;;;; Under Creative Commons Attribution-ShareAlike 4.0
;;;; International. See
;;;; <https://creativecommons.org/licenses/by-sa/4.0/>.

(define-module (net ricketyspace sicp two seven)
  #:export (make-interval
            lower-bound
            upper-bound
            add-interval))

(define (make-interval a b) (cons a b))

(define (lower-bound x) (car x))
(define (upper-bound x) (cdr x))

(define (add-interval x y)
  (make-interval (+ (lower-bound x) (lower-bound y))
                 (+ (upper-bound x) (upper-bound y))))