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  28 <div><h2 class="title">
  29 <a name="proto"></a>Chapter&#160;33.&#160;Boost.Proto</h2></div>
  30 <div><div class="author"><h3 class="author">
  31 <span class="firstname">Eric</span> <span class="surname">Niebler</span>
  32 </h3></div></div>
  33 <div><p class="copyright">Copyright &#169; 2008 Eric Niebler</p></div>
  34 <div><div class="legalnotice">
  35 <a name="proto.legal"></a><p>
  36         Distributed under the Boost Software License, Version 1.0. (See accompanying
  37         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>)
  38       </p>
  39 </div></div>
  40 </div></div>
  41 <div class="toc">
  42 <p><b>Table of Contents</b></p>
  43 <dl class="toc">
  44 <dt><span class="section"><a href="proto.html#boost_proto.preface">Preface</a></span></dt>
  45 <dt><span class="section"><a href="proto/users_guide.html">Users' Guide</a></span></dt>
  46 <dd><dl>
  47 <dt><span class="section"><a href="proto/users_guide.html#boost_proto.users_guide.getting_started">Getting Started</a></span></dt>
  48 <dt><span class="section"><a href="proto/users_guide.html#boost_proto.users_guide.front_end">Fronts Ends: Defining
  49       Terminals and Non-Terminals of Your EDSL</a></span></dt>
  50 <dt><span class="section"><a href="proto/users_guide.html#boost_proto.users_guide.intermediate_form">Intermediate
  51       Form: Understanding and Introspecting Expressions</a></span></dt>
  52 <dt><span class="section"><a href="proto/users_guide.html#boost_proto.users_guide.back_end">Back Ends: Making Expression
  53       Templates Do Useful Work</a></span></dt>
  54 <dt><span class="section"><a href="proto/users_guide.html#boost_proto.users_guide.examples">Examples</a></span></dt>
  55 <dt><span class="section"><a href="proto/users_guide.html#boost_proto.users_guide.resources">Background and Resources</a></span></dt>
  56 <dt><span class="section"><a href="proto/users_guide.html#boost_proto.users_guide.glossary">Glossary</a></span></dt>
  57 </dl></dd>
  58 <dt><span class="section"><a href="proto/reference.html">Reference</a></span></dt>
  59 <dd><dl>
  60 <dt><span class="section"><a href="proto/reference.html#proto.concepts">Concepts</a></span></dt>
  61 <dt><span class="section"><a href="proto/reference.html#proto.reference.classes">Classes</a></span></dt>
  62 <dt><span class="section"><a href="proto/reference.html#proto.reference.functions">Functions</a></span></dt>
  63 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.args_hpp">Header &lt;boost/proto/args.hpp&gt;</a></span></dt>
  64 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.core_hpp">Header &lt;boost/proto/core.hpp&gt;</a></span></dt>
  65 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.debug_hpp">Header &lt;boost/proto/debug.hpp&gt;</a></span></dt>
  66 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.deep_copy_hpp">Header &lt;boost/proto/deep_copy.hpp&gt;</a></span></dt>
  67 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.domain_hpp">Header &lt;boost/proto/domain.hpp&gt;</a></span></dt>
  68 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.eval_hpp">Header &lt;boost/proto/eval.hpp&gt;</a></span></dt>
  69 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.expr_hpp">Header &lt;boost/proto/expr.hpp&gt;</a></span></dt>
  70 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.extends_hpp">Header &lt;boost/proto/extends.hpp&gt;</a></span></dt>
  71 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional_hpp">Header &lt;boost/proto/functional.hpp&gt;</a></span></dt>
  72 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.fusion_hpp">Header &lt;boost/proto/functional/fusion.hpp&gt;</a></span></dt>
  73 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.fusion.at_hpp">Header &lt;boost/proto/functional/fusion/at.hpp&gt;</a></span></dt>
  74 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.fusion.pop_back_hpp">Header &lt;boost/proto/functional/fusion/pop_back.hpp&gt;</a></span></dt>
  75 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.fusion.pop_front_hpp">Header &lt;boost/proto/functional/fusion/pop_front.hpp&gt;</a></span></dt>
  76 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.fusion.push_back_hpp">Header &lt;boost/proto/functional/fusion/push_back.hpp&gt;</a></span></dt>
  77 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.fusion.push_front_hpp">Header &lt;boost/proto/functional/fusion/push_front.hpp&gt;</a></span></dt>
  78 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.fusion.reverse_hpp">Header &lt;boost/proto/functional/fusion/reverse.hpp&gt;</a></span></dt>
  79 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.range.begin_hpp">Header &lt;boost/proto/functional/range/begin.hpp&gt;</a></span></dt>
