townforge/spirit
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity
cc
spirit/classic/doc/primitives.html
Joel de Guzman a64194064f #3007 
[SVN r53423]
2009-05-30 02:16:54 +00:00

250 lines
21 KiB
HTML
Raw Permalink Blame History

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head>
<title>Primitives</title><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" href="theme/style.css" type="text/css"></head>
<body>
<table background="theme/bkd2.gif" border="0" cellspacing="2" width="100%">
<tbody><tr>
<td width="10">
</td>
<td width="85%">
<font face="Verdana, Arial, Helvetica, sans-serif" size="6"><b>Primitives</b></font>
</td>
<td width="112"><a href="http://spirit.sf.net"><img src="theme/spirit.gif" align="right" border="0" height="48" width="112"></a></td>
</tr>
</tbody></table>
<br>
<table border="0">
<tbody><tr>
<td width="10"></td>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
<td width="30"><a href="organization.html"><img src="theme/l_arr.gif" border="0"></a></td>
<td width="30"><a href="operators.html"><img src="theme/r_arr.gif" border="0"></a></td>
</tr>
</tbody></table>
<p>The framework predefines some parser primitives. These are the most basic building
blocks that the client uses to build more complex parsers. These primitive parsers
are template classes, making them very flexible.</p>
<p>These primitive parsers can be instantiated directly or through a templatized
helper function. Generally, the helper function is far simpler to deal with
as it involves less typing.</p>
<p>We have seen the character literal parser before through the generator function
<tt>ch_p</tt> which is not really a parser but, rather, a parser generator.
Class <tt>chlit&lt;CharT&gt;</tt> is the actual template class behind the character
literal parser. To instantiate a <tt>chlit</tt> object, you must explicitly
provide the character type, <tt>CharT</tt>, as a template parameter which determines
the type of the character. This type typically corresponds to the input type,
usually <tt>char</tt> or <tt>wchar_t</tt>. The following expression creates
a temporary parser object which will recognize the single letter <span class="quotes">'X'</span>.</p>
<pre><code><font color="#000000"><span class="identifier"> </span><span class="identifier">chlit</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;(</span><span class="literal">'X'</span><span class="special">);</span></font></code></pre>
<p>Using <tt>chlit</tt>'s generator function <tt>ch_p</tt> simplifies the usage
of the <tt>chlit&lt;&gt;</tt> class (this is true of most Spirit parser classes
since most have corresponding generator functions). It is convenient to call
the function because the compiler will deduce the template type through argument
deduction for us. The example above could be expressed less verbosely using
the <tt>ch_p </tt>helper function. </p>
<pre><code><font color="#000000"><span class="special"> </span><span class="identifier">ch_p</span><span class="special">(</span><span class="literal">'X'</span><span class="special">) </span><span class="comment">// equivalent to chlit&lt;char&gt;('X') object</span></font></code></pre>
<table align="center" border="0" width="80%">
<tbody><tr>
<td class="note_box"><img src="theme/lens.gif" height="16" width="15"> <b>Parser
generators</b><br>
<br>
Whenever you see an invocation of the parser generator function, it is equivalent
to the parser itself. Therefore, we often call <tt>ch_p</tt> a character
parser, even if, technically speaking, it is a function that generates a
character parser.</td>
</tr>
</tbody></table>
<p>The following grammar snippet shows these forms in action:</p>
<pre><code><span class="comment"> </span><span class="comment">// a rule can "store" a parser object. They're covered<br> </span><span class="comment">// later, but for now just consider a rule as an opaque type<br> </span><span class="identifier">rule</span><span class="special">&lt;&gt; </span><span class="identifier">r1</span><span class="special">, </span><span class="identifier">r2</span><span class="special">, </span><span class="identifier">r3</span><span class="special">;<br><br> </span><span class="identifier">chlit</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt; </span><span class="identifier">x</span><span class="special">(</span><span class="literal">'X'</span><span class="special">); </span><span class="comment">// declare a parser named x<br><br> </span><span class="identifier">r1 </span><span class="special">= </span><span class="identifier">chlit</span><span class="special">&lt;</span><span class="keyword">char</span><span class="special">&gt;(</span><span class="literal">'X'</span><span class="special">); </span><span class="comment">// explicit declaration<br> </span><span class="identifier">r2 </span><span class="special">= </span><span class="identifier">x</span><span class="special">; </span><span class="comment">// using x<br> </span><span class="identifier">r3 </span><span class="special">= </span><span class="identifier">ch_p</span><span class="special">(</span><span class="literal">'X'</span><span class="special">) </span><span class="comment">// using the generator</span></code></pre>
<h2> chlit and ch_p</h2>
<p>Matches a single character literal. <tt>chlit</tt> has a single template type
parameter which defaults to <tt>char</tt> (i.e. <tt>chlit&lt;&gt;</tt> is equivalent
