class Rot13
{
  static Str rot13 (Str input)
  {
    Str result := ""
    input.each |Int c|
    {
      if ((c.lower >= 'a') && (c.lower <= 'm'))
        result += (c+13).toChar
      else if ((c.lower >= 'n') && (c.lower <= 'z'))
        result += (c-13).toChar
      else
        result += c.toChar
    }
    return result
  }

  public static Void main (Str[] args)
  {
    if (args.size == 1)
    { // process each line of given file
      Str filename := args[0]
      File(filename.toUri).eachLine |Str line|
      {
        echo (rot13(line))
      }
    }
    else
    {
      echo ("Test:")
      Str text := "abcstuABCSTU123!+-"
      echo ("Text $text becomes ${rot13(text)}")
    }
  }
}