  80 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.range.empty_hpp">Header &lt;boost/proto/functional/range/empty.hpp&gt;</a></span></dt>
  81 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.range.end_hpp">Header &lt;boost/proto/functional/range/end.hpp&gt;</a></span></dt>
  82 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.range.rbegin_hpp">Header &lt;boost/proto/functional/range/rbegin.hpp&gt;</a></span></dt>
  83 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.range.rend_hpp">Header &lt;boost/proto/functional/range/rend.hpp&gt;</a></span></dt>
  84 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.range.size_hpp">Header &lt;boost/proto/functional/range/size.hpp&gt;</a></span></dt>
  85 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.std_hpp">Header &lt;boost/proto/functional/std.hpp&gt;</a></span></dt>
  86 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.std.iterator_hpp">Header &lt;boost/proto/functional/std/iterator.hpp&gt;</a></span></dt>
  87 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.functional.std.utility_hpp">Header &lt;boost/proto/functional/std/utility.hpp&gt;</a></span></dt>
  88 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.fusion_hpp">Header &lt;boost/proto/fusion.hpp&gt;</a></span></dt>
  89 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.generate_hpp">Header &lt;boost/proto/generate.hpp&gt;</a></span></dt>
  90 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.literal_hpp">Header &lt;boost/proto/literal.hpp&gt;</a></span></dt>
  91 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.make_expr_hpp">Header &lt;boost/proto/make_expr.hpp&gt;</a></span></dt>
  92 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.matches_hpp">Header &lt;boost/proto/matches.hpp&gt;</a></span></dt>
  93 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.operators_hpp">Header &lt;boost/proto/operators.hpp&gt;</a></span></dt>
  94 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.proto_hpp">Header &lt;boost/proto/proto.hpp&gt;</a></span></dt>
  95 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.proto_fwd_hpp">Header &lt;boost/proto/proto_fwd.hpp&gt;</a></span></dt>
  96 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.proto_typeof_hpp">Header &lt;boost/proto/proto_typeof.hpp&gt;</a></span></dt>
  97 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.repeat_hpp">Header &lt;boost/proto/repeat.hpp&gt;</a></span></dt>
  98 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.tags_hpp">Header &lt;boost/proto/tags.hpp&gt;</a></span></dt>
  99 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.traits_hpp">Header &lt;boost/proto/traits.hpp&gt;</a></span></dt>
 100 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform_hpp">Header &lt;boost/proto/transform.hpp&gt;</a></span></dt>
 101 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.arg_hpp">Header &lt;boost/proto/transform/arg.hpp&gt;</a></span></dt>
 102 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.call_hpp">Header &lt;boost/proto/transform/call.hpp&gt;</a></span></dt>
 103 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.default_hpp">Header &lt;boost/proto/transform/default.hpp&gt;</a></span></dt>
 104 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.env_hpp">Header &lt;boost/proto/transform/env.hpp&gt;</a></span></dt>
 105 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.fold_hpp">Header &lt;boost/proto/transform/fold.hpp&gt;</a></span></dt>
 106 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.fold_tree_hpp">Header &lt;boost/proto/transform/fold_tree.hpp&gt;</a></span></dt>
 107 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.impl_hpp">Header &lt;boost/proto/transform/impl.hpp&gt;</a></span></dt>
 108 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.integral_c_hpp">Header &lt;boost/proto/transform/integral_c.hpp&gt;</a></span></dt>
 109 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.lazy_hpp">Header &lt;boost/proto/transform/lazy.hpp&gt;</a></span></dt>
 110 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.make_hpp">Header &lt;boost/proto/transform/make.hpp&gt;</a></span></dt>
 111 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.pass_through_hpp">Header &lt;boost/proto/transform/pass_through.hpp&gt;</a></span></dt>
 112 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.transform.when_hpp">Header &lt;boost/proto/transform/when.hpp&gt;</a></span></dt>
 113 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.context_hpp">Header &lt;boost/proto/context.hpp&gt;</a></span></dt>
 114 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.context.callable_hpp">Header &lt;boost/proto/context/callable.hpp&gt;</a></span></dt>
 115 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.context.default_hpp">Header &lt;boost/proto/context/default.hpp&gt;</a></span></dt>
