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      Regex syntax for LPEG
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 <h1>re</h1>

 <ul>
   <li><a href="#basic">Basic Constructions</a></li>
   <li><a href="#func">Functions</a></li>
   <li><a href="#ex">Some Examples</a></li>
   <li><a href="#license">License</a></li>
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 <h2><a name="basic"></a>The <code>re</code> Module</h2>

 <p>
 The <code>re</code> module
 (provided by file <code>re.lua</code> in the distribution)
 supports a somewhat conventional regex syntax
 for pattern usage within <a href="lpeg.html">LPeg</a>.
 </p>

 <p>
 The next table summarizes <code>re</code>'s syntax.
 A <code>p</code> represents an arbitrary pattern;
 <code>num</code> represents a number (<code>[0-9]+</code>);
 <code>name</code> represents an identifier
 (<code>[a-zA-Z][a-zA-Z0-9_]*</code>).
 Constructions are listed in order of decreasing precedence.
 <table border="1">
 <tbody><tr><td><b>Syntax</b></td><td><b>Description</b></td></tr>
 <tr><td><code>( p )</code></td> <td>grouping</td></tr>
 <tr><td><code>'string'</code></td> <td>literal string</td></tr>
 <tr><td><code>"string"</code></td> <td>literal string</td></tr>
 <tr><td><code>[class]</code></td> <td>character class</td></tr>
 <tr><td><code>.</code></td> <td>any character</td></tr>
 <tr><td><code>%name</code></td>
   <td>pattern <code>defs[name]</code> or a pre-defined pattern</td></tr>
 <tr><td><code>name</code></td><td>non terminal</td></tr>
 <tr><td><code>&lt;name&gt;</code></td><td>non terminal</td></tr>
 <tr><td><code>{}</code></td> <td>position capture</td></tr>
 <tr><td><code>{ p }</code></td> <td>simple capture</td></tr>
 <tr><td><code>{: p :}</code></td> <td>anonymous group capture</td></tr>
 <tr><td><code>{:name: p :}</code></td> <td>named group capture</td></tr>
 <tr><td><code>{~ p ~}</code></td> <td>substitution capture</td></tr>
 <tr><td><code>=name</code></td> <td>back reference
 </td></tr>
 <tr><td><code>p ?</code></td> <td>optional match</td></tr>
 <tr><td><code>p *</code></td> <td>zero or more repetitions</td></tr>
 <tr><td><code>p +</code></td> <td>one or more repetitions</td></tr>
 <tr><td><code>p^num</code></td> <td>exactly <code>n</code> repetitions</td></tr>
 <tr><td><code>p^+num</code></td>
       <td>at least <code>n</code> repetitions</td></tr>
 <tr><td><code>p^-num</code></td>
       <td>at most <code>n</code> repetitions</td></tr>
 <tr><td><code>p -&gt; 'string'</code></td> <td>string capture</td></tr>
 <tr><td><code>p -&gt; "string"</code></td> <td>string capture</td></tr>
 <tr><td><code>p -&gt; {}</code></td> <td>table capture</td></tr>
 <tr><td><code>p -&gt; name</code></td> <td>function/query/string capture
 equivalent to <code>p / defs[name]</code></td></tr>
 <tr><td><code>p =&gt; name</code></td> <td>match-time capture
 equivalent to <code>lpeg.Cmt(p, defs[name])</code></td></tr>
 <tr><td><code>& p</code></td> <td>and predicate</td></tr>
 <tr><td><code>! p</code></td> <td>not predicate</td></tr>
 <tr><td><code>p1 p2</code></td> <td>concatenation</td></tr>
 <tr><td><code>p1 / p2</code></td> <td>ordered choice</td></tr>
 <tr><td>(<code>name &lt;- p</code>)<sup>+</sup></td> <td>grammar</td></tr>
 </tbody></table>
 <p>
 Any space appearing in a syntax description can be
 replaced by zero or more space characters and Lua-style comments
 (<code>--</code> until end of line).
 </p>

 <p>
 Character classes define sets of characters.
 An initial <code>^</code> complements the resulting set.
 A range <em>x</em><code>-</code><em>y</em> includes in the set
 all characters with codes between the codes of <em>x</em> and <em>y</em>.
 A pre-defined class <code>%</code><em>name</em> includes all
 characters of that class.
 A simple character includes itself in the set.
 The only special characters inside a class are <code>^</code>
 (special only if it is the first character);
 <code>]</code>
 (can be included in the set as the first character,
 after the optional <code>^</code>);
 <code>%</code> (special only if followed by a letter);
 and <code>-</code>
 (can be included in the set as the first or the last character).
 </p>

