(define (find-closest-number goal numbers)
   (if (= 1 (length numbers))
       (car numbers)
       (if (< (abs (- goal (car numbers)))
              (abs (- goal 
                      (find-closest goal (cdr numbers)))))
           (car numbers)
           (find-closest goal (cdr numbers)))))

(define (find-closest goal lst comparator)
  (if (= 1 (length lst))
      (car numbers)
      (if (< (comparator goal (car lst))
             (comparator goal 
                         (find-closest goal (cdr lst) comparator)))
          (car lst)
          (find-closest goal (cdr lst) comparator))))

(define (find-closest-number2 goal numbers)
  (find-closest goal numbers (lambda (a b) (abs (- a b)))))