 116 <dt><span class="section"><a href="proto/reference.html#header.boost.proto.context.null_hpp">Header &lt;boost/proto/context/null.hpp&gt;</a></span></dt>
 117 </dl></dd>
 118 <dt><span class="section"><a href="proto/appendices.html">Appendices</a></span></dt>
 119 <dd><dl>
 120 <dt><span class="section"><a href="proto/appendices.html#boost_proto.appendices.release_notes">Appendix A: Release
 121       Notes</a></span></dt>
 122 <dt><span class="section"><a href="proto/appendices.html#boost_proto.appendices.history">Appendix B: History</a></span></dt>
 123 <dt><span class="section"><a href="proto/appendices.html#boost_proto.appendices.rationale">Appendix C: Rationale</a></span></dt>
 124 <dt><span class="section"><a href="proto/appendices.html#boost_proto.appendices.implementation">Appendix D: Implementation
 125       Notes</a></span></dt>
 126 <dt><span class="section"><a href="proto/appendices.html#boost_proto.appendices.acknowledgements">Appendix E:
 127       Acknowledgements</a></span></dt>
 128 </dl></dd>
 129 </dl>
 130 </div>
 131 <div class="section">
 132 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 133 <a name="boost_proto.preface"></a><a class="link" href="proto.html#boost_proto.preface" title="Preface">Preface</a>
 134 </h2></div></div></div>
 135 <div class="blockquote"><blockquote class="blockquote"><p>
 136         <span class="quote">&#8220;<span class="quote">There are more things in heaven and earth, Horatio, than are dreamt
 137         of in your philosophy.</span>&#8221;</span>
 138       </p></blockquote></div>
 139 <div class="blockquote"><blockquote class="blockquote"><p>
 140         <span class="bold"><strong><span class="emphasis"><em>-- William Shakespeare</em></span></strong></span>
 141       </p></blockquote></div>
 142 <h4>
 143 <a name="boost_proto.preface.h0"></a>
 144       <span class="phrase"><a name="boost_proto.preface.description"></a></span><a class="link" href="proto.html#boost_proto.preface.description">Description</a>
 145     </h4>
 146 <p>
 147       Proto is a framework for building Embedded Domain-Specific Languages in C++.
 148       It provides tools for constructing, type-checking, transforming and executing
 149       <span class="emphasis"><em>expression templates</em></span><a href="#ftn.boost_proto.preface.f0" class="footnote" name="boost_proto.preface.f0"><sup class="footnote">[33]</sup></a>. More specifically, Proto provides:
 150     </p>
 151 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 152 <li class="listitem">
 153           An expression tree data structure.
 154         </li>
 155 <li class="listitem">
 156           A mechanism for giving expressions additional behaviors and members.
 157         </li>
 158 <li class="listitem">
 159           Operator overloads for building the tree from an expression.
 160         </li>
 161 <li class="listitem">
 162           Utilities for defining the grammar to which an expression must conform.
 163         </li>
 164 <li class="listitem">
 165           An extensible mechanism for immediately executing an expression template.
 166         </li>
 167 <li class="listitem">
 168           An extensible set of tree transformations to apply to expression trees.
 169         </li>
 170 </ul></div>
 171 <h4>
 172 <a name="boost_proto.preface.h1"></a>
 173       <span class="phrase"><a name="boost_proto.preface.motivation"></a></span><a class="link" href="proto.html#boost_proto.preface.motivation">Motivation</a>
 174     </h4>
 175 <p>
 176       Expression Templates are an advanced technique that C++ library developers
 177       use to define embedded mini-languages that target specific problem domains.
 178       The technique has been used to create efficient and easy-to-use libraries for
 179       linear algebra as well as to define C++ parser generators with a readable syntax.
 180       But developing such a library involves writing an inordinate amount of unreadable
 181       and unmaintainable template mumbo-jumbo. Boost.Proto eases the development
 182       of <a class="link" href="proto/users_guide.html#boost_proto.users_guide.glossary.edsl">domain-specific embedded
 183       languages (EDSLs)</a>. Use Proto to define the primitives of your mini-language
 184       and let Proto handle the operator overloading and the construction of the expression
 185       parse tree. Immediately evaluate the expression tree by passing it a function
 186       object. Or transform the expression tree by defining the grammar of your mini-language,
 187       decorated with an assortment of tree transforms provided by Proto or defined
 188       by you. Then use the grammar to give your users short and readable syntax errors
 189       for invalid expressions! No more mumbo-jumbo -- an expression template library
 190       developed with Proto is declarative and readable.
