mers/examples/02_Calc_Sum.mers

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