SICP 2.48

前に解いたような問題だな。相変わらず図形はなし。

(define make-vect cons)
(define xcor-vect car)
(define ycor-vect cdr)

(define (add-vect v1 v2)
  (make-vect (+ (xcor-vect v1) (xcor-vect v2))
             (+ (ycor-vect v1) (ycor-vect v2))))

(define make-segment cons)
(define start-segment car)
(define (end-segment s)
  (add-vect (start-segment s)
            (cdr s)))

; test
(define s (make-segment (make-vect 1 2) (make-vect 5 7)))
(start-segment s)
(end-segment s)