Two Box Implementations

bob_and_alice.scm

#lang racket
 
(define (make-bob-box x y w h)
  (attach-tag 'bob-box (cons (cons x y) (cons w h))))
 
(define (bob-width box)
 (car (cdr (box))))

(define (bob-height box)
  (cdr (cdr (box))))

(define (make-alice-box x1 y1 x2 y2)
  (cons (cons x1 y1) (cons x2 y2)))

(define (alice-width box)
  (abs (- (car (cdr (box))
          (car (car (box)))))

(define (alice-height box)
  (abs (- (cdr (cdr (box))
          (cdr (car (box)))))

(define (alice-area box)
    (* (alice-width box)
       (alice-height box)))

(define a (make-alice-box 1 2 3 4))
(define b (make-bob-box 1 2 3 4))

(alice-area a) ;--> 4
(bob-area b)   ;--> 12