anchor.diff:  ;;;>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
   
   (define (main script opts)
  -  (letn ((light-level (first opts))
  -         (int-level (integer light-level)))
  -    (cond
  -      ((light-value? int-level) (set-level light-level))
  -      ('true (display-bad-value light-level script))))
  +  (if (empty? opts)
  +    (get-brightness)
  +    (letn ((cmd-or-value (first opts))
  +           (int-level (integer cmd-or-value)))
  +      (cond
  +        ((= cmd-or-value "inc") (increment-brightness))
  +        ((= cmd-or-value "dec") (decrement-brightness))
  +        ((light-value? int-level) (set-level light-level))
  +        ('true (display-bad-value light-level script)))))
     (exit))
   
   ;;;>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
  
positive.code: ;;;>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
  
  (define (usage script)
    (letn ((base-template "%s %-10s %s")
           (opt-template (append "\t -" base-template)))
      (println)
      (println version-string)
      (println)
  
negative.code:        (>= value 1)
         (<= value 100)))
  
  (define (get-brightness)
    (! "xbacklight -get"))
  
  (define (set-level value)
    (! (format "xbacklight -set %s" value)))
  
  (define (increment-brightness)
    (! "xbacklight -inc 10"))
  
  (define (decrement-brightness)
    (! "xbacklight -dec 10"))
  
  (define (display-bad-value level script)
    (print (format "\nERROR: the provided value '%s' is not valid " level))
  