 <p>
 Currently the pre-defined classes are similar to those from the
 Lua's string library
 (<code>%a</code> for letters,
 <code>%A</code> for non letters, etc.).
 There is also a class <code>%nl</code>
 containing only the newline character,
 which is particularly handy for grammars written inside long strings,
 as long strings do not interpret escape sequences like <code>\n</code>.
 </p>


 <h2><a name="func">Functions</a></h2>

 <h3><code>re.compile (string, [, defs])</code></h3>
 <p>
 Compiles the given string and
 returns an equivalent LPeg pattern.
 The given string may define either an expression or a grammar.
 The optional <code>defs</code> table provides extra Lua values
 to be used by the pattern.
 </p>

 <h3><code>re.find (subject, pattern [, init])</code></h3>
 <p>
 Searches the given pattern in the given subject.
 If it finds a match,
 returns the index where this occurrence starts,
 plus the captures made by the pattern (if any).
 Otherwise, returns nil.
 </p>

 <p>
 An optional numeric argument <code>init</code> makes the search
 starts at that position in the subject string.
 As usual in Lua libraries,
 a negative value counts from the end.
 </p>

 <h3><code>re.match (subject, pattern)</code></h3>
 <p>
 Matches the given pattern against the given subject.
 </p>

 <h3><code>re.updatelocale ()</code></h3>
 <p>
 Updates the pre-defined character classes to the current locale.
 </p>


 <h2><a name="ex">Some Examples</a></h2>

 <h3>A complete simple program</h3>
 <p>
 The next code shows a simple complete Lua program using
 the <code>re</code> module:
 </p>
 <pre class="example">
 local re = require"re"

 -- find the position of the first number in a string
 print(re.find("the number 423 is odd", "[0-9]+"))  --&gt; 12

 -- similar, but also captures (and returns) the number
 print(re.find("the number 423 is odd", "{[0-9]+}"))  --&gt; 12    423

 -- returns all words in a string
 print(re.match("the number 423 is odd", "({%a+} / .)*"))
 --&gt; the    number    is    odd
 </pre>


 <h3>Balanced parentheses</h3>
 <p>
 The following call will produce the same pattern produced by the
 Lua expression in the
 <a href="lpeg.html#balanced">balanced parentheses</a> example:
 </p>
 <pre class="example">
 b = re.compile[[  balanced &lt;- "(" ([^()] / balanced)* ")"  ]]
 </pre>

 <h3>String reversal</h3>
 <p>
 The next example reverses a string:
 </p>
 <pre class="example">
 rev = re.compile[[ R &lt;- (!.) -&gt; '' / ({.} R) -&gt; '%2%1']]
 print(rev:match"0123456789")   --&gt; 9876543210
 </pre>

 <h3>CSV decoder</h3>
 <p>
 The next example replicates the <a href="lpeg.html#CSV">CSV decoder</a>:
 </p>
 <pre class="example">
 record = re.compile[[
   record &lt;- ( field (',' field)* ) -&gt; {} (%nl / !.)
   field &lt;- escaped / nonescaped
   nonescaped &lt;- { [^,"%nl]* }
   escaped &lt;- '"' {~ ([^"] / '""' -&gt; '"')* ~} '"'
 ]]
 </pre>

 <h3>Lua's long strings</h3>
 <p>
 The next example matches Lua long strings:
 </p>
 <pre class="example">
 c = re.compile([[
   longstring &lt;- ('[' {:eq: '='* :} '[' close) -&gt; void
   close &lt;- ']' =eq ']' / . close
 ]], {void = function () end})