 191     </p>
 192 <p>
 193       In short, Proto is an EDSL for defining EDSLs.
 194     </p>
 195 <h4>
 196 <a name="boost_proto.preface.h2"></a>
 197       <span class="phrase"><a name="boost_proto.preface.how_to_use_this_documentation"></a></span><a class="link" href="proto.html#boost_proto.preface.how_to_use_this_documentation">How
 198       to Use This Documentation</a>
 199     </h4>
 200 <p>
 201       This documentation makes use of the following naming and formatting conventions.
 202     </p>
 203 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 204 <li class="listitem">
 205           Code is in <code class="computeroutput"><span class="identifier">fixed</span> <span class="identifier">width</span>
 206           <span class="identifier">font</span></code> and is syntax-highlighted.
 207         </li>
 208 <li class="listitem">
 209           Replaceable text that you will need to supply is in <em class="replaceable"><code>italics</code></em>.
 210         </li>
 211 <li class="listitem">
 212           If a name refers to a free function, it is specified like this: <code class="computeroutput"><span class="identifier">free_function</span><span class="special">()</span></code>;
 213           that is, it is in code font and its name is followed by <code class="computeroutput"><span class="special">()</span></code>
 214           to indicate that it is a free function.
 215         </li>
 216 <li class="listitem">
 217           If a name refers to a class template, it is specified like this: <code class="computeroutput"><span class="identifier">class_template</span><span class="special">&lt;&gt;</span></code>;
 218           that is, it is in code font and its name is followed by <code class="computeroutput"><span class="special">&lt;&gt;</span></code>
 219           to indicate that it is a class template.
 220         </li>
 221 <li class="listitem">
 222           If a name refers to a function-like macro, it is specified like this:
 223           <code class="computeroutput"><span class="identifier">MACRO</span><span class="special">()</span></code>;
 224           that is, it is uppercase in code font and its name is followed by <code class="computeroutput"><span class="special">()</span></code> to indicate that it is a function-like
 225           macro. Object-like macros appear without the trailing <code class="computeroutput"><span class="special">()</span></code>.
 226         </li>
 227 <li class="listitem">
 228           Names that refer to <span class="emphasis"><em>concepts</em></span> in the generic programming
 229           sense are specified in CamelCase.
 230         </li>
 231 </ul></div>
 232 <div class="note"><table border="0" summary="Note">
 233 <tr>
 234 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../doc/src/images/note.png"></td>
 235 <th align="left">Note</th>
 236 </tr>
 237 <tr><td align="left" valign="top"><p>
 238         In addition, notes such as this one specify non-essential information that
 239         provides additional background or rationale.
 240       </p></td></tr>
 241 </table></div>
 242 <p>
 243       Finally, you can mentally add the following to any code fragments in this document:
 244     </p>
 245 <pre class="programlisting"><span class="comment">// Include all of Proto</span>
 246 <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">proto</span><span class="special">/</span><span class="identifier">proto</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
 247
 248 <span class="comment">// Create some namespace aliases</span>
 249 <span class="keyword">namespace</span> <span class="identifier">mpl</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">;</span>
 250 <span class="keyword">namespace</span> <span class="identifier">fusion</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">fusion</span><span class="special">;</span>
 251 <span class="keyword">namespace</span> <span class="identifier">proto</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">proto</span><span class="special">;</span>
 252
 253 <span class="comment">// Allow unqualified use of Proto's wildcard pattern</span>
 254 <span class="keyword">using</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">_</span><span class="special">;</span>
 255 </pre>
 256 </div>
 257 <div class="footnotes">
 258 <br><hr style="width:100; text-align:left;margin-left: 0">
 259 <div id="ftn.boost_proto.preface.f0" class="footnote"><p><a href="#boost_proto.preface.f0" class="para"><sup class="para">[33] </sup></a>
 260         See <a href="http://en.wikipedia.org/wiki/Expression_templates" target="_top">Expression
 261         Templates</a>
 262       </p></div>
 263 </div>
 264 </div>
 265 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 266 <td align="left"><p><small>Last revised: December 10, 2019 at 00:26:26 GMT</small></p></td>
 267 <td align="right"><div class="copyright-footer"></div></td>
 268 </tr></table>
 269 <hr>
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