SICP Exercise 2.48

Question

A directed line segment in the plane can be represented as a pair of vectors – the vector running from the origin to the start-point of the segment, and the vector running from the origin to the end-point of the segment. Use your vector representation from Exercise 2.46 to define a representation for segments with a constructor make-segment and selectors start-segment and end-segment.

Answer

(define (make-segment seg-start seg-end)
  (cons seg-start seg-end))

(define (start-segment s)
  (car s))

(define (end-segment s)
  (cdr s))