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| 2 | <head> | |
| 3 | <title>Parametric Parsers</title> | |
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| 9 | <table width="100%" border="0" background="theme/bkd2.gif" cellspacing="2"> | |
| 10 | <tr> | |
| 11 | <td width="10"> | |
| 12 | </td> | |
| 13 | <td width="85%"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Parametric | |
| 14 | Parsers</b></font> </td> | |
| 15 | <td width="112"><a href="http://spirit.sf.net"><img src="theme/spirit.gif" width="112" height="48" align="right" border="0"></a></td> | |
| 16 | </tr> | |
| 17 | </table> | |
| 18 | <br> | |
| 19 | <table border="0"> | |
| 20 | <tr> | |
| 21 | <td width="10"></td> | |
| 22 | <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> | |
| 23 | <td width="30"><a href="predefined_actors.html"><img src="theme/l_arr.gif" border="0"></a></td> | |
| 24 | <td width="30"><a href="functional.html"><img src="theme/r_arr.gif" border="0"></a></td> | |
| 25 | </tr> | |
| 26 | </table> | |
| 27 | <p>We already have a hint of the dynamic nature of the Spirit framework. This | |
| 28 | capability is fundamental to Spirit. Dynamic parsing is a very powerful concept. | |
| 29 | We shall take this concept further through run-time parametric parsers. We are | |
| 30 | able to handle parsing tasks that are impossible to do with any EBNF syntax | |
| 31 | alone.</p> | |
| 32 | <h2>A Little Secret</h2> | |
| 33 | <p> A little critter called <tt>boost::ref</tt> lurking in the boost distribution | |
| 34 | is quite powerful beast when used with Spirit's primitive parsers. We are used | |
| 35 | to seeing the Spirit primitive parsers created with string or character literals | |
| 36 | such as:</p> | |
| 37 | <pre> | |
| 38 | <code><span class=identifier>ch_p</span><span class=special>(</span><span class=literal>'A'</span><span class=special>) | |
| 39 | </span><span class=identifier>range_p</span><span class=special>(</span><span class=literal>'A'</span><span class=special>, </span><span class=literal>'Z'</span><span class=special>) | |
| 40 | </span><span class=identifier>str_p</span><span class=special>(</span><span class=string>"Hello World"</span><span class=special>)</span></code></pre> | |
| 41 | <p> str_p has a second form that accepts two iterators over the string:</p> | |
| 42 | <pre> | |
| 43 | <code><span class=keyword>char </span><span class=keyword>const</span><span class=special>* </span><span class=identifier>first </span><span class=special>= </span><span class=string>"My oh my"</span><span class=special>; | |
| 44 | </span><span class=keyword>char </span><span class=keyword>const</span><span class=special>* </span><span class=identifier>last </span><span class=special>= </span><span class=identifier>first </span><span class=special>+ </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>strlen</span><span class=special>(</span><span class=identifier>first</span><span class=special>); | |
| 45 | ||
| 46 | </span><span class=identifier>str_p</span><span class=special>(</span><span class=identifier>first</span><span class=special>, </span><span class=identifier>last</span><span class=special>)</span></code></pre> | |
| 47 | <p> What is not obvious is that we can use <tt>boost::ref</tt> as well:</p> | |
| 48 | <pre> | |
| 49 | <code><span class=keyword>char </span><span class=identifier>ch </span><span class=special>= </span><span class=literal>'A'</span><span class=special>; | |
| 50 | </span><span class=keyword>char </span><span class=identifier>from </span><span class=special>= </span><span class=literal>'A'</span><span class=special>; | |
| 51 | </span><span class=keyword>char </span><span class=identifier>to </span><span class=special>= </span><span class=literal>'Z'</span><span class=special>; | |
| 52 | ||
