CODEWITHSUNDEEP
schemestructureracket
BBladem83
BBladem83

Reputation: 623

Scheme (DrRacket) - Outputting an entire Structure

I'm fairly new to Scheme and I'm using DrRacket and I hope to get some much needed assistance.

I need to "combine" the four field values of my structure to make a single structure which you should be returning.

The four field values I am referring to are in the if statement of the code:

((auction-itemnum anentry)(auction-name anentry)(auction-currbid anentry)(auction-status anentry))

That of course does not work, as it won't let me run that.

This means my second if statement isn't going to work either, but if I can figure out the first one, then the second one will be clear.

The output I need is: (make-auction 50 "Bob" 100 "Open")

(at least for the second check-expect)

But figuring out the second check-expect will make the others work as well.

Here is my code:

(define-struct auction (itemnum name currbid status))

(define Auction1
  (make-auction 50 "Bob" 100 "Open"))

(define Auction2
  (make-auction 20 "Joe" 40 "Closed"))

;; Data Definition of an auction
;; An auction is a structure: (make-auction itemnum name currbid status)
;; interp. item number, name, current bid, and status, represented
;;         by a string

;; Signature: auctionbid: string number entry -> entry
;; Purpose: Consumes a bidder, a bid amount, and an auction entry
;;          then returns an entry
;; Tests:
(check-expect (auctionbid "Frank" 150 Auction1) (make-auction 50 "Frank" 150 "Open"))
(check-expect (auctionbid "Billy" 80 Auction1) (make-auction 50 "Bob" 100 "Open"))
(check-expect (auctionbid "Jenny" 50 Auction2) (make-auction 20 "Joe" 40 "Closed"))
;; Define:
(define (auctionbid aname bid anentry)
  (cond
    [(or (< bid (auction-currbid anentry)) (string=? "Closed" (auction-status anentry)))
     ((auction-itemnum anentry) (auction-name anentry)
      (auction-currbid anentry) (auction-status anentry))]
    [(> bid (auction-currbid anentry))
     ((auction-itemnum anentry)(aname)
      (bid)(auction-status anentry))]
     ))

Upvotes: 2

Views: 144

Answers (1)

Throw Away Account
Throw Away Account

Reputation: 2671

There's no reason in the world why you'd ever want a copy of an immutable struct. Just return the struct itself if you're not changing anything. Otherwise, you need to construct a new struct using "make-auction":

(define (auctionbid aname bid anentry)
  (cond
    [(or (< bid (auction-currbid anentry))
         (string=? "Closed" (auction-status anentry)))
     anentry]
    [(> bid (auction-currbid anentry))
     (make-auction (auction-itemnum anentry)
                   aname bid 
                   (auction-status anentry))]))

Upvotes: 2

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