private function getCalleeData($trace, $pos = 0) {
        $traceRow = isset($trace[$pos]) ? $trace[$pos] : end($trace);
        $file = isset($traceRow['file']) ? $traceRow['file'] : '[internal function]';
        $line = isset($traceRow['line']) ? '#' . $traceRow['line'] : '';
        $str = $file . " " . $line;
        return $str;
    }