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 andT_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-zA-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.