2.2.scm

(define (print-point p)
  (newline)
  (display "(")
  (display (x-point p))
  (display ",")
  (display (y-point p))
  (display ")"))

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

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

(define (midpoint-segment line)
(let ((start-point (start-segment line))
(end-point (end-segment line)))
(make-point (average (x-point start-point) (x-point end-point))
(average (y-point start-point) (y-point end-point)))))