(define choices
  '(("start window system" "startx")
    ("uitloggen" "exec logout")
    ("computer uitzetten" "exec poweroff")))

(define (print-menu)
  (print "\n--[ Menu ]--\n")
  (let1 num 1
    (dolist (entry choices)
      (format #t "~d - ~a\n" num (car entry))
      (inc! num))))

(define (read-choice)
  (format #t "\nkeuze: ")
  (flush)
  (let1 choice (read)
    (if (and (number? choice)
             (> choice 0)
             (<= choice (length choices)))
        choice
        (begin
          (format #t "\n*** Oeps: keuze '~a' bestaat niet.\n" choice)
          (read-choice)))))

(define (menu)
  (print-menu)
  (let* ((choice (read-choice))
         (command (cadr (list-ref choices (- choice 1)))))
    (print "command: " command)
    (menu)))

(define (main args)
  (print args)
  (menu))