Match Patterns & Test Review

1. Question 1

   Q: Write the racket expression that applies a function named mix-otgether to the arguments “peanut-butter” and “pickles”.

   A: (mix-together “peanut-butter” “pickles”)

2. Question 2

   Q: Write two test cases(using check-equal?) for the threes-in-number function, that accepts an integer and returns the number of occurrences of the digit ’3’

   Too Lazy… Test

…

1. Question 4

   Answer

   A = {apple, pear, orange}

   B = {banana}

   AUB = {apple, pear, orange, banana}

   three elements that can be in the set for a choice of it being in or not.

   2³

   2*2*2 = 8

; takes in a list of number
; returns a list where all the
; numbers are doubled

; double all the numbers in the given list
(define (double[list: (Listof Real)]) : (Listof Real)
  (match lst
    ['() '()]
    [(cons f r) (cons (* f 2)) (double r)]))


(check-equal? (double '(1 2 3) '(2 4 6))
(check-equal? (double '()) '())
(check-equal? (double '(0 -5 102)) '(0 -10 204))

How Double Works

(double ’(10 20)) -> not empty so assigns f to 10 and r to 20

=(cons (* 2 10) (double ’(20))) -> form a cons with doubling 10 and calling double on ’(20)

=(cons 20 (double ’(20)))

=(cons 20(cons (* 2 20) (double ’())))

=(cons 20 (cons 40 (double ’())))

=(cons 20 (cons 40 ’()))

(define (func [lst : (listof Integer)])
  (match lst
    [(cons fst (cons scnd (cons thrd rst)))
     "There is exactly three elemnts in this list."]))

(define (func [lst : (listof Integer)])
  (match lst
    [(cons (? even? f) r) (format "first value is even: ~v" f)]
    [(cons fst (cons scnd (cons thrd rst)))
     "There is exactly three elemnts in this list."]))

Matches that fall off the end ERROR

• add an identifer, [(other) … ]