2 days ago

my attempt to do the exercises in sicp.

## Sunday, July 20, 2008

### sicp exercise 2.48

;; Exercise 2.48. 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.

(define (make-vect x y) (cons x y))

(define (xcor-vect vect) (car vect))

(define (ycor-vect vect) (cdr vect))

(define (add-vect vect1 vect2)

(let ((x1 (xcor-vect vect1)))

((x2 (xcor-vect vect2)))

((y1 (ycor-vect vect1)))

((y2 (ycor-vect vect2)))

(make-vect (+ x1 x2) (+ y1 y2))))

(define (sub-vect vect1 vect2)

(let ((x1 (xcor-vect vect1)))

((x2 (xcor-vect vect2)))

((y1 (ycor-vect vect1)))

((y2 (ycor-vect vect2)))

(make-vect (- x1 x2) (- y1 y2))))

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

(define (start-segment line-segment) (car line-segment))

(define (end-segment line-segment) (cdr line-segment))

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