 print(c:match'[==[]]===]]]]==]===[]')   --&gt; 17
 </pre>

 <h3>Abstract Syntax Trees</h3>
 <p>
 This example shows a simple way to build an
 abstract syntax tree (AST) for a given grammar.
 To keep our example simple,
 let us consider the following grammar
 for lists of names:
 </p>
 <pre class="example">
 p = re.compile[[
       listname &lt;- (name s)*
       name &lt;- [a-z][a-z]*
       s &lt;- %s*
 ]]
 </pre>
 <p>
 Now, we will add captures to build a corresponding AST.
 As a first step, the pattern will build a table to
 represent each non terminal;
 terminals will be represented by their corresponding strings:
 </p>
 <pre class="example">
 c = re.compile[[
       listname &lt;- (name s)* -&gt; {}
       name &lt;- {[a-z][a-z]*} -&gt; {}
       s &lt;- %s*
 ]]
 </pre>
 <p>
 Now, a match against <code>"hi hello bye"</code>
 results in the table
 <code>{{"hi"}, {"hello"}, {"bye"}}</code>.
 </p>
 <p>
 For such a simple grammar,
 this AST is more than enough;
 actually, the tables around each single name
 are already overkilling.
 More complex grammars,
 however, may need some more structure.
 Specifically,
 it would be useful if each table had
 a <code>tag</code> field telling what non terminal
 that table represents.
 We can add such a tag using
 <a href="lpeg.html/#cap-g">named group captures</a>:
 </p>
 <pre class="example">
 x = re.compile[[
       listname <- ({:tag: '' -> 'list':} (name s)*) -> {}
       name <- ({:tag: '' -> 'id':} {[a-z][a-z]*}) -> {}
       s <- ' '*
 ]]
 </pre>
 <p>
 With these group captures,
 a match against <code>"hi hello bye"</code>
 results in the following table:
 </p>
 <pre class="example">
 {tag="list",
   {tag="id", "hi"},
   {tag="id", "hello"},
   {tag="id", "bye"}
 }
 </pre>


 <h3>Indented blocks</h3>
 <p>
 This example breaks indented blocks into tables,
 respecting the indentation:
 </p>
 <pre class="example">
 p = re.compile[[
   block &lt;- ({:ident:' '*:} line
            ((=ident !' ' line) / &(=ident ' ') block)*) -&gt; {}
   line &lt;- {[^%nl]*} %nl
 ]]
 </pre>
 <p>
 As an example,
 consider the following text:
 </p>
 <pre class="example">
 t = p:match[[
 first line
   subline 1
   subline 2
 second line
 third line
   subline 3.1
     subline 3.1.1
   subline 3.2
 ]]
 </pre>
 <p>
 The resulting table <code>t</code> will be like this:
 </p>
 <pre class="example">
    {'first line'; {'subline 1'; 'subline 2'; ident = '  '};
     'second line';
     'third line'; { 'subline 3.1'; {'subline 3.1.1'; ident = '    '};
                     'subline 3.2'; ident = '  '};
     ident = ''}
 </pre>

 <h3>Macro expander</h3>
 <p>
 This example implements a simple macro expander.
 Macros must be defined as part of the pattern,
 following some simple rules:
 </p>
 <pre class="example">
 p = re.compile[[
       text &lt;- {~ item* ~}
       item &lt;- macro / [^()] / '(' item* ')'
       arg &lt;- ' '* {~ (!',' item)* ~}
       args &lt;- '(' arg (',' arg)* ')'
       -- now we define some macros
       macro &lt;- ('apply' args) -&gt; '%1(%2)'
              / ('add' args) -&gt; '%1 + %2'
              / ('mul' args) -&gt; '%1 * %2'
 ]]

 print(p:match"add(mul(a,b), apply(f,x))")   --&gt; a * b + f(x)
 </pre>
 <p>
 A <code>text</code> is a sequence of items,
 wherein we apply a substitution capture to expand any macros.
 An <code>item</code> is either a macro,
 any character different from parentheses,
 or a parenthesized expression.
 A macro argument (<code>arg</code>) is a sequence
 of items different from a comma.
 (Note that a comma may appear inside an item,
 e.g., inside a parenthesized expression.)
 Again we do a substitution capture to expand any macro
 in the argument before expanding the outer macro.
 <code>args</code> is a list of arguments separated by commas.
 Finally we define the macros.
 Each macro is a string substitution;
 it replaces the macro name and its arguments by its corresponding string,
 with each <code>%</code><em>n</em> replaced by the <em>n</em>-th argument.
 </p>

