#lang sicp

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

; top-left point, bottom-right point representation
(define (tlbr-rect a b)
  (cons 'tlbr (cons a b)))

; center point, width, height representation
(define (cpwh-rect p w h)
  (cons 'cpwh
        (cons p
              (cons w h))))

(define (height rect)
  (cond ((eq? 'cpwh (car rect)) (cdddr rect))
        (else (abs (- (y-point (cadr rect))
                      (y-point (cddr rect)))))))


(define (width rect)
  (cond ((eq? 'cpwh (car rect)) (caddr rect))
        (else (abs (- (x-point (cadr rect))
                      (x-point (cddr rect)))))))

(define (perimeter rect)
  (* 2 (+ (width rect) (height rect))))
(define (area rect)
  (* (width rect) (height rect)))