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<?xml version="1.0" encoding="utf-8"?>
<chapter xml:id="parle.pattern.matching" xmlns="http://docbook.org/ns/docbook">
<title>Parle pattern matching</title>
<titleabbrev>Pattern matching</titleabbrev>
<para>
Parle supports regex matching similar to flex.
Also supported are the following POSIX character sets:
<simplelist type="inline">
<member><literal>[:alnum:]</literal></member>
<member><literal>[:alpha:]</literal></member>
<member><literal>[:blank:]</literal></member>
<member><literal>[:cntrl:]</literal></member>
<member><literal>[:digit:]</literal></member>
<member><literal>[:graph:]</literal></member>
<member><literal>[:lower:]</literal></member>
<member><literal>[:print:]</literal></member>
<member><literal>[:punct:]</literal></member>
<member><literal>[:space:]</literal></member>
<member><literal>[:upper:]</literal></member>
<member><literal>[:xdigit:]</literal></member>
</simplelist>
.
</para>
<para>
The Unicode character classes are currently not enabled by default, pass --enable-parle-utf32 to make them available.
A particular encoding can be mapped with a correctly constructed regex.
For example, to match the EURO symbol encoded in UTF-8, the regular expression <literal>[\xe2][\x82][\xac]</literal> can be used.
The pattern for an UTF-8 encoded string could be <literal>[ -\x7f]{+}[\x80-\xbf]{+}[\xc2-\xdf]{+}[\xe0-\xef]{+}[\xf0-\xff]+</literal>.
</para>
<section xml:id="parle.regex.chars" annotations="chunk:false">
<title>Character representations</title>
<para>
<table>
<title>Character representations</title>
<tgroup cols="2">
<thead>
<row>
<entry>Sequence</entry><entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>\a</entry><entry>Alert (bell).</entry>
</row>
<row>
<entry>\b</entry><entry>Backspace.</entry>
</row>
<row>
<entry>\e</entry><entry>ESC character, \x1b.</entry>
</row>
<row>
<entry>\n</entry><entry>Newline.</entry>
</row>
<row>
<entry>\r</entry><entry>Carriage return.</entry>
</row>
<row>
<entry>\f</entry><entry>Form feed, \x0c.</entry>
</row>
<row>
<entry>\t</entry><entry>Horizontal tab, \x09.</entry>
</row>
<row>
<entry>\v</entry><entry>Vertical tab, \x0b.</entry>
</row>
<row>
<entry>\oct</entry><entry>Character specified by a three-digit octal code.</entry>
</row>
<row>
<entry>\xhex</entry><entry>Character specified by a hex code.</entry>
</row>
<row>
<entry>\cchar</entry><entry>Named control character.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</section>
<section xml:id="parle.regex.charclass" annotations="chunk:false">
<title>Character classes</title>
<para>
<table>
<title>Character classes</title>
<tgroup cols="2">
<thead>
<row>
<entry>Sequence</entry><entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>[...]</entry><entry>A single character listed or contained within a listed range. Ranges can be combined with the <literal>{+}</literal> and <literal>{-}</literal> operators. For example <literal>[a-z]{+}[0-9]</literal> is the same as <literal>[0-9a-z]</literal> and <literal>[a-z]{-}[aeiou]</literal> is the same as <literal>[b-df-hj-np-tv-z]</literal>.</entry>
</row>
<row>
<entry>[^...]</entry><entry>A single character not listed and not contained within a listed range.</entry>
</row>
<row>
<entry>.</entry><entry>Any character, default <literal>[^\n].</literal></entry>
</row>
<row>
<entry>\d</entry><entry>Digit character, <literal>[0-9]</literal>.</entry>