 <h3>Patterns</h3>
 <p>
 This example shows the complete syntax
 of patterns accepted by <code>re</code>.
 </p>
 <pre class="example">
 p = [=[

 pattern         &lt;- exp !.
 exp             &lt;- S (alternative / grammar)

 alternative     &lt;- seq ('/' S seq)*
 seq             &lt;- prefix*
 prefix          &lt;- '&amp;' S prefix / '!' S prefix / suffix
 suffix          &lt;- primary S (([+*?]
                             / '^' [+-]? num
                             / '-&gt;' S (string / '{}' / name)
                             / '=&gt;' S name) S)*

 primary         &lt;- '(' exp ')' / string / class / defined
                  / '{:' (name ':')? exp ':}'
                  / '=' name
                  / '{}'
                  / '{~' exp '~}'
                  / '{' exp '}'
                  / '.'
                  / name S !arrow
                  / '&lt;' name '&gt;'          -- old-style non terminals

 grammar         &lt;- definition+
 definition      &lt;- name S arrow exp

 class           &lt;- '[' '^'? item (!']' item)* ']'
 item            &lt;- defined / range / .
 range           &lt;- . '-' [^]]

 S               &lt;- (%s / '--' [^%nl]*)*   -- spaces and comments
 name            &lt;- [A-Za-z][A-Za-z0-9_]*
 arrow           &lt;- '&lt;-'
 num             &lt;- [0-9]+
 string          &lt;- '"' [^"]* '"' / "'" [^']* "'"
 defined         &lt;- '%' name

 ]=]

 print(re.match(p, p))   -- a self description must match itself
 </pre>


 <h2><a name="license">License</a></h2>

 <p>
 Copyright &copy; 2008-2010 Lua.org, PUC-Rio.
 </p>
 <p>
 Permission is hereby granted, free of charge,
 to any person obtaining a copy of this software and
 associated documentation files (the "Software"),
 to deal in the Software without restriction,
 including without limitation the rights to use,
 copy, modify, merge, publish, distribute, sublicense,
 and/or sell copies of the Software,
 and to permit persons to whom the Software is
 furnished to do so,
 subject to the following conditions:
 </p>

 <p>
 The above copyright notice and this permission notice
 shall be included in all copies or substantial portions of the Software.
 </p>

 <p>
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 </p>

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	<head>
	<title>LPeg.re - Regex syntax for LPEG</title>
	<link rel="stylesheet"
	href="http://www.inf.puc-rio.br/~roberto/lpeg/doc.css"
	type="text/css"/>
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	<img alt="LPeg logo" src="lpeg-128.gif"/>
	</a>
	</div>
	<div id="product_name"><big><strong>LPeg.re</strong></big></div>
	<div id="product_description">
	Regex syntax for LPEG
	</div>
	</div> <!-- id="product" -->

	<div id="main">

	<div id="navigation">
	<h1>re</h1>

	<ul>
	<li><a href="#basic">Basic Constructions</a></li>
	<li><a href="#func">Functions</a></li>
	<li><a href="#ex">Some Examples</a></li>
	<li><a href="#license">License</a></li>
	</ul>
	</li>
	</ul>
	</div> <!-- id="navigation" -->

	<div id="content">

	<h2><a name="basic"></a>The <code>re</code> Module</h2>

	<p>
	The <code>re</code> module
	(provided by file <code>re.lua</code> in the distribution)
	supports a somewhat conventional regex syntax
	for pattern usage within <a href="lpeg.html">LPeg</a>.
	</p>

