public function format($operator, $value, &$states = [])
    {
        $defaults = [
            'schemas' => [],
            'aliases' => [],
            'schema' => null
        ];
        $states += $defaults;
        if (!isset($this->_formatters[$operator])) {
            throw new SqlException("Unexisting formatter `'{$operator}'`.");
        }
        $formatter = $this->_formatters[$operator];
        return $formatter($value, $states);
    }