; a snake is 
; - symbol name
; - number weight
; - symbol food
(define-struct snake (name weight food))

;skinny-snake?: snake -> boolean
; returns true if snake is less than 10 pounds
;( ... (snake-name s) ...
; ... (snake-weight s) ...
; ... (snake-food s) ...)
(define (skinny-snake? s)
(<  (snake-weight s) 10))

(check-expect (skinny-snake? (make-snake 'frank 15 'donuts)) false)

; a dillo is
; - number weight
; - boolean dead
(define-struct dillo (weight dead))

; run-over-with-car: dillo -> dillo
; sets dead in dillo to true
; template:
; ( ... (dillo-weight d) ... 
; ...(dillo-dead d))...)
(define (run-over-with-car d) (
            make-dillo (dillo-weight d) true))

(check-expect (run-over-with-car (make-dillo 15 false)) (make-dillo 15 true))

; an ant is:
; - number weight
; - posn loc
(define-struct ant (weight loc))

; ant-at-home: ant -> boolean
; returns true if ant is at (0,0) and false
; otherwise
; template:
; (... ( ant-weight a) ... (ant-loc a) ...)
(define (ant-at-home a) 
                         (at-zero? (ant-loc a)))

(check-expect (ant-at-home (make-ant 0.01 (make-posn 0 0))) true)
(check-expect (ant-at-home (make-ant 0.01 (make-posn -1 1))) false)

; at-zero? : posn -> boolean
; returns if posn is (0,0)
; (... (posn-x p) ... 
; ... (posn-y p) ...)
(define (at-zero? p) 
        (and 
                (= (posn-x p) 0)
               (= (posn-y p) 0)       ))

(check-expect (at-zero? (make-posn 0 0)) true)
(check-expect (at-zero? (make-posn 0 1)) false)