Recursive Atom Counter in Scheme

Question

I need to come up with a scheme function that counts the occurence of an atom within a list. I successfully implemented a simple version but it only works with non-nested lists:

(define (foo x atom)
    (cond ((null? x) 0)
          ((eqv? (car x) atom) (+ 1 (count (cdr x) atom)))
          (else (count (cdr x) atom))))

I then attempted a nested-list version of it. However, I recieve the error:

argument of wrong type [car]

(car *whatever variable in list*)

The code is as follows:

(define (foo x atom)
  (cond
   ((null? x) 0)
   ((not (list? (car x)))
    (cond
     ((eqv? (car x) atom) (+ 1 (foo (cdr x) atom)))
     (else (foo (cdr x) atom))))
   (else (+ (foo (car x) atom) (foo (cdr x) atom)))))

It fails when I pass aa list such as:

(foo '(1 2 3 1 1 4 1) 1)

Answer 1

Example of count recursively:

(define (count k lst)
  (if (null? lst)
      0
      (if (= k (car lst))
       (+ 1 (count k (cdr lst)))
        (count k (cdr lst)))))

(count 2 '(2 3 4 4 4 5 5 3 2))
> 2
(count 4 '(2 3 4 4 4 5 5 3 2))
> 4

Explanation: if k exists in car (first), add 1 and check cdr (rest)...