(require 2htdp/image)
;; SPD2-Design-Quiz-1.rkt


;; ======================================================================
;; Constants
(define COOKIES .)

;; ======================================================================
;; Data Definitions

;; Natural is one of:
;; - 0
;; - (add1 Natural)
;; interp. a natural number
(define N0 0) ;0
(define N1 (add1 N0)) ;1
(define N2 (add1 N1)) ;2

#;
(define (fn-for-natural n)
(cond [(zero? n) (…)]
[else
(… n ; n is added because it’s often useful
(fn-for-natural (sub1 n)))]))

;; Template rules used:
;; - one-of: two cases
;; - atomic distinct: 0
;; - compound: 2 fields
;; - self-reference: (sub1 n) is Natural




; PROBLEM 1:
;
; Complete the design of a function called pyramid that takes a natural
; number n and an image, and constructs an n-tall, n-wide pyramid of
; copies of that image.
;
; For instance, a 3-wide pyramid of cookies would look like this:
;
; .


;; Natural Image -> Image
;; produce an n-wide pyramid of the given image
(check-expect (pyramid 0 COOKIES) empty-image)
(check-expect (pyramid 1 COOKIES) COOKIES)
(check-expect (pyramid 3 COOKIES)
(above COOKIES
(beside COOKIES COOKIES)
(beside COOKIES COOKIES COOKIES)))

;(define (pyramid n i) empty-image) ; stub

(define (pyramid n img)
(cond [(zero? n) empty-image]
[else (above (pyramid (sub1 n) img)
(pyramid-row n img))]))

(define (pyramid-row n img)
(cond [(zero? n) empty-image]
[else (beside img (pyramid-row (sub1 n) img))]))

; Problem 2:
; Consider a test tube filled with solid blobs and bubbles. Over time the
; solids sink to the bottom of the test tube, and as a consequence the bubbles
; percolate to the top. Let’s capture this idea in BSL.
;
; Complete the design of a function that takes a list of blobs and sinks each
; solid blob by one. It’s okay to assume that a solid blob sinks past any
; neighbor just below it.
;
; To assist you, we supply the relevant data definitions.


;; Blob is one of:
;; - “solid”
;; - “bubble”
;; interp. a gelatinous blob, either a solid or a bubble
;; Examples are redundant for enumerations
#;
(define (fn-for-blob b)
(cond [(string=? b “solid”) (…)]
[(string=? b “bubble”) (…)]))

;; Template rules used:
;; - one-of: 2 cases
;; - atomic distinct: “solid”
;; - atomic distinct: “bubble”


;; ListOfBlob is one of:
;; - empty
;; - (cons Blob ListOfBlob)
;; interp. a sequence of blobs in a test tube, listed from top to bottom.
(define LOB0 empty) ; empty test tube
(define LOB2 (cons “solid” (cons “bubble” empty))) ; solid blob above a bubble

#;
(define (fn-for-lob lob)
(cond [(empty? lob) (…)]
[else
(… (fn-for-blob (first lob))
(fn-for-lob (rest lob)))]))

;; Template rules used
;; - one-of: 2 cases
;; - atomic distinct: empty
;; - compound: 2 fields
;; - reference: (first lob) is Blob
;; - self-reference: (rest lob) is ListOfBlob

;; ListOfBlob -> ListOfBlob
;; produce a list of blobs that sinks the given solid blobs by one

(check-expect (sink empty) empty)
(check-expect (sink (cons “bubble” (cons “solid” (cons “bubble” empty))))
(cons “bubble” (cons “bubble” (cons “solid” empty))))
(check-expect (sink (cons “solid” (cons “solid” (cons “bubble” empty))))
(cons “bubble” (cons “solid” (cons “solid” empty))))
(check-expect (sink (cons “solid” (cons “bubble” (cons “bubble” empty))))
(cons “bubble” (cons “solid” (cons “bubble” empty))))
(check-expect (sink (cons “solid” (cons “bubble” (cons “solid” empty))))
(cons “bubble” (cons “solid” (cons “solid” empty))))
(check-expect (sink (cons “bubble” (cons “solid” (cons “solid” empty))))
(cons “bubble” (cons “solid” (cons “solid” empty))))
(check-expect (sink (cons “solid”
(cons “solid”
(cons “bubble” (cons “bubble” empty)))))
(cons “bubble” (cons “solid”
(cons “solid” (cons “bubble” empty)))))
;(define (sink lob) empty) ; stub

(define (sink lob)
(cond [(empty? lob) lob] ; base case: empty list
[(string=? (first lob) “solid”)
(append (sink (rest lob)) (list “solid”))]
[else (cons (first lob) (sink (rest lob)))]))

Ran 10 tests.
2 of the 10 tests failed.

Check failures:
Actual value (list “bubble” “bubble” “solid”) differs from (list “bubble” “solid” “bubble”), the expected value.
in Naturals-and-Helpers-Design-Quiz (1).rkt, line 105, column 0
Actual value (list “bubble” “bubble” “solid” “solid”) differs from (list “bubble” “solid” “solid” “bubble”), the expected value.
in Naturals-and-Helpers-Design-Quiz (1).rkt, line 111, column 0