(define-struct boa (name length food))
;; a Boa is a (make-boa String Natural String)
;; interp:  a boa constrictor, where
;;   name is the boa's name
;;   length is its length (in inches)
;;   food the the boa's favorite food

;; examples
(define MARY (make-boa "Mary" 37 "ferns"))


(define-struct dillo (length dead?))
;; A Dillo is a (make-dillo Natural Boolean)
;; interp:  an armadillo where
;;   length is the dillo's length (in inches)
;;   dead? is true if the dillo is dead

(make-dillo 12 false)
(define MAX (make-dillo 14 true))


;; provide a data definition for a tiger that has a name, a length,
;; and a product that it sells.  A product is comprised of the item,
;; and the manufacturer

(define-struct product (item manufacturer))
;; a Product is a (make-product String String)
;; interp: a product where
;;  item is the name of the item
;;  manufacturer is the manufacturer

(make-product "Frosted Flakes" "Kelloggs")

;;; fcn-for-product:  Product ->
;;;
;(define (fcn-for-product a-prod)
;  (... (product-item a-prod)
;       (product-manufacturer a-prod)))



(define-struct tiger (name length sells))
;; a Tiger is a (make-tiger String Natural Product)
;; interp:  a tiger where
;;  name is the tiger's name
;; length is its length (in inches)
;; sells is a product that the tiger sells

(make-tiger "Tony" 72 (make-product "Frosted Flakes" "Kelloggs"))

;;; fcn-for-tiger:  Tiger ->
;;;
;(define (fcn-for-tiger a-tiger)
;  (...  (tiger-name a-tiger)
;        (tiger-length a-tiger)
;        (fcn-for-product (tiger-sells a-tiger))))




;; an Animal is one of
;;  Boa
;;  Dillo
;;  Tiger

;;; fcn-for-animal:  Animal ->
;;;
;(define (fcn-for-animal an-ani)
;  (cond [(boa? an-ani)  (... (boa-name an-ani)
;                             (boa-length an-ani)
;                             (boa-food an-ani))]
;        [(dillo? an-ani) (... (dillo-length an-ani)
;                              (dillo-dead? an-ani))]
;        [(tiger? an-ani) (fcn-for-tiger an-ani)]))
;



;; sells-gas?:  Animal -> Boolean
;; consumes an animal and produces true if the item that the animal sells is
;; gas.  If the animal doesn't sell a product, the function returns false
(define (sells-gas? an-ani)
  (cond [(boa? an-ani)  false]
        [(dillo? an-ani) false]
        [(tiger? an-ani) (tiger-sells-gas? an-ani)]))


;; test
(check-expect (sells-gas? (make-boa "Slim" 19 "pickles")) false)
(check-expect (sells-gas? (make-tiger "Tony" 70 (make-product "Frosted Flakes" "Kelloggs"))) false)

;; tiger-sells-gas?: Tiger -> Boolean
;; consumes a tiger and produces true if the item the tiger sells is gas
(define (tiger-sells-gas? a-tiger)
  (...  
        
        (item-is-gas? (tiger-sells a-tiger))))

;; item-is-gas?:  Product -> Boolean
;; produces true if the item in the product is gas
(define (fcn-for-product a-prod)
  (... (product-item a-prod)
       (product-manufacturer a-prod)))