問題2.47

(define (make-frame origin edge1 edge2)
  (list origin edge1 edge2))
(define (edge1-frame frame) (cadr frame))
(define (edge2-frame frame) (caddr frame))
(define (origin-frame frame) (car frame))

(define f1 (make-frame (cons 1 2) 1 2))
(edge1-frame f1)
;->1
(edge2-frame f1)
;->2
(origin-frame f1)
;->(1 . 2)


(define (make-frame origin edge1 edge2)
  (cons origin (cons edge1 edge2)))
(define (edge1-frame frame) (cadr frame))
(define (edge2-frame frame) (cddr frame))
(define (origin-frame frame) (car frame))

(define f1 (make-frame (cons 1 2) 1 2))
(edge1-frame f1)
;->1
(edge2-frame f1)
;->2
(origin-frame f1)
;->(1 . 2)