#lang sicp
(define (print-point p)
  (newline)
  (display "(")
  (display (x-point p))
  (display ",")
  (display (y-point p))
  (display ")"))
(define (make-segment a b) (cons a b))
(define (start-segment seg) (car seg))
(define (end-segment seg) (cdr seg))
(define (make-point x y) (cons x y))
(define (x-point pt) (car pt))
(define (y-point pt) (cdr pt))
(define (midpoint-segment seg)
  (let ((x1 (x-point (start-segment seg)))
        (y1 (y-point (start-segment seg)))
        (x2 (x-point (end-segment seg)))
        (y2 (y-point (end-segment seg))))
        (make-point (/ (+ x1 x2) 2) (/ (+ y1 y2) 2))))

(print-point (midpoint-segment (make-segment 
                                  (make-point 0 0) 
                                  (make-point 3 3))))