Exercise 2.2. Consider the problem of representing line segments in a plane. Each segment is represented as a pair of points: a starting point and an ending point. Define a constructor
make-segment and selectors
end-segment that define the representation of segments in terms of points. Furthermore, a point can be represented as a pair of numbers: the
x coordinate and the
y coordinate. Accordingly, specify a constructor
make-point and selectors
y-point that define this representation. Finally, using your selectors and constructors, define a procedure
midpoint-segment that takes a line segment as argument and returns its midpoint (the point whose coordinates are the average of the coordinates of the endpoints). To try your procedures, you’ll need a way to print points:
(define (print-point p) (newline) (display "(") (display (x-point p)) (display ",") (display (y-point p)) (display ")"))
<mode nostalgia on> quando ero piccolo cose simili ne ho fatte parecchie, sigh 😊
<mode nostalgia off>. OK, vado.
;; point (define (make-point x y) (cons x y)) (define (x-point point) (car point)) (define (y-point point) (cdr point)) ;; segment (define (make-segment p1 p2) (list p1 p2)) (define (start-segment segment) (car segment)) (define (end-segment segment) (car (cdr segment))) ;; midpoint (define (midpoint segment) (cons (/ ( + (car (start-segment segment)) (car (end-segment segment))) 2) (/ (+ (cdr (start-segment segment)) (cdr (end-segment segment))) 2))) ;; print-point (define (print-point p) (newline) (display "(") (display (x-point p)) (display ",") (display (y-point p)) (display ")"))
Solo io ho usato la procedura
list, ma mi sembra che sia OK.