kb-light.scm

#!/usr/local/bin/csi -s

(use dbus)

(: main (-> string))
(define (main)
  (let* ((kb-light (make-context
                    #:bus system-bus
                    #:service 'org.freedesktop.UPower
                    #:interface 'org.freedesktop.UPower.KbdBacklight
                    #:path '/org/freedesktop/UPower/KbdBacklight))
         (argv (command-line-arguments))
         (up-down (when (not (null? argv)) (car argv)))
         (delta (cond ((equal? up-down "+") 17)
                      ((equal? up-down "-") -17)
                      (else 0)))
         (current (car (call kb-light "GetBrightness")))
         (maximum (car (call kb-light "GetMaxBrightness")))
         (new (max 0 (+ current delta))))
    (when (<= 0 new maximum)
      (call kb-light "SetBrightness" new))
    (format #t "~s~%" (inexact->exact
                       (round (* 100 (/ new maximum)))))))

(main)