</row>
<row>
<entry>\D</entry><entry>Non-digit character, <literal>[^0-9]</literal>.</entry>
</row>
<row>
<entry>\s</entry><entry>White space character, <literal>[ \t\n\r\f\v]</literal>.</entry>
</row>
<row>
<entry>\S</entry><entry>Non-white space character, <literal>[^ \t\n\r\f\v]</literal>.</entry>
</row>
<row>
<entry>\w</entry><entry>Word character, <literal>[a-zA-Z0-9_]</literal>.</entry>
</row>
<row>
<entry>\W</entry><entry>Non-word character, <literal>[^a-zA-Z0-9_]</literal>.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</section>
<section xml:id="parle.regex.unicodecharclass" annotations="chunk:false">
<title>Unicode character classes</title>
<para>
<table>
<title>Unicode character classes</title>
<tgroup cols="2">
<thead>
<row>
<entry>Sequence</entry><entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>\p{C}</entry><entry>Other.</entry>
</row>
<row>
<entry>\p{Cc}</entry><entry>Other, control.</entry>
</row>
<row>
<entry>\p{Cf}</entry><entry>Other, format.</entry>
</row>
<row>
<entry>\p{Co}</entry><entry>Other, private use.</entry>
</row>
<row>
<entry>\p{Cs}</entry><entry>Other, surrogate.</entry>
</row>
<row>
<entry>\p{L}</entry><entry>Letter.</entry>
</row>
<row>
<entry>\p{LC}</entry><entry>Letter, cased.</entry>
</row>
<row>
<entry>\p{Ll}</entry><entry>Letter, lowercase.</entry>
</row>
<row>
<entry>\p{Lm}</entry><entry>Letter, modifier.</entry>
</row>
<row>
<entry>\p{Lo}</entry><entry>Letter, other.</entry>
</row>
<row>
<entry>\p{Lt}</entry><entry>Letter, titlecase.</entry>
</row>
<row>
<entry>\p{Lu}</entry><entry>Letter, uppercase.</entry>
</row>
<row>
<entry>\p{M}</entry><entry>Mark.</entry>
</row>
<row>
<entry>\p{Mc}</entry><entry>Mark, space combining.</entry>
</row>
<row>
<entry>\p{Me}</entry><entry>Mark, enclosing.</entry>
</row>
<row>
<entry>\p{Mn}</entry><entry>Mark, nonspacing.</entry>
</row>
<row>
<entry>\p{N}</entry><entry>Number.</entry>
</row>
<row>
<entry>\p{Nd}</entry><entry>Number, decimal digit.</entry>
</row>
<row>
<entry>\p{Nl}</entry><entry>Number, letter.</entry>
</row>
<row>
<entry>\p{No}</entry><entry>Number, other.</entry>
</row>
<row>
<entry>\p{P}</entry><entry>Punctuation.</entry>
</row>
<row>
<entry>\p{Pc}</entry><entry>Punctiation, connector.</entry>
</row>
<row>
<entry>\p{Pd}</entry><entry>Punctuation, dash.</entry>
</row>
<row>
<entry>\p{Pe}</entry><entry>Punctuation, close.</entry>
</row>
<row>
<entry>\p{Pf}</entry><entry>Punctuation, final quote.</entry>
</row>
<row>
<entry>\p{Pi}</entry><entry>Punctuation, initial quote.</entry>
</row>
<row>
<entry>\p{Po}</entry><entry>Punctuation, other.</entry>
</row>
<row>
<entry>\p{Ps}</entry><entry>Punctuation, open.</entry>
</row>
<row>
<entry>\p{S}</entry><entry>Symbol.</entry>
</row>
<row>
<entry>\p{Sc}</entry><entry>Symbol, currency.</entry>
</row>
<row>
<entry>\p{Sk}</entry><entry>Symbol, modifier.</entry>
</row>
<row>
<entry>\p{Sm}</entry><entry>Symbol, math.</entry>
</row>
<row>
<entry>\p{So}</entry><entry>Symbol, other.</entry>
</row>
<row>
<entry>\p{Z}</entry><entry>Separator.</entry>
</row>
<row>
<entry>\p{Zl}</entry><entry>Separator, line.</entry>
</row>
<row>
<entry>\p{Zp}</entry><entry>Separator, paragraph.</entry>
</row>
<row>
<entry>\p{Zs}</entry><entry>Separator, space.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
These character classes are only available, if the option --enable-parle-utf32 was passed at the compilation time.
