></code> 148 </li> 149<li class="listitem"> 150 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_f</span></code> 151 </li> 152<li class="listitem"> 153 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_g</span></code> 154 </li> 155<li class="listitem"> 156 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_h</span></code> 157 </li> 158<li class="listitem"> 159 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_i</span></code> 160 </li> 161<li class="listitem"> 162 <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_j</span></code> 163 </li> 164</ul></div> 165<p> 166 which correspond to the Nonterminal's local variables <code class="computeroutput"><span class="identifier">T0</span></code> 167 ... <code class="computeroutput"><span class="identifier">T9</span></code>. 168 </p> 169<div class="variablelist"> 170<p class="title"><b>Notation</b></p> 171<dl class="variablelist"> 172<dt><span class="term"><code class="computeroutput"><span class="identifier">x</span></code></span></dt> 173<dd><p> 174 A Nonterminal 175 </p></dd> 176<dt><span class="term"><code class="computeroutput"><span class="identifier">X</span></code></span></dt> 177<dd><p> 178 A Nonterminal type 179 </p></dd> 180<dt><span class="term"><code class="computeroutput"><span class="identifier">arg1</span></code>, <code class="computeroutput"><span class="identifier">arg2</span></code>, ..., <code class="computeroutput"><span class="identifier">argN</span></code></span></dt> 181<dd><p> 182 <a class="link" href="../basics.html#spirit.qi.reference.basics.lazy_argument">Lazy Arguments</a> 183 that evaluate to each of the Nonterminal's inherited attributes. 184 </p></dd> 185</dl> 186</div> 187<h6> 188<a name="spirit.qi.reference.parser_concepts.nonterminal.h7"></a> 189 <span class="phrase"><a name="spirit.qi.reference.parser_concepts.nonterminal.valid_expressions"></a></span><a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.valid_expressions">Valid 190 Expressions</a> 191 </h6> 192<p> 193 In addition to the requirements defined in <a class="link" href="parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a>, for any Nonterminal 194 the following must be met: 195 </p> 196<div class="informaltable"><table class="table"> 197<colgroup> 198<col> 199<col> 200<col> 201</colgroup> 202<thead><tr> 203<th> 204 <p> 205 Expression 206 </p> 207 </th> 208<th> 209 <p> 210 Semantics 211 </p> 212 </th> 213<th> 214 <p> 215 Return type 216 </p> 217 </th> 218</tr></thead> 219<tbody> 220<tr> 221<td> 222 <p> 223 <code class="computeroutput"><span class="identifier">x</span></code> 224 </p> 225 </td> 226<td> 227 <p> 228 In a parser expression, invoke Nonterminal <code class="computeroutput"><span class="identifier">x</span></code> 229 </p> 230 </td> 231<td> 232 <p> 233 <code class="computeroutput"><span class="identifier">X</span></code> 234 </p> 235 </td> 236</tr> 237<tr> 238<td> 239 <p> 240 <code class="computeroutput"><span class="identifier">x</span><span class="special">(</span><span class="identifier">arg1</span><span class="special">,</span> 241 <span class="identifier">arg2</span><span class="special">,</span> 242 <span class="special">...,</span> <span class="identifier">argN</span><span class="special">)</span></code> 243 </p> 244 </td> 245<td> 246 <p> 247 In a parser expression, invoke Nonterminal <code class="computeroutput"><span class="identifier">r</span></code> 248 passing in inherited attributes <code class="computeroutput"><span class="identifier">arg1</span></code> 249 ... <code class="computeroutput"><span class="identifier">argN</span></code> 250 </p> 251 </td> 252<td> 253 <p> 254 <code class="computeroutput"><span class="identifier">X</span></code> 255 </p> 256 </td> 257</tr> 258<tr> 259<td> 260 <p> 261 <code class="computeroutput"><span class="identifier">x</span><span class="special">.</span><span class="identifier">name</span><span class="special">(</span><span class="identifier">name</span><span class="special">)</span></code> 262 </p> 263 </td> 264<td> 265 <p> 266 Naming a Nonterminal. 267 </p> 268 </td> 269<td> 270 <p> 271 <code class="computeroutput"><span class="keyword">void</span></code> 272 </p> 273 </td> 274</tr> 275<tr> 276<td> 277 <p> 278 <code class="computeroutput"><span class="identifier">x</span><span class="special">.</span><span class="identifier">name</span><span class="special">()</span></code> 279 </p> 280 </td> 281<td> 282 <p> 283 Getting the name of a Nonterminal. 284 </p> 285 </td> 286<td> 287 <p> 288 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> 289 </p> 290 </td> 291</tr> 292<tr> 293<td> 294 <p> 295 debug(x) 296 </p> 297 </td> 298<td> 299 <p> 300 Debug Nonterminal <code class="computeroutput"><span class="identifier">x</span></code>. 301 </p> 302 </td> 303<td> 304 <p> 305 <code class="computeroutput"><span class="keyword">void</span></code> 306 </p> 307 </td> 308</tr> 309</tbody> 310</table></div> 311<h6> 312<a name="spirit.qi.reference.parser_concepts.nonterminal.h8"></a> 313 <span class="phrase"><a name="spirit.qi.reference.parser_concepts.nonterminal.type_expressions"></a></span><a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.type_expressions">Type 314 Expressions</a> 315 </h6> 316<div class="informaltable"><table class="table"> 317<colgroup> 318<col> 319<col> 320</colgroup> 321<thead><tr> 322<th> 323 <p> 324 Expression 325 </p> 326 </th> 327<th> 328 <p> 329 Description 330 </p> 331 </th> 332</tr></thead> 333<tbody> 334<tr> 335<td> 336 <p> 337 <code class="computeroutput"><span class="identifier">X</span><span class="special">::</span><span class="identifier">sig_type</span></code> 338 </p> 339 </td> 340<td> 341 <p> 342 The Signature of <code class="computeroutput"><span class="identifier">X</span></code>: 343 In a function signature form as described above in the Signature 344 paragraph. 345 </p> 346 </td> 347</tr> 348<tr> 349<td> 350 <p> 351 <code class="computeroutput"><span class="identifier">X</span><span class="special">::</span><span class="identifier">locals_type</span></code> 352 </p> 353 </td> 354<td> 355 <p> 356 The local variables of <code class="computeroutput"><span class="identifier">X</span></code>: 357 An <a href="../../../../../../../../libs/mpl/doc/refmanual/forward-sequence.html" target="_top">MPL 358 Forward Sequence</a>. 359 </p> 360 </td> 361</tr> 362</tbody> 363</table></div> 364<h6> 365<a name="spirit.qi.reference.parser_concepts.nonterminal.h9"></a> 366 <span class="phrase"><a name="spirit.qi.reference.parser_concepts.nonterminal.models"></a></span><a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.models">Models</a> 367 </h6> 368<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 369<li class="listitem"> 370 <a class="link" href="../nonterminal/rule.html" title="Parser Rule">rule</a> 371 </li> 372<li class="listitem"> 373 <a class="link" href="../nonterminal/grammar.html" title="Parser Grammar">grammar</a> 374 </li> 375</ul></div> 376</div> 377<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 378<td align="left"></td> 379<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 380 Distributed under the Boost Software License, Version 1.0. (See accompanying 381 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>) 382 </p> 383</div></td> 384</tr></table> 385<hr> 386<div class="spirit-nav"> 387<a accesskey="p" href="naryparser.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../parser_concepts.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="../basics.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 388</div> 389</body> 390</html> 391
