(import scheme (chicken base) interfaces)

(interface counter
  (define (counter-new))
  (define (counter-inc c))
  (define (counter-get c)))

(define simple-counter
  (implementation
    counter
    (define (counter-new) 0)
    (define counter-inc add1)
    (define counter-get identity)))

(let ((c1 ((counter-new simple-counter))))
  (print ((counter-get simple-counter) c1))     
  (let ((c2 ((counter-inc simple-counter) c1)))
    (print ((counter-get simple-counter) c2))))