(define-struct cat (name age high?))

(define hyde (make-cat 'bartok 21 true))
(define imposter (make-cat 'bartok 21 true))
(define jekyll hyde)


;; age-cat!: cat --> (void)
;;
(define (age-cat! meowser)
  (set-cat-age! meowser (add1 (cat-age meowser))))

hyde
jekyll
imposter
(age-cat! hyde)
hyde
jekyll
imposter

;;;;;; Review syntax, semantics, pragmatics.
;; Note the convention of "!" -- side-effects!


(error 'to-do
       "To continue, go back and adapt the 'cat' structure to include a \"buddy\" field.")


(list jekyll
      hyde
      imposter
      jekyll
      (make-cat 'morris 102 false (make-cat 'cleo 22 false imposter)))

;; (Note: set-first!, set-rest!)


;;;;;; A pragmatic:
;;
(define-struct posn (x y))

(define-struct Rectangle (nw wide high))
(define-struct Circle    (center radius))

(define origin (make-posn 0 0))

(define blocko (make-Rectangle origin 20 30))
(define blobbo (make-Circle origin 10))

;; Two ways to move blocko's nw corner to (90,90):
;;
(set-posn-x! (Rectangle-nw blocko) 90)
(setRectangle-nw! blocko (make-posn 90 90))





;;;;;; Structures within structures.

(define cat2 (make-cat 'freddy-kruger 92 false hyde))
(set-cat-buddy! hyde cat2)


;; Go back and modify the function age-cat!,
;; so that older cats aren't still high on catnip.