| 53 | </span><span class=identifier>ch_p</span><span class=special>(</span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>ref</span><span class=special>(</span><span class=identifier>ch</span><span class=special>)) | |
| 54 | </span><span class=identifier>range_p</span><span class=special>(</span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>ref</span><span class=special>(</span><span class=identifier>from</span><span class=special>), </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>ref</span><span class=special>(</span><span class=identifier>to</span><span class=special>))</span></code></pre> | |
| 55 | <p> When <tt>boost::ref</tt> is used, the actual parameters to <tt>ch_p</tt> and | |
| 56 | <tt>range_p</tt> are held by reference. This means that we can change the values | |
| 57 | of <tt>ch</tt>, <tt>from</tt> and <tt>to</tt> anytime and the corresponding | |
| 58 | <tt>ch_p</tt> and <tt>range_p</tt> parser will follow their dynamic values. | |
| 59 | Of course, since they are held by reference, you must make sure that the referenced | |
| 60 | object is not destructed while parsing.</p> | |
| 61 | <p> What about <tt>str_p</tt>?</p> | |
| 62 | <p> While the first form of <tt>str_p</tt> (the single argument form) is reserved | |
| 63 | for null terminated string constants, the second form (the two argument first/last | |
| 64 | iterator form) may be used:</p> | |
| 65 | <pre> | |
| 66 | <code><span class=keyword>char </span><span class=keyword>const</span><span class=special>* </span><span class=identifier>first </span><span class=special>= </span><span class=string>"My oh my"</span><span class=special>; | |
| 67 | </span><span class=keyword>char </span><span class=keyword>const</span><span class=special>* </span><span class=identifier>last </span><span class=special>= </span><span class=identifier>first </span><span class=special>+ </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>strlen</span><span class=special>(</span><span class=identifier>first</span><span class=special>); | |
| 68 | ||
| 69 | </span><span class=identifier>str_p</span><span class=special>(</span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>ref</span><span class=special>(</span><span class=identifier>first</span><span class=special>), </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>ref</span><span class=special>(</span><span class=identifier>last</span><span class=special>))</span></code></pre> | |
| 70 | <table width="80%" border="0" align="center"> | |
| 71 | <tr> | |
| 72 | <td class="note_box"> <img src="theme/note.gif" width="16" height="16"> Hey, | |
| 73 | don't forget <tt>chseq_p</tt>. All these apply to this seldom used primitive | |
| 74 | as well. </td> | |
| 75 | </tr> | |
| 76 | </table> | |
| 77 | <h2>Functional Parametric Primitives</h2> | |
| 78 | <pre> <span class="preprocessor">#include</span> <span class="special"><</span>boost<span class="special">/</span>spirit<span class="special">/</span>attribute<span class="special">/</span><span class="identifier">parametric</span><span class="special">.</span>hpp<span class="special">></span></pre> | |
| 79 | <p> Taking this further, Spirit includes functional versions of the primitives. | |
| 80 | Rather than taking in characters, strings or references to characters and strings | |
| 81 | (using boost::ref), the functional versions take in functions or functors.</p> | |
| 82 | <h3>f_chlit and f_ch_p</h3> | |
| 83 | <p> The functional version of <tt>chlit</tt>. This parser takes in a function | |
| 84 | or functor (function object). The function is expected to have an interface | |
| 85 | compatible with:</p> | |
| 86 | <pre> | |
| 87 | <code><span class=identifier>CharT </span><span class=identifier>func</span><span class=special>()</span></code></pre> | |
| 88 | <p> where CharT is the character type (e.g. <tt>char</tt>, <tt>int</tt>, <tt>wchar_t</tt>).</p> | |
| 89 | <p> The functor is expected to have an interface compatible with:</p> | |
