(library
  (utils)
  (export inc!
          dec!)
  (import (rnrs))

  (define-syntax inc!
    (syntax-rules ()
      ((_ v) (set! v (+ 1 v)))
      ((_ v n) (set! v (+ n v)))))

  (define-syntax dec!
    (syntax-rules ()
      ((_ v) (set! v (- v 1)))
      ((_ v n) (set! v (- v n)))))
  )