to <tt>chlit&lt;char&gt;</tt>). This type parameter is the character type that
<tt>chlit</tt> will recognize when parsing. The function generator version deduces
the template type parameters from the actual function arguments. The <tt>chlit</tt>
class constructor accepts a single parameter: the character it will match the
input against. Examples:</p>
<pre><code><span class="comment"> </span><span class="identifier">r1 </span><span class="special">= </span><span class="identifier">chlit</span><span class="special">&lt;&gt;(</span><span class="literal">'X'</span><span class="special">);<br> </span><span class="identifier">r2 </span><span class="special">= </span><span class="identifier">chlit</span><span class="special">&lt;</span><span class="keyword">wchar_t</span><span class="special">&gt;(</span><span class="identifier">L</span><span class="literal">'X'</span><span class="special">);<br> </span><span class="identifier">r3 </span><span class="special">= </span><span class="identifier">ch_p</span><span class="special">(</span><span class="literal">'X'</span><span class="special">);</span></code></pre>
<p>Going back to our original example:</p>
<pre><code><span class="special"> </span><span class="identifier">group </span><span class="special">= </span><span class="literal">'(' </span><span class="special">&gt;&gt; </span><span class="identifier">expr </span><span class="special">&gt;&gt; </span><span class="literal">')'</span><span class="special">;<br> </span><span class="identifier">expr1 </span><span class="special">= </span><span class="identifier">integer </span><span class="special">| </span><span class="identifier">group</span><span class="special">;<br> </span><span class="identifier">expr2 </span><span class="special">= </span><span class="identifier">expr1 </span><span class="special">&gt;&gt; </span><span class="special">*((</span><span class="literal">'*' </span><span class="special">&gt;&gt; </span><span class="identifier">expr1</span><span class="special">) </span><span class="special">| </span><span class="special">(</span><span class="literal">'/' </span><span class="special">&gt;&gt; </span><span class="identifier">expr1</span><span class="special">));<br> </span><span class="identifier">expr </span><span class="special">= </span><span class="identifier">expr2 </span><span class="special">&gt;&gt; </span><span class="special">*((</span><span class="literal">'+' </span><span class="special">&gt;&gt; </span><span class="identifier">expr2</span><span class="special">) </span><span class="special">| </span><span class="special">(</span><span class="literal">'-' </span><span class="special">&gt;&gt; </span><span class="identifier">expr2</span><span class="special">));</span></code></pre>
<p></p>
<p>the character literals <tt class="quotes">'('</tt>, <tt class="quotes">')'</tt>,
<tt class="quotes">'+'</tt>, <tt class="quotes">'-'</tt>, <tt class="quotes">'*'</tt>
and <tt class="quotes">'/'</tt> in the grammar declaration are <tt>chlit</tt>
objects that are implicitly created behind the scenes.</p>
<table align="center" border="0" width="80%">
<tbody><tr>
<td class="note_box"><img src="theme/lens.gif" height="16" width="15"> <b>char
operands</b> <br>
<br>
The reason this works is from two special templatized overloads of <tt>operator<span class="operators">&gt;&gt;</span></tt>
that takes a (<tt>char</tt>, <tt> ParserT</tt>), or (<tt>ParserT</tt>, <tt>char</tt>).
These functions convert the character into a <tt>chlit</tt> object.</td>
</tr>
</tbody></table>
<p> One may prefer to declare these explicitly as:</p>
<pre><code><span class="special"> </span><span class="identifier">chlit</span><span class="special">&lt;&gt; </span><span class="identifier">plus</span><span class="special">(</span><span class="literal">'+'</span><span class="special">);<br> </span><span class="identifier">chlit</span><span class="special">&lt;&gt; </span><span class="identifier">minus</span><span class="special">(</span><span class="literal">'-'</span><span class="special">);<br> </span><span class="identifier">chlit</span><span class="special">&lt;&gt; </span><span class="identifier">times</span><span class="special">(</span><span class="literal">'*'</span><span class="special">);<br> </span><span class="identifier">chlit</span><span class="special">&lt;&gt; </span><span class="identifier">divide</span><span class="special">(</span><span class="literal">'/'</span><span class="special">);<br> </span><span class="identifier">chlit</span><span class="special">&lt;&gt; </span><span class="identifier">oppar</span><span class="special">(</span><span class="literal">'('</span><span class="special">);<br> </span><span class="identifier">chlit</span><span class="special">&lt;&gt; </span><span class="identifier">clpar</span><span class="special">(</span><span class="literal">')'</span><span class="special">);</span></code></pre>
<h2>range and range_p</h2>
<p>A <tt>range</tt> of characters is created from a low/high character pair. Such
a parser matches a single character that is in the <tt>range</tt>, including
both endpoints. Like <tt>chlit</tt>, <tt>range</tt> has a single template type
parameter which defaults to <tt>char</tt>. The <tt>range</tt> class constructor
accepts two parameters: the character range (<i>from</i> and <i>to</i>, inclusive)
it will match the input against. The function generator version is <tt>range_p</tt>.
