simple-counter-a01-3TL4

;; Enhanced version

;; Simple Counter
(define-data-var tally uint u0)

(define-read-only (get-tally)
  (var-get tally)
)

(define-public (increment)
  (ok (var-set tally (+ (var-get tally) u1)))
)

(define-public (decrement)
  (begin
    (asserts! (> (var-get tally) u0) (err u1))
    (ok (var-set tally (- (var-get tally) u1)))
  )
)

(define-public (add (amount uint))
  (ok (var-set tally (+ (var-get tally) amount)))
)