<?^open Unix let st = stat "robots.txt" 
    let sz = float_of_int st.st_size ?>
<?let (amt, unit) = match arg "unit" with
      | Some "M" -> (.~(lift(sz /. 1048576.)), "M")
      | Some "k" -> (.~(lift(sz /. 1024.)), "k")
      | _          -> (sz, "") ?>
<?"%.1f%s" amt, unit ?>