(defun discrete-gen (names)
  "Return a random sample from list names"
  (elt names (random (length names))))

(defstruct dvg
  generator
  serializer)

(defmethod call ((dvg dvg))
  (funcall (dvg-generator dvg)))
(defmethod serialize ((dvg dvg) stream)
  (funcall (dvg-serializer dvg) stream))
(defun deserialize (stream)
  (let ((*read-eval* t)) (read stream)))

(defun discrete-variable-generator (names)
  (make-dvg
   :generator (lambda () (discrete-gen names))
   :serializer (lambda (stream) (format stream "#.(discrete-variable-generator ~S)" names))))


(let ((dvg (discrete-variable-generator #("foo" "bar" "baz"))))
  (call (with-input-from-string (stream  (with-output-to-string (stream) (serialize dvg stream)))
          (deserialize stream))))
;; --> "foo"