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Simple Parser Example
=====================
Extend the ``Doctrine\Common\Lexer\AbstractLexer`` class and implement
the ``getCatchablePatterns``, ``getNonCatchablePatterns``, and ``getType``
methods. Here is a very simple example lexer implementation named ``CharacterTypeLexer``.
It tokenizes a string to ``T_UPPER``, ``T_LOWER`` and``T_NUMBER`` tokens:
.. code-block:: php
<?php
use Doctrine\Common\Lexer\AbstractLexer;
/**
* @extends AbstractLexer<CharacterTypeLexer::T_*, string>
*/
class CharacterTypeLexer extends AbstractLexer
{
const T_UPPER = 1;
const T_LOWER = 2;
const T_NUMBER = 3;
protected function getCatchablePatterns(): array
{
return [
'[a-bA-Z0-9]',
];
}
protected function getNonCatchablePatterns(): array
{
return [];
}
protected function getType(&$value): int
{
if (is_numeric($value)) {
return self::T_NUMBER;
}
if (strtoupper($value) === $value) {
return self::T_UPPER;
}
if (strtolower($value) === $value) {
return self::T_LOWER;
}
}
}
Use ``CharacterTypeLexer`` to extract an array of upper case characters:
.. code-block:: php
<?php
class UpperCaseCharacterExtracter
{
public function __construct(private CharacterTypeLexer $lexer)
{
}
/** @return list<string> */
public function getUpperCaseCharacters(string $string): array
{
$this->lexer->setInput($string);
$this->lexer->moveNext();
$upperCaseChars = [];
while (true) {
if (!$this->lexer->lookahead) {
break;
}
$this->lexer->moveNext();
if ($this->lexer->token->isA(CharacterTypeLexer::T_UPPER)) {
$upperCaseChars[] = $this->lexer->token->value;
}
}
return $upperCaseChars;
}
}
$upperCaseCharacterExtractor = new UpperCaseCharacterExtracter(new CharacterTypeLexer());
$upperCaseCharacters = $upperCaseCharacterExtractor->getUpperCaseCharacters('1aBcdEfgHiJ12');
print_r($upperCaseCharacters);
The variable ``$upperCaseCharacters`` contains all of the upper case
characters:
.. code-block:: php
Array
(
[0] => B
[1] => E
[2] => H
[3] => J
)
This is a simple example but it should demonstrate the low level API
that can be used to build more complex parsers.
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