(defun callback (input output)
  (setf (gethash 'bar output)
        (mapcar #'- (gethash 'foo input))))

(defvar *petri-net-1*
  (make-petri-net '(foo bar)
    (list (make-transition 'foo 'bar #'callback))))

(defvar *petri-net-2*
  (petri-net () (foo -> #'callback -> bar)))

(defun do-test (petri-net input-bag input output-bag output)
  (map nil (curry #'bag-insert (bag petri-net input-bag)) input)
  (funcall petri-net)
  (let ((contents (bag-contents (bag petri-net output-bag))))
    (is (set-equal (coerce output 'list) (coerce contents 'list)))))

(defun test-petri-net ()
  (let ((input #(0 1 2 3 4 5 6 7 8 9))
        (output #(0 -1 -2 -3 -4 -5 -6 -7 -8 -9))))
  (do-test *petri-net-1*
           'foo input
           'bar output)
  (do-test *petri-net-2*
           'foo input
           'bar output))