	<p>
	The next table summarizes <code>re</code>'s syntax.
	A <code>p</code> represents an arbitrary pattern;
	<code>num</code> represents a number (<code>[0-9]+</code>);
	<code>name</code> represents an identifier
	(<code>[a-zA-Z][a-zA-Z0-9_]*</code>).
	Constructions are listed in order of decreasing precedence.
	<table border="1">
	<tbody><tr><td><b>Syntax</b></td><td><b>Description</b></td></tr>
	<tr><td><code>( p )</code></td> <td>grouping</td></tr>
	<tr><td><code>'string'</code></td> <td>literal string</td></tr>
	<tr><td><code>"string"</code></td> <td>literal string</td></tr>
	<tr><td><code>[class]</code></td> <td>character class</td></tr>
	<tr><td><code>.</code></td> <td>any character</td></tr>
	<tr><td><code>%name</code></td>
	<td>pattern <code>defs[name]</code> or a pre-defined pattern</td></tr>
	<tr><td><code>name</code></td><td>non terminal</td></tr>
	<tr><td><code><name></code></td><td>non terminal</td></tr>
	<tr><td><code>{}</code></td> <td>position capture</td></tr>
	<tr><td><code>{ p }</code></td> <td>simple capture</td></tr>
	<tr><td><code>{: p :}</code></td> <td>anonymous group capture</td></tr>
	<tr><td><code>{:name: p :}</code></td> <td>named group capture</td></tr>
	<tr><td><code>{~ p ~}</code></td> <td>substitution capture</td></tr>
	<tr><td><code>=name</code></td> <td>back reference
	</td></tr>
	<tr><td><code>p ?</code></td> <td>optional match</td></tr>
	<tr><td><code>p *</code></td> <td>zero or more repetitions</td></tr>
	<tr><td><code>p +</code></td> <td>one or more repetitions</td></tr>
	<tr><td><code>p^num</code></td> <td>exactly <code>n</code> repetitions</td></tr>
	<tr><td><code>p^+num</code></td>
	<td>at least <code>n</code> repetitions</td></tr>
	<tr><td><code>p^-num</code></td>
	<td>at most <code>n</code> repetitions</td></tr>
	<tr><td><code>p -> 'string'</code></td> <td>string capture</td></tr>
	<tr><td><code>p -> "string"</code></td> <td>string capture</td></tr>
	<tr><td><code>p -> {}</code></td> <td>table capture</td></tr>
	<tr><td><code>p -> name</code></td> <td>function/query/string capture
	equivalent to <code>p / defs[name]</code></td></tr>
	<tr><td><code>p => name</code></td> <td>match-time capture
	equivalent to <code>lpeg.Cmt(p, defs[name])</code></td></tr>
	<tr><td><code>& p</code></td> <td>and predicate</td></tr>
	<tr><td><code>! p</code></td> <td>not predicate</td></tr>
	<tr><td><code>p1 p2</code></td> <td>concatenation</td></tr>
	<tr><td><code>p1 / p2</code></td> <td>ordered choice</td></tr>
	<tr><td>(<code>name <- p</code>)<sup>+</sup></td> <td>grammar</td></tr>
	</tbody></table>
	<p>
	Any space appearing in a syntax description can be
	replaced by zero or more space characters and Lua-style comments
	(<code>--</code> until end of line).
	</p>

	<p>
	Character classes define sets of characters.
	An initial <code>^</code> complements the resulting set.
	A range <em>x</em><code>-</code><em>y</em> includes in the set
	all characters with codes between the codes of <em>x</em> and <em>y</em>.
	A pre-defined class <code>%</code><em>name</em> includes all
	characters of that class.
	A simple character includes itself in the set.
	The only special characters inside a class are <code>^</code>
	(special only if it is the first character);
	<code>]</code>
	(can be included in the set as the first character,
	after the optional <code>^</code>);
	<code>%</code> (special only if followed by a letter);
	and <code>-</code>
	(can be included in the set as the first or the last character).
	</p>

	<p>
	Currently the pre-defined classes are similar to those from the
	Lua's string library
	(<code>%a</code> for letters,
	<code>%A</code> for non letters, etc.).
	There is also a class <code>%nl</code>
	containing only the newline character,
	which is particularly handy for grammars written inside long strings,
	as long strings do not interpret escape sequences like <code>\n</code>.
	</p>


	<h2><a name="func">Functions</a></h2>

	<h3><code>re.compile (string, [, defs])</code></h3>
	<p>
	Compiles the given string and
	returns an equivalent LPeg pattern.
	The given string may define either an expression or a grammar.
	The optional <code>defs</code> table provides extra Lua values
	to be used by the pattern.
	</p>

	<h3><code>re.find (subject, pattern [, init])</code></h3>
	<p>
	Searches the given pattern in the given subject.
	If it finds a match,
	returns the index where this occurrence starts,
	plus the captures made by the pattern (if any).
	Otherwise, returns nil.
	</p>

	<p>
	An optional numeric argument <code>init</code> makes the search
	starts at that position in the subject string.
	As usual in Lua libraries,
	a negative value counts from the end.
	</p>

	<h3><code>re.match (subject, pattern)</code></h3>
	<p>
	Matches the given pattern against the given subject.
	</p>

	<h3><code>re.updatelocale ()</code></h3>
	<p>
	Updates the pre-defined character classes to the current locale.
	</p>


