;; ------------------------------------------------------------------
;; The Program Counter

(define PC (box 0))

(define get-pc
  (lambda () (unbox PC)))

(define set-pc!
  (lambda (addr)
    (set-box! PC addr)))

(define get&inc-pc
  (lambda ()
    (local ((define current (get-pc)))
      (set-pc! (add1 current))
      current)))