;; 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-lambda-reader.ss" "lang")((modname quiz-review) (read-case-sensitive #t) (teachpacks ((lib "universe.ss" "teachpack" "2htdp") (lib "image.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "universe.ss" "teachpack" "2htdp") (lib "image.ss" "teachpack" "htdp")))))
;; squares list-of-numbers -> list-of-numbers
(check-expect (squares (list 2 3 4)) (list 4 9 16))

(define (squares alon)
  (map square alon))

;; square: number -> number
(define (square num)
  (* num num))

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;; first-quandrant list-of-posn -> list-of-posn
;; returns a list of positions in the first quadrant
(check-expect (first-quadrant (list (make-posn 1 3)
                                    (make-posn -1 3))) 
              (list (make-posn 1 3)))

(define (first-quadrant alop)
  (filter in-first? alop))

;; in-first? posn -> boolean
(define (in-first? aposn)
  (and (> (posn-x aposn) 0) 
       (> (posn-y aposn) 0)))

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;; intersection list-of-numbers list-of-numbers -> list-of-numbers
;; returns a list of all numbers in both the input lists
(define (intersection alon1 alon2)
  (filter (lambda (num)
            (in-list? num alon2))
          alon1))

(check-expect (intersection (list 2 4 6)
                            (list 2 3 9))
              (list 2))

;; in-list? number list-of-numbers -> boolean
(define (in-list? num alon)
  (cond [(empty? alon) false]
        [else (or (= (first alon) num)
                  (in-list? num (rest alon)))]))

(check-expect (in-list? 3 (list 2 3 6 6)) true)
(check-expect (in-list? 4 (list 2 3 6 6)) false)

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(define WS0 (make-posn 0 0))
(define WINDOW (empty-scene 800 400))
(define PLANE-IMAGE (text ">>" 20 "black"))

(define (render ws)
  (place-image PLANE-IMAGE (posn-x ws) (posn-y ws) WINDOW))

(define (go-down ws)
  (make-posn (+ (posn-x ws) 2) (+ (posn-y ws) 1)))

(define (landed? ws)
  (and (= (posn-x ws) 800)
       (= (posn-y ws) 400)))

;; Not needed -- just for fun
(define (last-scene ws)
  (place-image (text "ALL DONE!" 40 "black") 300 150 WINDOW))

(big-bang WS0
          (to-draw render)
          (on-tick go-down)
          (stop-when landed? last-scene))