public function parseInputStreamWithBacktracking(InputStreamInterface $input, ExpressionResultInterface $previous_result = null)
{
if ($previous_result !== null) {
return null;
}
$string = $input->getRemainingString();
$result = $this->string_parser->parse($string);
if ($result === null) {
$input->move(-strlen($string));
return null;
}
$input->move($result->getLength() - strlen($string));
return $result;
}
