(define-syntax inc!
  (syntax-rules ()
    ((_ variable)
     (set! variable (+ variable 1)))
    ((_ variable value)
     (set! variable (+ variable value)))))

(define-syntax dec!
  (syntax-rules ()
    ((_ variable)
     (set! variable (- variable 1)))
    ((_ variable value)
     (set! variable (- variable value)))))

(define-syntax while
  (syntax-rules ()
    ((_ condition body)
     (letrec ((loop
               (lambda () (if condition
                         (begin
                           body
                           (loop))))))
       (loop)))))

(define (append-to-list L element)
  (append L (list element)))

(define-syntax append-to-list!
  (syntax-rules ()
    ((_ list element)
     (set! list (append-to-list list element)))))