; Note: you need to be in "Intermediate Student with Lambda" or "Advanced Student" language,
; and you need the "gui.ss" teachpack loaded.

; can-vote? : number => boolean
(define (can-vote? age)
  (>= age 18))
"Examples of can-vote?:"
(can-vote? 17) "should be false"
(can-vote? 18) "should be true"
(can-vote? 97) "should be true"

; voting-message : string => string
(define (voting-message text)
  (local [(define age (string->number text))]
    (cond [(not (number? age))
           (format "I don't understand ~s; the age must be a number." text)]
          [(>= age 18) (format "~s is old enough to vote.  Congratulations!" age)]
          [(< age 18) (format "~s is NOT old enough to vote yet." age)])))
"Examples of voting-message:"
(voting-message "18") "should be \"18 is old enough to vote.  Congratulations!\""
(voting-message "17") "should be \"17 is NOT old enough to vote.\""
(voting-message "p3n890") "should be \"I don't understand \"p3n890\"; the age must be a number.\""

(define age-box (make-text "How old are you?"))
(define ANSWER-LENGTH 90)
(define answer (make-message (make-string ANSWER-LENGTH #\space)))

(define do-it-button
  (make-button "Go ahead!"
               (lambda (event)
                 (draw-message answer (voting-message (text-contents age-box))))))
(define quit-button (make-button "Quit" hide-window))

; hello: dummy -> nothing
; Puts up a window.  Whenever the "Go ahead" button is clicked, checks the
; contents of the age-box, and puts an appropriate message in "answer".
(define (hello dummy)
  (create-window (list (list age-box do-it-button)
                       (list answer)
                       (list quit-button))))