(define (make-blah)
  (lambda ()
    (print "blah")))

(define (make-zooi)
  (lambda ()
    (print "zooi")))

;; how can do this ...

(define (zooi?)
  ;; ???
  )

(zooi? (make-blah)) ;; -> #f
(zooi? (make-zooi)) ;; -> #t