public function tokenize($source, $name = null)
    {
        if (!$source instanceof Twig_Source) {
            @trigger_error(sprintf('Passing a string as the $source argument of %s() is deprecated since version 1.27. Pass a Twig_Source instance instead.', __METHOD__), E_USER_DEPRECATED);
            $source = new Twig_Source($source, $name);
        }

        if (null === $this->lexer) {
            $this->lexer = new Twig_Lexer($this);
        }

        return $this->lexer->tokenize($source);
    }