total := 0.0
{() -> {
  ("Total: ", total, ". Type a number to change.").concat.println
  ().read_line.trim.parse_float.try((
    n -> &total = (total, n).sum,
    // not a number, so return a 1-tuple to break from the loop
    () -> (())
  ))
}}.loop
"Goodbye.".println