List where integer is expected coming out of function (Racket)

Question

I'm trying to set a value for a point in a multidimensional array using:

(vector-set! (vector-ref array (car xy)) (cadr xy) step_count)

But I'm getting this error:

vector-ref: contract violation
  expected: exact-nonnegative-integer?
  given: '(- (car xy) 1)
  argument position: 2nd
  other arguments...:
   '#(#(1 0 0 0 0) #(0 0 0 0 0) #(0 0 0 0 0) #(0 0 0 0 0) #(0 0 0 0 0))
   ;the value 1 at position (0,0) was set before by a similar line of code

xy values are generated by a separate function

I think my (car xy) is coming out of that function as a list. How do I stop this from happening?

Thanks for reading everyone!

Answer 1

Your list invocations are wrong. You should use, for example, something like this:

(cons (list (+ (car xy) 2) (- (cadr xy) 1)) successors)