(defklass bounded ()
  all
  (bound 20)     ; make size of 'all'
  (n 0)          ; current size of 'all'
  (max *least*)  ; key of top item of 'all'
  ready          ; false if "all" needs a sort
  (key #'identity)
  (value #'identity)
)  

(defmethod print-object ((b bounded) str)
  (in bounded b
      (format str "bound= ~a~%max= ~a~%ready= ~a~%n=~a~%all=~a"
	      bound max ready n all)))

(defun boundeds (b)
  (in bounded b
      (unless ready
	  (setf all   (sort all #'> :key key)
		ready t))
      all))

(defun boundedp (b)
  (boundeds b)
  (in bounded b
      (and
       (<= n bound)
       (= max (funcall key (first all))))))

(defun bounded-pair+ (key value b)
  (bounded+ (cons key value) b))

(defun bounded+ (new b) 
  (in bounded b
      (if (<  n bound)
	  (setf n     (1+ n)
		all   (cons new all)
		max   (max  (funcall key new) max)
		ready nil)
	  (when (< (funcall key new) max)
	    (pop all)
	    (setf all   (sort (cons new all) #'> :key key)
		  max   (funcall key (first all))
		  ready t))))
  b)	 

(defun bounded-pairs ()
  (make-instance 'bounded 
		 :key  #'car 
		 :value #'cdr))

(deftest  ?bounded-nums ()
  (let ((b (make-instance 'bounded)))
    (reset-seed)
    (dotimes (i 1000)
      (bounded+ (randi 100) b))    
    (test     (format nil "b:~a~%boundedp=~a" b (boundedp b)) "
        b:bound= 20
        max= 2
        ready= T
        n=20
        all=(2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 0 0 0 0)
        boundedp=T"
    )))

(deftest  ?bounded-pairs ()
  (let ((b (bounded-pairs)))
    (reset-seed)
    (dotimes (i 1000)
      (bounded+ (cons (randi 100) 'a) b))
    (format nil "b:~a~%boundedp=~a" b (boundedp b))))