1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Sequential Or Parser (a || b)</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="../operator.html" title="Parser Operators"> 9<link rel="prev" href="sequence.html" title="Sequence Parser (a >> b)"> 10<link rel="next" href="../stream.html" title="Stream Parsers"> 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="sequence.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.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="../stream.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.operator.sequential_or"></a><a class="link" href="sequential_or.html" title="Sequential Or Parser (a || b)">Sequential 28 Or Parser (<code class="computeroutput"><span class="identifier">a</span> <span class="special">||</span> 29 <span class="identifier">b</span></code>)</a> 30</h5></div></div></div> 31<h6> 32<a name="spirit.qi.reference.operator.sequential_or.h0"></a> 33 <span class="phrase"><a name="spirit.qi.reference.operator.sequential_or.description"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.description">Description</a> 34 </h6> 35<p> 36 The sequential-or operator, <code class="computeroutput"><span class="identifier">a</span> 37 <span class="special">||</span> <span class="identifier">b</span></code>, 38 matches <code class="computeroutput"><span class="identifier">a</span></code> or <code class="computeroutput"><span class="identifier">b</span></code> or <code class="computeroutput"><span class="identifier">a</span></code> 39 followed by <code class="computeroutput"><span class="identifier">b</span></code>. That is, 40 if both <code class="computeroutput"><span class="identifier">a</span></code> and <code class="computeroutput"><span class="identifier">b</span></code> match, it must be in sequence; this 41 is equivalent to <code class="computeroutput"><span class="identifier">a</span> <span class="special">>></span> 42 <span class="special">-</span><span class="identifier">b</span> 43 <span class="special">|</span> <span class="identifier">b</span></code>: 44 </p> 45<pre class="programlisting"><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span> <span class="special">||</span> <span class="special">...</span> 46</pre> 47<h6> 48<a name="spirit.qi.reference.operator.sequential_or.h1"></a> 49 <span class="phrase"><a name="spirit.qi.reference.operator.sequential_or.header"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.header">Header</a> 50 </h6> 51<pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/operator/sequential_or.hpp></span> 52<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_sequential_or</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 53</pre> 54<p> 55 Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>. 56 </p> 57<h6> 58<a name="spirit.qi.reference.operator.sequential_or.h2"></a> 59 <span class="phrase"><a name="spirit.qi.reference.operator.sequential_or.model_of"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.model_of">Model of</a> 60 </h6> 61<div class="blockquote"><blockquote class="blockquote"><p> 62 <a class="link" href="../parser_concepts/naryparser.html" title="NaryParser"><code class="computeroutput"><span class="identifier">NaryParser</span></code></a> 63 </p></blockquote></div> 64<div class="variablelist"> 65<p class="title"><b>Notation</b></p> 66<dl class="variablelist"> 67<dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code>, <code class="computeroutput"><span class="identifier">b</span></code></span></dt> 68<dd><p> 69 A <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a> 70 </p></dd> 71</dl> 72</div> 73<h6> 74<a name="spirit.qi.reference.operator.sequential_or.h3"></a> 75 <span class="phrase"><a name="spirit.qi.reference.operator.sequential_or.expression_semantics"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.expression_semantics">Expression 76 Semantics</a> 77 </h6> 78<p> 79 Semantics of an expression is defined only where it differs from, or 80 is not defined in <a class="link" href="../parser_concepts/naryparser.html" title="NaryParser"><code class="computeroutput"><span class="identifier">NaryParser</span></code></a>. 81 </p> 82<div class="informaltable"><table class="table"> 83<colgroup> 84<col> 85<col> 86</colgroup> 87<thead><tr> 88<th> 89 <p> 90 Expression 91 </p> 92 </th> 93<th> 94 <p> 95 Semantics 96 </p> 97 </th> 98</tr></thead> 99<tbody><tr> 100<td> 101 <p> 102 <code class="computeroutput"><span class="identifier">a</span> <span class="special">||</span> 103 <span class="identifier">b</span></code> 104 </p> 105 </td> 106<td> 107 <p> 108 Match <code class="computeroutput"><span class="identifier">a</span></code> or 109 <code class="computeroutput"><span class="identifier">b</span></code> in sequence. 110 equivalent to <code class="computeroutput"><span class="identifier">a</span> <span class="special">>></span> <span class="special">-</span><span class="identifier">b</span> <span class="special">|</span> 111 <span class="identifier">b</span></code> 112 </p> 113 </td> 114</tr></tbody> 115</table></div> 116<h6> 117<a name="spirit.qi.reference.operator.sequential_or.h4"></a> 118 <span class="phrase"><a name="spirit.qi.reference.operator.sequential_or.attributes"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.attributes">Attributes</a> 119 </h6> 120<p> 121 See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.qi.quick_reference.compound_attribute_rules.notation">Compound 122 Attribute Notation</a>. 123 </p> 124<div class="informaltable"><table class="table"> 125<colgroup> 126<col> 127<col> 128</colgroup> 129<thead><tr> 130<th> 131 <p> 132 Expression 133 </p> 134 </th> 135<th> 136 <p> 137 Attribute 138 </p> 139 </th> 140</tr></thead> 141<tbody><tr> 142<td> 143 <p> 144 <code class="computeroutput"><span class="identifier">a</span> <span class="special">||</span> 145 <span class="identifier">b</span></code> 146 </p> 147 </td> 148<td> 149 <p> 150</p> 151<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">tuple</span><span class="special"><</span><span class="identifier">optional</span><span class="special"><</span><span class="identifier">A</span><span class="special">>,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">B</span><span class="special">></span> <span class="special">></span> 152<span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span> 153<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">B</span><span class="special">></span> 