;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname lec4) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
;; A snake is
;;   (make-snake sym num sym)

(define-struct snake (name weight food))

;; snake-skinny? : snake -> boolean
;;  To determine whether s is strictly less than 10 lbs
;(define (snake-skinny? s)
;  ... (snake-name s) ... (snake-weight s) ... (snake-food s)  ...)
(define (snake-skinny? s)
  (< (snake-weight s) 10))

(check-expect (snake-skinny? (make-snake 'Slinky 10 'rats))
              false)
(check-expect (snake-skinny? (make-snake 'Slimey 8 'grass))
              true)
(check-expect (snake-skinny? (make-snake 'Hefty 25 'cows))
              false)

;; feed-snake : snake -> snake
;;  To feed s 5 lbs of food
;(define (feed-snake s)
;  .... (snake-name s) ... (snake-weight s) ... (snake-food s) ...)
(define (feed-snake s)
  (make-snake (snake-name s) (+ 5 (snake-weight s)) (snake-food s)))

(check-expect (feed-snake (make-snake 'Slinky 10 'rats))
              (make-snake 'Slinky 15 'rats))
(check-expect (feed-snake (make-snake 'Slimey 8 'grass))
              (make-snake 'Slimey 13 'grass))

;; A dillo is
;;  (make-dillo num bool)
(define-struct dillo (weight alive?))

;; run-over-with-car : dillo -> dillo
;;  To (sadly) kill d
;(define (run-over-with-car d)
;  ...  (dillo-weight d) ...  (dillo-alive? d) ...)
(define (run-over-with-car d)
  (make-dillo (dillo-weight d) false))

(check-expect (run-over-with-car (make-dillo 2 true))
              (make-dillo 2 false))
(check-expect (run-over-with-car (make-dillo 8 false))
              (make-dillo 8 false))


;; feed-dillo : dillo -> dillo
;;    To feed d 2 lds of food, if d is alive?
;(define (feed-dillo d)
;  .... (dillo-weight d) .... (dillo-alive? d) ...)
(define (feed-dillo d)
  (cond
    [(dillo-alive? d) (make-dillo (+ 2 (dillo-weight d)) true)]
    [else d]))

(check-expect (feed-dillo (make-dillo 2 true))
              (make-dillo 4 true))
(check-expect (feed-dillo (make-dillo 2 false))
              (make-dillo 2 false))