Examples:</p>
<pre><code><span class="special"> </span><span class="identifier">range</span><span class="special">&lt;&gt;(</span><span class="literal">'A'</span><span class="special">,</span><span class="literal">'Z'</span><span class="special">) </span><span class="comment">// matches 'A'..'Z'<br> </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">) </span><span class="comment">// matches 'a'..'z'</span></code></pre>
<p>Note, the first character must be "before" the second, according
to the underlying character encoding characters. The range, like chlit is a
single character parser.</p>
<table align="center" border="0" width="80%">
<tbody><tr>
<td class="note_box"><img src="theme/alert.gif" height="16" width="16"><b>
Character mapping</b><br>
<br>
Character mapping to is inherently platform dependent. It is not guaranteed
in the standard for example that 'A' &lt; 'Z', however, in many occasions,
we are well aware of the character set we are using such as ASCII, ISO-8859-1
or Unicode. Take care though when porting to another platform.</td>
</tr>
</tbody></table>
<h2> strlit and str_p</h2>
<p>This parser matches a string literal. <tt>strlit</tt> has a single template
type parameter: an iterator type. Internally, <tt>strlit</tt> holds a begin/end
iterator pair pointing to a string or a container of characters. The <tt>strlit</tt>
attempts to match the current input stream with this string. The template type
parameter defaults to <tt>char const<span class="operators">*</span></tt>. <tt>strlit</tt>
has two constructors. The first accepts a null-terminated character pointer.
This constructor may be used to build <tt>strlits</tt> from quoted string literals.
The second constructor takes in a first/last iterator pair. The function generator
version is <tt>str_p</tt>. Examples:</p>
<pre><code><span class="comment"> </span><span class="identifier">strlit</span><span class="special">&lt;&gt;(</span><span class="string">"Hello World"</span><span class="special">)<br> </span><span class="identifier">str_p</span><span class="special">(</span><span class="string">"Hello World"</span><span class="special">)<br><br> </span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string </span><span class="identifier">msg</span><span class="special">(</span><span class="string">"Hello World"</span><span class="special">);<br> </span><span class="identifier">strlit</span><span class="special">&lt;</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">::</span><span class="identifier">const_iterator</span><span class="special">&gt;(</span><span class="identifier">msg</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(), </span><span class="identifier">msg</span><span class="special">.</span><span class="identifier">end</span><span class="special">());</span></code></pre>
<table align="center" border="0" width="80%">
<tbody><tr>
<td class="note_box"><img src="theme/note.gif" height="16" width="16"> <b>Character
and phrase level parsing</b><br>
<br>
Typical parsers regard the processing of characters (symbols that form words
or lexemes) and phrases (words that form sentences) as separate domains.
Entities such as reserved words, operators, literal strings, numerical constants,
etc., which constitute the terminals of a grammar are usually extracted
first in a separate lexical analysis stage.<br>
<br>
At this point, as evident in the examples we have so far, it is important
to note that, contrary to standard practice, the Spirit framework handles
parsing tasks at both the character level as well as the phrase level. One
may consider that a lexical analyzer is seamlessly integrated in the Spirit
framework.<br>
<br>
Although the Spirit parser library does not need a separate lexical analyzer,
there is no reason why we cannot have one. One can always have as many parser
layers as needed. In theory, one may create a preprocessor, a lexical analyzer
and a parser proper, all using the same framework.</td>
</tr>
</tbody></table>
<h2>chseq and chseq_p</h2>
<p>Matches a character sequence. <tt>chseq</tt> has the same template type parameters
and constructor parameters as strlit. The function generator version is <tt>chseq_p</tt>.