154<span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">Unused</span> 155 156<span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--></span> <span class="special">(</span><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">vector</span><span class="special"><</span><span class="identifier">optional</span><span class="special"><</span><span class="identifier">A</span><span class="special">></span> <span class="special">></span></pre> 157<p> 158 </p> 159 </td> 160</tr></tbody> 161</table></div> 162<div class="note"><table border="0" summary="Note"> 163<tr> 164<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 165<th align="left">Note</th> 166</tr> 167<tr><td align="left" valign="top"> 168<p> 169 The sequential-or parser behaves attribute-wise very similar to the 170 plain sequence parser (<code class="computeroutput"><span class="identifier">a</span> 171 <span class="special">>></span> <span class="identifier">b</span></code>) 172 in the sense that it exposes the attributes of its elements separately. 173 For instance, if you attach a semantic action to the whole sequential-or: 174</p> 175<pre class="programlisting"><span class="special">(</span><span class="identifier">int_</span> <span class="special">||</span> <span class="identifier">int_</span><span class="special">)[</span><span class="identifier">print_pair</span><span class="special">(</span><span class="identifier">_1</span><span class="special">,</span> <span class="identifier">_2</span><span class="special">)]</span> 176</pre> 177<p> 178 the function object <code class="computeroutput"><span class="identifier">print_pair</span></code> 179 would be invoked with the attribute of the first <code class="computeroutput"><span class="identifier">int_</span></code> 180 (<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code>) 181 as its first parameter and the attribute of the second <code class="computeroutput"><span class="identifier">int_</span></code> (<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code> as well) as its second parameter. 182 </p> 183</td></tr> 184</table></div> 185<h6> 186<a name="spirit.qi.reference.operator.sequential_or.h5"></a> 187 <span class="phrase"><a name="spirit.qi.reference.operator.sequential_or.complexity"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.complexity">Complexity</a> 188 </h6> 189<div class="blockquote"><blockquote class="blockquote"><p> 190 The overall complexity of the sequential-or parser is defined by the 191 sum of the complexities of its elements. The complexity of the sequential-or 192 itself is O(N), where N is the number of elements in the sequence. 193 </p></blockquote></div> 194<h6> 195<a name="spirit.qi.reference.operator.sequential_or.h6"></a> 196 <span class="phrase"><a name="spirit.qi.reference.operator.sequential_or.example"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.example">Example</a> 197 </h6> 198<div class="note"><table border="0" summary="Note"> 199<tr> 200<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> 201<th align="left">Note</th> 202</tr> 203<tr><td align="left" valign="top"><p> 204 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> 205 section. 206 </p></td></tr> 207</table></div> 208<p> 209 Some using declarations: 210 </p> 211<p> 212</p> 213<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">int_</span><span class="special">;</span> 214</pre> 215<p> 216 </p> 217<p> 218 Correctly parsing a number with optional fractional digits: 219 </p> 220<p> 221</p> 222<pre class="programlisting"><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"123.456"</span><span class="special">,</span> <span class="identifier">int_</span> <span class="special">||</span> <span class="special">(</span><span class="char">'.'</span> <span class="special">>></span> <span class="identifier">int_</span><span class="special">));</span> <span class="comment">// full</span> 223<span class="identifier">test_parser</span><span class="special">(</span><span class="string">"123"</span><span class="special">,</span> <span class="identifier">int_</span> <span class="special">||</span> <span class="special">(</span><span class="char">'.'</span> <span class="special">>></span> <span class="identifier">int_</span><span class="special">));</span> <span class="comment">// just the whole number</span> 224<span class="identifier">test_parser</span><span class="special">(</span><span class="string">".456"</span><span class="special">,</span> <span class="identifier">int_</span> <span class="special">||</span> <span class="special">(</span><span class="char">'.'</span> <span class="special">>></span> <span class="identifier">int_</span><span class="special">));</span> <span class="comment">// just the fraction</span> 225</pre> 226<p> 227 </p> 228<p> 229 A naive but incorrect solution would try to do this using optionals (e.g.): 230 </p> 231<pre class="programlisting"><span class="identifier">int_</span> <span class="special">>></span> <span class="special">-(</span><span class="char">'.'</span> <span class="special">>></span> <span class="identifier">int_</span><span class="special">)</span> <span class="comment">// will not match ".456"</span> 232<span class="special">-</span><span class="identifier">int_</span> <span class="special">>></span> <span class="special">(</span><span class="char">'.'</span> <span class="special">>></span> <span class="identifier">int_</span><span class="special">)</span> <span class="comment">// will not match "123"</span> 233<span class="special">-</span><span class="identifier">int_</span> <span class="special">>></span> <span class="special">-(</span><span class="char">'.'</span> <span class="special">>></span> <span class="identifier">int_</span><span class="special">)</span> <span class="comment">// will match empty strings! Ooops.</span> 234</pre> 235</div> 236<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 237<td align="left"></td> 238<td align="right"><div class="copyright-footer">Copyright © 2001-2011 Joel de Guzman, Hartmut Kaiser<p> 239 Distributed under the Boost Software License, Version 1.0. (See accompanying 240 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>) 241 </p> 242</div></td> 243</tr></table> 244<hr> 245<div class="spirit-nav"> 246<a accesskey="p" href="sequence.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.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="../stream.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 247</div> 248</body> 249</html> 250
