Doctrine LEFT mysql function

<?php
use Doctrine'ORM'Query'AST'Functions'FunctionNode;
use Doctrine'ORM'Query'Lexer;
/**
 * JsonbExistence ::= "LEFT('a', 'b')"
 *
 * This will be converted to: "LEFT('a', 'b')"
 *
 */
class LeftFunction extends FunctionNode
{
    public $column = null;
    public $regexp = null;
    public function parse('Doctrine'ORM'Query'Parser $parser)
    {
        $parser->match(Lexer::T_IDENTIFIER);
        $parser->match(Lexer::T_OPEN_PARENTHESIS);
        $this->column = $parser->ArithmeticPrimary();
        $parser->match(Lexer::T_COMMA);
        $this->regexp = $parser->ArithmeticPrimary();
        $parser->match(Lexer::T_CLOSE_PARENTHESIS);
    }
    public function getSql('Doctrine'ORM'Query'SqlWalker $sqlWalker)
    {
        return sprintf('LEFT(%s, %s)', $this->column->dispatch($sqlWalker), $this->regexp->dispatch($sqlWalker));
    }
}