SICP Ex 2.2: Make-segment

make-segment.scm

(define (make-point x y)(cons x y))
(define (x-point point)(car point))
(define (y-point point)(cdr point))

(define (make-segment pointa pointb)(cons pointa pointb))
(define (start-segment segment)(car segment))
(define (end-segment segment)(cdr segment))
(define (midpoint-segment segment)
  (make-point (/ (+ (x-point (start-segment segment))
                    (x-point (end-segment   segment))) 2)
              (/ (+ (y-point (start-segment segment))
                    (y-point (end-segment   segment))) 2)))


;; Testing ;;
(define a (make-point 1 2))
(define b (make-point 1 5))
(define seg (make-segment a b))
(display seg)
(newline)
(display (end-segment seg))
(newline)
(display (midpoint-segment seg))