Examples:</p>
<pre><code><span class="special"> </span><span class="identifier">chseq</span><span class="special">&lt;&gt;(</span><span class="string">"ABCDEFG"</span><span class="special">)<br> </span><span class="identifier">chseq_p</span><span class="special">(</span><span class="string">"ABCDEFG"</span><span class="special">)</span></code></pre>
<p><tt>strlit</tt> is an implicit lexeme. That is, it works solely on the character
level. <tt>chseq</tt>, <tt>strlit</tt>'s twin, on the other hand, can work on
both the character and phrase levels. What this simply means is that it can
ignore white spaces in between the string characters. For example:</p>
<pre><code><span class="special"> </span><span class="identifier">chseq</span><span class="special">&lt;&gt;(</span><span class="string">"ABCDEFG"</span><span class="special">)</span></code></pre>
<p>can parse:</p>
<pre><span class="special"> </span><span class="identifier">ABCDEFG<br> </span><span class="identifier">A </span><span class="identifier">B </span><span class="identifier">C </span><span class="identifier">D </span><span class="identifier">E </span><span class="identifier">F </span><span class="identifier">G<br> </span><span class="identifier">AB </span><span class="identifier">CD </span><span class="identifier">EFG</span></pre>
<h2>More character parsers</h2>
<p>The framework also predefines the full repertoire of single character parsers:</p>
<table align="center" border="0" width="90%">
<tbody><tr>
<td class="table_title" colspan="2">Single character parsers</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>anychar_p</b></td>
<td class="table_cells" width="70%">Matches any single character (including
the null terminator: '\0')</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>alnum_p</b></td>
<td class="table_cells" width="70%">Matches alpha-numeric characters</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>alpha_p</b></td>
<td class="table_cells" width="70%">Matches alphabetic characters</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>blank_p</b></td>
<td class="table_cells" width="70%">Matches spaces or tabs</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>cntrl_p</b></td>
<td class="table_cells" width="70%">Matches control characters</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>digit_p</b></td>
<td class="table_cells" width="70%">Matches numeric digits</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>graph_p</b></td>
<td class="table_cells" width="70%">Matches non-space printing characters</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>lower_p</b></td>
<td class="table_cells" width="70%">Matches lower case letters</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>print_p</b></td>
<td class="table_cells" width="70%">Matches printable characters</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>punct_p</b></td>
<td class="table_cells" width="70%">Matches punctuation symbols</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>space_p</b></td>
<td class="table_cells" width="70%">Matches spaces, tabs, returns, and newlines</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>upper_p</b></td>
<td class="table_cells" width="70%">Matches upper case letters</td>
</tr>
<tr>
<td class="table_cells" width="30%"><b>xdigit_p</b></td>
<td class="table_cells" width="70%">Matches hexadecimal digits</td>
</tr>
</tbody></table>
<h2><a name="negation"></a>negation ~</h2>
<p>Single character parsers such as the <tt>chlit</tt>, <tt>range</tt>, <tt>anychar_p</tt>,
<tt>alnum_p</tt> etc. can be negated. For example:</p>
<pre><code><span class="special"> ~</span><span class="identifier">ch_p</span><span class="special">(</span><span class="literal">'x'</span><span class="special">)</span></code></pre>
<p>matches any character except <tt>'x'</tt>. Double negation of a character parser
cancels out the negation. <tt>~~alpha_p</tt> is equivalent to <tt>alpha_p</tt>.</p>
<h2>eol_p</h2>
<p>Matches the end of line (CR/LF and combinations thereof).</p>
<h2><b>nothing_p</b></h2>
<p>Never matches anything and always fails.</p>
<h2>end_p</h2>
<p>Matches the end of input (returns a sucessful match with 0 length when the
input is exhausted)</p><h2>eps_p</h2>
<p>The <strong>Epsilon</strong> (<tt>epsilon_p</tt> and <tt>eps_p</tt>) is a multi-purpose
parser that returns a zero length match. See <a href="epsilon.html">Epsilon</a> for details.</p><p></p>
<table border="0">
<tbody><tr>
<td width="10"></td>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
<td width="30"><a href="organization.html"><img src="theme/l_arr.gif" border="0"></a></td>
<td width="30"><a href="operators.html"><img src="theme/r_arr.gif" border="0"></a></td>
</tr>
</tbody></table>
<br>
<hr size="1">
<p class="copyright">Copyright <20> 1998-2003 Joel de Guzman<br>
Copyright <20> 2003 Martin Wille<br>
<br>
<font size="2">Use, modification and distribution is subject to the Boost Software
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
http://www.boost.org/LICENSE_1_0.txt) </font> </p>
<p>&nbsp;</p>
</body></html>
Reference in New Issue View Git Blame Copy Permalink