	<h2><a name="ex">Some Examples</a></h2>

	<h3>A complete simple program</h3>
	<p>
	The next code shows a simple complete Lua program using
	the <code>re</code> module:
	</p>
	<pre class="example">
	local re = require"re"

	-- find the position of the first number in a string
	print(re.find("the number 423 is odd", "[0-9]+")) --> 12

	-- similar, but also captures (and returns) the number
	print(re.find("the number 423 is odd", "{[0-9]+}")) --> 12 423

	-- returns all words in a string
	print(re.match("the number 423 is odd", "({%a+} / .)*"))
	--> the number is odd
	</pre>


	<h3>Balanced parentheses</h3>
	<p>
	The following call will produce the same pattern produced by the
	Lua expression in the
	<a href="lpeg.html#balanced">balanced parentheses</a> example:
	</p>
	<pre class="example">
	b = re.compile[[ balanced <- "(" ([^()] / balanced)* ")" ]]
	</pre>

	<h3>String reversal</h3>
	<p>
	The next example reverses a string:
	</p>
	<pre class="example">
	rev = re.compile[[ R <- (!.) -> '' / ({.} R) -> '%2%1']]
	print(rev:match"0123456789") --> 9876543210
	</pre>

	<h3>CSV decoder</h3>
	<p>
	The next example replicates the <a href="lpeg.html#CSV">CSV decoder</a>:
	</p>
	<pre class="example">
	record = re.compile[[
	record <- ( field (',' field)* ) -> {} (%nl / !.)
	field <- escaped / nonescaped
	nonescaped <- { [^,"%nl]* }
	escaped <- '"' {~ ([^"] / '""' -> '"')* ~} '"'
	]]
	</pre>

	<h3>Lua's long strings</h3>
	<p>
	The next example matches Lua long strings:
	</p>
	<pre class="example">
	c = re.compile([[
	longstring <- ('[' {:eq: '='* :} '[' close) -> void
	close <- ']' =eq ']' / . close
	]], {void = function () end})

	print(c:match'[==[]]===]]]]==]===[]') --> 17
	</pre>

	<h3>Abstract Syntax Trees</h3>
	<p>
	This example shows a simple way to build an
	abstract syntax tree (AST) for a given grammar.
	To keep our example simple,
	let us consider the following grammar
	for lists of names:
	</p>
	<pre class="example">
	p = re.compile[[
	listname <- (name s)*
	name <- [a-z][a-z]*
	s <- %s*
	]]
	</pre>
	<p>
	Now, we will add captures to build a corresponding AST.
	As a first step, the pattern will build a table to
	represent each non terminal;
	terminals will be represented by their corresponding strings:
	</p>
	<pre class="example">
	c = re.compile[[
	listname <- (name s)* -> {}
	name <- {[a-z][a-z]*} -> {}
	s <- %s*
	]]
	</pre>
	<p>
	Now, a match against <code>"hi hello bye"</code>
	results in the table
	<code>{{"hi"}, {"hello"}, {"bye"}}</code>.
	</p>
	<p>
	For such a simple grammar,
	this AST is more than enough;
	actually, the tables around each single name
	are already overkilling.
	More complex grammars,
	however, may need some more structure.
	Specifically,
	it would be useful if each table had
	a <code>tag</code> field telling what non terminal
	that table represents.
	We can add such a tag using
	<a href="lpeg.html/#cap-g">named group captures</a>:
	</p>
	<pre class="example">
	x = re.compile[[
	listname <- ({:tag: '' -> 'list':} (name s)*) -> {}
	name <- ({:tag: '' -> 'id':} {[a-z][a-z]*}) -> {}
	s <- ' '*
	]]
	</pre>
	<p>
	With these group captures,
	a match against <code>"hi hello bye"</code>
	results in the following table:
	</p>
	<pre class="example">
	{tag="list",
	{tag="id", "hi"},
	{tag="id", "hello"},
	{tag="id", "bye"}
	}
	</pre>


