1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"//www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title>LPeg.re - Regex syntax for LPEG</title>
<link rel="stylesheet"
href="//www.inf.puc-rio.br/~roberto/lpeg/doc.css"
type="text/css"/>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
</head>
<body>
<div id="container">
<div id="product">
<div id="product_logo">
<a href="//www.inf.puc-rio.br/~roberto/lpeg/">
<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>& 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>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>num</code> repetitions</td></tr>
<tr><td><code>p^+num</code></td>
<td>at least <code>num</code> repetitions</td></tr>
<tr><td><code>p^-num</code></td>
<td>at most <code>num</code> repetitions</td></tr>
<tr><td>(<code>name <- p</code>)<sup>+</sup></td> <td>grammar</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>{| p |}</code></td> <td>table capture</td></tr>
<tr><td><code>=name</code></td> <td>back reference</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 -> num</code></td> <td>numbered 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 ~> name</code></td> <td>fold capture
(deprecated)</td></tr>
<tr><td><code>p >> name</code></td> <td>accumulator capture
equivalent to <code>(p % defs[name])</code></td></tr>
</tbody></table>
<p>
Any space appearing in a syntax description can be
replaced by zero or more space characters and Lua-style short 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 and
the index where it ends.
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.gsub (subject, pattern, replacement)</code></h3>
<p>
Does a <em>global substitution</em>,
replacing all occurrences of <code>pattern</code>
in the given <code>subject</code> by <code>replacement</code>.
<h3><code>re.match (subject, pattern)</code></h3>
<p>
Matches the given pattern against the given subject,
returning all captures.
</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 numeral in a string
print(re.find("the number 423 is odd", "[0-9]+")) --> 12 14
-- returns all words in a string
print(re.match("the number 423 is odd", "({%a+} / .)*"))
--> the number is odd
-- returns the first numeral in a string
print(re.match("the number 423 is odd", "s <- {%d+} / . s"))
--> 423
-- substitutes a dot for each vowel in a string
print(re.gsub("hello World", "[aeiou]", "."))
--> h.ll. W.rld
</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)
close <- ']' =eq ']' / . close
]])
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 (grammar / alternative)
alternative <- seq ('/' S seq)*
seq <- prefix*
prefix <- '&' S prefix / '!' S prefix / suffix
suffix <- primary S (([+*?]
/ '^' [+-]? num
/ '->' S (string / '{}' / name)
/ '>>' S name
/ '=>' S name) S)*
primary <- '(' exp ')' / string / class / defined
/ '{:' (name ':')? exp ':}'
/ '=' name
/ '{}'
/ '{~' exp '~}'
/ '{|' 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>
This module is part of the <a href="lpeg.html">LPeg</a> package and shares
its <a href="lpeg.html#license">license</a>.
</div> <!-- id="content" -->
</div> <!-- id="main" -->
</div> <!-- id="container" -->
</body>
</html>
|