get 7 not (7) out of the list?

Question

Here's my code:

  (define step1_list1 '(1 3 (5 7) 9))

  (car (cdr (cdr (step1_list1))))


   (define step1_list2 '((7)))

   (car (step1_list2))


   (define step1_list3 '(1 (2 (3 (4 (5 (6 7)))))))

   (car (cdr (cdr (cdr (cdr (cdr step1_list3))))))

  ))

Running this code causes an error:

(1 3 (5 7) 9) is not applicable

What is the problem?

Answer 1

Start small.

(define mylist '(1 2 3))

(display mylist)

(display (car mylist))

(display (car (mylist)))

Run each of those in turn, and see what you get at each step. Once you understand why you get the output you do, then you should be able to fix the code in your question.

Answer 2

In Scheme, (non-quoted) parentheses mean function application. So (car (step1_list2)) tries to execute step1_list2 as a procedure (and then take the car of the result). Instead, you want:

(car step1_list2)