2.2|

$ cd ~

SICP Exercise 2.2

(define (make-point x y) (cons x y))
(define (x-point p) (car p))
(define (y-point p) (cdr p))
(define (print-point p)
  (newline)
  (display "(")
  (display (x-point p))
  (display ",")
  (display (y-point p))
  (display ")"))

(define (make-segment start-point end-point)
  (cons start-point end-point))
(define (start-segment segment) (car segment))
(define (end-segment segment) (cdr segment))

(define (midpoint-segment segment)
  (define (average a b) (/ (+ a b) 2))
  (let ((a (start-segment segment))
        (b (end-segment segment)))
    (make-point (average (x-point a)
                         (x-point b))
                (average (y-point a)
                         (y-point b)))))