mers/examples/02_Calc_Sum.mers

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