</para>
</section>
<section xml:id="parle.regex.alternation" annotations="chunk:false">
<title>Alternation and repetition</title>
<para>
<table>
<title>Alternation and repetition</title>
<tgroup cols="3">
<thead>
<row>
<entry>Sequence</entry><entry>Greedy</entry><entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>...|...</entry><entry>-</entry><entry>Try sub-patterns in alternation.</entry>
</row>
<row>
<entry>*</entry><entry>yes</entry><entry>Match 0 or more times.</entry>
</row>
<row>
<entry>+</entry><entry>yes</entry><entry>Match 1 or more times.</entry>
</row>
<row>
<entry>?</entry><entry>yes</entry><entry>Match 0 or 1 times.</entry>
</row>
<row>
<entry>{n}</entry><entry>no</entry><entry>Match exactly n times.</entry>
</row>
<row>
<entry>{n,}</entry><entry>yes</entry><entry>Match at least n times.</entry>
</row>
<row>
<entry>{n,m}</entry><entry>yes</entry><entry>Match at least n times but no more than m times.</entry>
</row>
<row>
<entry>*?</entry><entry>no</entry><entry>Match 0 or more times.</entry>
</row>
<row>
<entry>+?</entry><entry>no</entry><entry>Match 1 or more times.</entry>
</row>
<row>
<entry>??</entry><entry>no</entry><entry>Match 0 or 1 times.</entry>
</row>
<row>
<entry>{n,}?</entry><entry>no</entry><entry>Match at least n times.</entry>
</row>
<row>
<entry>{n,m}?</entry><entry>no</entry><entry>Match at least n times but no more than m times.</entry>
</row>
<row>
<entry>{MACRO}</entry><entry>-</entry><entry>Include the regex MACRO in the current regex.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</section>
<section xml:id="parle.regex.anchors" annotations="chunk:false">
<title>Anchors</title>
<para>
<table>
<title>Anchors</title>
<tgroup cols="2">
<thead>
<row>
<entry>Sequence</entry><entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>^</entry><entry>Start of string or after a newline.</entry>
</row>
<row>
<entry>$</entry><entry>End of string or before a newline.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</section>
<section xml:id="parle.regex.grouping" annotations="chunk:false">
<title>Grouping</title>
<para>
<table>
<title>Grouping</title>
<tgroup cols="2">
<thead>
<row>
<entry>Sequence</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry>(...)</entry>
<entry>Group a regular expression to override default operator precedence.</entry>
</row>
<row>
<entry valign="top">(?r-s:pattern)</entry>
<entry>
<simpara>
Apply option r and omit option s while interpreting pattern.
Options may be zero or more of the characters i, s, or x.
</simpara>
<simpara>
<literal>i</literal> means case-insensitive.
</simpara>
<simpara>
<literal>-i</literal> means case-sensitive.
</simpara>
<simpara>
<literal>s</literal> alters the meaning of <literal>.</literal> to match any character whatsoever.
</simpara>
<simpara>
<literal>-s</literal> alters the meaning of <literal>.</literal> to match any character except <literal>\n</literal>.
</simpara>
<simpara>
<literal>x</literal> ignores comments and whitespace in patterns.
Whitespace is ignored unless it is backslash-escaped, contained within <literal>""s</literal>,
or appears inside a character range.
</simpara>
<simpara>
These options can be applied globally at the rules level by passing a combination of the bit flags to the lexer.
</simpara>
</entry>
</row>
<row>
<entry>(?# comment )</entry>
<entry>Omit everything within (). The first ) character encountered ends the pattern. It is not possible for the comment to contain a ) character. The comment may span lines.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</section>
</chapter>
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