;; 3-1.scm
;;
;; An accumulator is a procedure that is called repeatedly with a
;; single numeric argument and accumulates its arguments into a
;; sum. Each time it is called, it returns the currently accumulated
;; sum. Write a procedure make-accumulator that gen- erates
;; accumulators, each maintaining an indepen- dent sum. The input to
;; make-accumulator should specify the initial value of the sum; for example
;;   (define A (make-accumulator 5)) (A 10)
;;   15
;;   (A 10)
;;   25
;; --------------
;;
;; We did this together in class on Oct 21.
;;
;; $ scheme 3-1.scm
;; (define a1 (make-accumulator 10))
;; (a1 5) is 15.
;; (a1 5) is 20.
;;

(define (make-accumulator starting-amount)
  ;; return a function which
  ;; lets us add new amounts and
  ;; returns the new amount
  (lambda (amount)
    (set! starting-amount (+ amount starting-amount))
    starting-amount))

(define a1 (make-accumulator 10))
(printf "(define a1 (make-accumulator 10))\n")
(printf "(a1 5) is ~s.\n" (a1 5))
(printf "(a1 5) is ~s.\n" (a1 5))