	<h3>Indented blocks</h3>
	<p>
	This example breaks indented blocks into tables,
	respecting the indentation:
	</p>
	<pre class="example">
	p = re.compile[[
	block <- ({:ident:' '*:} line
	((=ident !' ' line) / &(=ident ' ') block)*) -> {}
	line <- {[^%nl]*} %nl
	]]
	</pre>
	<p>
	As an example,
	consider the following text:
	</p>
	<pre class="example">
	t = p:match[[
	first line
	subline 1
	subline 2
	second line
	third line
	subline 3.1
	subline 3.1.1
	subline 3.2
	]]
	</pre>
	<p>
	The resulting table <code>t</code> will be like this:
	</p>
	<pre class="example">
	{'first line'; {'subline 1'; 'subline 2'; ident = ' '};
	'second line';
	'third line'; { 'subline 3.1'; {'subline 3.1.1'; ident = ' '};
	'subline 3.2'; ident = ' '};
	ident = ''}
	</pre>

	<h3>Macro expander</h3>
	<p>
	This example implements a simple macro expander.
	Macros must be defined as part of the pattern,
	following some simple rules:
	</p>
	<pre class="example">
	p = re.compile[[
	text <- {~ item* ~}
	item <- macro / [^()] / '(' item* ')'
	arg <- ' '* {~ (!',' item)* ~}
	args <- '(' arg (',' arg)* ')'
	-- now we define some macros
	macro <- ('apply' args) -> '%1(%2)'
	/ ('add' args) -> '%1 + %2'
	/ ('mul' args) -> '%1 * %2'
	]]

	print(p:match"add(mul(a,b), apply(f,x))") --> a * b + f(x)
	</pre>
	<p>
	A <code>text</code> is a sequence of items,
	wherein we apply a substitution capture to expand any macros.
	An <code>item</code> is either a macro,
	any character different from parentheses,
	or a parenthesized expression.
	A macro argument (<code>arg</code>) is a sequence
	of items different from a comma.
	(Note that a comma may appear inside an item,
	e.g., inside a parenthesized expression.)
	Again we do a substitution capture to expand any macro
	in the argument before expanding the outer macro.
	<code>args</code> is a list of arguments separated by commas.
	Finally we define the macros.
	Each macro is a string substitution;
	it replaces the macro name and its arguments by its corresponding string,
	with each <code>%</code><em>n</em> replaced by the <em>n</em>-th argument.
	</p>

	<h3>Patterns</h3>
	<p>
	This example shows the complete syntax
	of patterns accepted by <code>re</code>.
	</p>
	<pre class="example">
	p = [=[

	pattern <- exp !.
	exp <- S (alternative / grammar)

	alternative <- seq ('/' S seq)*
	seq <- prefix*
	prefix <- '&' S prefix / '!' S prefix / suffix
	suffix <- primary S (([+*?]
	/ '^' [+-]? num
	/ '->' S (string / '{}' / name)
	/ '=>' S name) S)*

	primary <- '(' exp ')' / string / class / defined
	/ '{:' (name ':')? exp ':}'
	/ '=' name
	/ '{}'
	/ '{~' exp '~}'
	/ '{' exp '}'
	/ '.'
	/ name S !arrow
	/ '<' name '>' -- old-style non terminals

	grammar <- definition+
	definition <- name S arrow exp

	class <- '[' '^'? item (!']' item)* ']'
	item <- defined / range / .
	range <- . '-' [^]]

	S <- (%s / '--' [^%nl]) -- spaces and comments
	name <- [A-Za-z][A-Za-z0-9_]*
	arrow <- '<-'
	num <- [0-9]+
	string <- '"' [^"]* '"' / "'" [^']* "'"
	defined <- '%' name

	]=]

	print(re.match(p, p)) -- a self description must match itself
	</pre>



	<h2><a name="license">License</a></h2>

	<p>
	Copyright © 2008-2010 Lua.org, PUC-Rio.
	</p>
	<p>
	Permission is hereby granted, free of charge,
	to any person obtaining a copy of this software and
	associated documentation files (the "Software"),
	to deal in the Software without restriction,
	including without limitation the rights to use,
	copy, modify, merge, publish, distribute, sublicense,
	and/or sell copies of the Software,
	and to permit persons to whom the Software is
	furnished to do so,
	subject to the following conditions:
	</p>

	<p>
	The above copyright notice and this permission notice
	shall be included in all copies or substantial portions of the Software.
	</p>

	<p>
	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	EXPRESS OR IMPLIED,
	INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
	IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
	DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
	TORT OR OTHERWISE, ARISING FROM,
	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	THE SOFTWARE.
	</p>

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