How can you put structure objects into a list?

Question

#lang Scheme

(define-struct storeItem (id des cost))

(define redApple (make-storeItem 0 "red delicious apple" 1.99))
(define chickenLeg (make-storeItem 1 "boned chicken" 2.99))
(define porkLoin (make-storeItem 2 "processed pork" 4.99))
(define milkD (make-storeItem 3 "vitamin d milk" 3.99))
(define baguetteBread (make-storeItem 4 "french bread" 0.99))
(define orangeJuice (make-storeItem 5 "fruit juice drink)" 1.49))
(define beanCan (make-storeItem 6 "beans in a can" 2.49))

(define masterList '(redApple chickenLeg porkLoin milkD baguetteBread 
   orangeJuice beanCan))

I am trying to get a list of objects from my structure and I am unsure of the correct syntax. Below is what I tired

(storeItem-des (car masterList)

I was expecting "red delicious apple"

But I get

storeItem-des: contract violation
expected: storeItem?
given: redApple

It seems like it is returning redApple, which seems correct. Where am I going wrong?

This problem is answered by [What is the difference between `quote` and `list`?](https://stackoverflow.com/questions/34984552/what-is-the-difference-between-quote-and-list) — Alex Knauth, Oct 14 '18 at 22:48

score 1 · Answer 1 · answered Oct 14 '18 at 21:33

1

You're creating a list of symbols, not storeItems.

'(x y z) is equivalent to (list 'x 'y 'z), not (list x y z). So if you want to create a list containing the values of the variables x, y and z, you need to use the latter.

answered Oct 14 '18 at 21:33

sepp2k

363,768
54
674
675

Ah thank you for that. application: not a procedure; expected a procedure that can be applied to arguments given: # arguments...: This is what I get whenever I change the list type. – Jonnyutah Oct 14 '18 at 21:34
@Jonnyutah For which code do you get that error message? – sepp2k Oct 14 '18 at 21:42
@Jonnyutah Did you write `(list redApple chickenLeg ...)`? – Barmar Oct 14 '18 at 21:42
@Jonnyutah It sounds like you forgot to put `list` at the beginning. – Barmar Oct 14 '18 at 21:42
@Barmar If I create (list 1 2 3) How am I navigating that list if there is no name for it? Thanks! – Jonnyutah Oct 14 '18 at 21:44
@Jonnyutah It's in the `masterList` variable. `(define masterList (list redApple chickenLeg ...))` – Barmar Oct 14 '18 at 21:47
@Barma Thank you! I was able to get it. I used (define masterList (list element0 element1....element n)) – Jonnyutah Oct 14 '18 at 21:47

How can you put structure objects into a list?

1 Answers1