;; 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-intermediate-reader.ss" "lang")((modname lec16) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
;; includes? : X list-of-X -> bool
(define (includes? who los)
  (cond
    [(empty? los) false]
    [(cons? los)
     (or (equal? (first los) who)
         (includes? who (rest los)))]))
;; `includes?' is actually built in as `member'

(check-expect (includes? (make-posn 1 2) empty)
              false)
(check-expect (includes? (make-posn 1 2) (list
                                          (make-posn 7 8)
                                          (make-posn 1 2)))
              true)

;; got-milk? : list-of-symbol -> bool
(define (got-milk? los)
  (includes? 'milk los))

(check-expect (got-milk? empty) false)
(check-expect (got-milk? '(milk)) true)
(check-expect (got-milk? '(eggs bacon)) false)
(check-expect (got-milk? '(eggs milk bacon)) true)

;; includes-person? : string list-of-string -> bool
(define (includes-person? who los)
  (includes? who los))

(check-expect (includes-person? "Mario" empty) false)
(check-expect (includes-person? "Mario" '("Mario")) true)
(check-expect (includes-person? "Mario" '("Luigi" "Bowser")) false)
(check-expect (includes-person? "Mario" '("Luigi" "Mario" "Bowser")) true)