#+SBCL (DECLAIM (SB-EXT:MUFFLE-CONDITIONS CL:STYLE-WARNING))
(let ((globals (make-hash-table)))
  (defun isa (name type)
    (setf (gethash name globals) 
          (make-instance type :name name)))
  (defmethod zap () (maphash #'(lambda (k v)  (declare (ignore k))
                                              (setf (cached-value v) nil))
                             globals))
  (defun one (s) 
    (gethash s globals (one-error s)))
)
(defun one-error (s)
  (error "no cached value for ~a" s))

(defclass cached ()
  ((name :accessor cached-name   :initarg :name :initform (gensym "cached"))
   (value :accessor cached-value :initarg :value :initform nil)))

(defmethod ! ((s null)   )  (error "missing cached value"))
(defmethod ! ((s symbol ))  (! (one s)))
(defmethod ! ((s string ))  (! (one s)))
(defmethod ! ((c cached))   (or (cached-value c) (setf (cached-value c) (? c))))
(defmethod ? ((c cached))   (format t "missing method"))

(defmethod ? ((o oneof))
  (let* ((l (all o))
         (n (length l)))
    (elt l (random n))))

(defclass ranged   (cached)  nil)
(defmethod ? ((r ranged))
  (+ (from r)  (*  (/ (random 1000) 1000) (- (to   r) (from r)))))
  
(defmethod from ((r ranged)) 0)
(defmethod to   ((r ranged)) 1)
(defclass oneof  (cached)  nil)
(defmethod all   ((o oneof)  ) nil)

;;;; short cuts
(defmacro defnum (what (from to) &body filter)
  (let ((filter1 (or filter `(call-next-method))))
    `(progn (defclass ,what  (ranged)  nil)
      	(defmethod from ((x ,what)) ,from)
      	(defmethod to   ((x ,what)) ,to)    
      	(defmethod ? :around ((it ,what)) ,@filter1))))

(defmacro defone (what (&rest range))
  `(progn   (defclass ,what  (oneof)   nil)
     		(defmethod all  ((x ,what)) ',range)))

;;;; examples
(defnum posreal (0 most-positive-fixnum) (* 1.0 (call-next-method)))
(defnum posint (0 most-positive-fixnum)   (round (call-next-method)))
(defone weekdays (sun mon tues wed thurs fri sat))
(defone bool (t f))

;;;; demo
(defun demo1 ()
  (let ((names '(weekday posint posreal bool)))
    (dolist (name names) (isa name name))
    (dotimes (i 2) 
      (dolist (one names) 
        (format t "~a) ~a = ~a~%" i one (! one))))
    (zap)
    (dotimes (i 2) g
      (dolist (one names) 
        (format t "~a) ~a = ~a~%" i one (! one))))
 ))