| 90 | <pre> | |
| 91 | <code><span class=keyword>struct </span><span class=identifier>functor | |
| 92 | </span><span class=special>{ | |
| 93 | </span><span class=identifier>CharT </span><span class=keyword>operator</span><span class=special>()() </span><span class=keyword>const</span><span class=special>; | |
| 94 | </span><span class=special>};</span></code></pre> | |
| 95 | <p> where CharT is the character type (e.g. <tt>char</tt>, <tt>int</tt>, <tt>wchar_t</tt>).</p> | |
| 96 | <p> Here's a contrived example:</p> | |
| 97 | <pre> | |
| 98 | <code><span class=keyword>struct </span><span class=identifier>X | |
| 99 | </span><span class=special>{ | |
| 100 | </span><span class=keyword>char </span><span class=keyword>operator</span><span class=special>()() </span><span class=keyword>const | |
| 101 | </span><span class=special>{ | |
| 102 | </span><span class=keyword>return </span><span class=literal>'X'</span><span class=special>; </span><span class=special> | |
| 103 | } | |
| 104 | </span><span class=special>};</span></code></pre> | |
| 105 | <p> Now we can use X to create our f_chlit parser:</p> | |
| 106 | <pre> | |
| 107 | <code><span class=identifier>f_ch_p</span><span class=special>(</span><span class=identifier>X</span><span class=special>())</span></code></pre> | |
| 108 | <h3>f_range and f_range_p</h3> | |
| 109 | <p> The functional version of <tt>range</tt>. This parser takes in a function | |
| 110 | or functor compatible with the interfaces above. The difference is that <tt>f_range</tt> | |
| 111 | (and <tt>f_range_p</tt>) expects two functors. One for the start and one for | |
| 112 | the end of the range.</p> | |
| 113 | <h3>f_chseq and f_chseq_p</h3> | |
| 114 | <p> The functional version of <tt>chseq</tt>. This parser takes in two functions | |
| 115 | or functors. One for the begin iterator and one for the end iterator. The function | |
| 116 | is expected to have an interface compatible with:</p> | |
| 117 | <pre> | |
| 118 | <code><span class=identifier>IteratorT </span><span class=identifier>func</span><span class=special>()</span></code></pre> | |
| 119 | <p> where <tt>IteratorT</tt> is the iterator type (e.g. <tt>char const*</tt>, | |
| 120 | <tt>wchar_t const*</tt>).</p> | |
| 121 | <p> The functor is expected to have an interface compatible with:</p> | |
| 122 | <pre> | |
| 123 | <code><span class=keyword>struct </span><span class=identifier>functor | |
| 124 | </span><span class=special>{ | |
| 125 | </span><span class=identifier>IteratorT </span><span class=keyword>operator</span><span class=special>()() </span><span class=keyword>const</span><span class=special>; | |
| 126 | </span><span class=special>};</span></code></pre> | |
| 127 | <p> where <tt>IteratorT</tt> is the iterator type (e.g. <tt>char const*</tt>, | |
| 128 | <tt>wchar_t const*</tt>).</p> | |
| 129 | <h3>f_strlit and f_str_p</h3> | |
| 130 | <p> The functional version of <tt>strlit</tt>. This parser takes in two functions | |
| 131 | or functors compatible with the interfaces that <tt>f_chseq</tt> expects.</p> | |
| 132 | <table border="0"> | |
| 133 | <tr> | |
| 134 | <td width="10"></td> | |
| 135 | <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> | |
| 136 | <td width="30"><a href="predefined_actors.html"><img src="theme/l_arr.gif" border="0"></a></td> | |
| 137 | <td width="30"><a href="functional.html"><img src="theme/r_arr.gif" border="0"></a></td> | |
| 138 | </tr> | |
| 139 | </table> | |
| 140 | <br> | |
| 141 | <hr size="1"> | |
| 142 | <p class="copyright">Copyright © 1998-2003 Joel de Guzman<br> | |
| 143 | <br> | |
| 144 | <font size="2">Use, modification and distribution is subject to the Boost Software | |
| 145 | License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at | |
| 146 | http://www.boost.org/LICENSE_1_0.txt)</font></p> | |
| 147 | <p class="copyright"> </p> | |
| 148 | </body> | |
| 149 | </html> |