anchor.diff:                          :name ,name
                           :short-description ,description
                           :description ,description
  +                        :available t
                           :native nil
                           :papi nil)))
   
  
positive.code: 
  (defun format-number (event-name n)
    (when (eql n -1)
      (return-from format-number ""))
    (case event-name
      ((:time :real-time :user-time :system-time)
         (cond ((zerop n) "0")
  
negative.code: 
  (defun report-ascertainableness (results)
    (format t "~2&")
    (let ((widths '(34 13 13 13)))
      (print-table-line widths '("" "non-GC" "GC" "Total")
                        :pad-first-column nil)
      (print-horizontal-separator widths)
      (dolist (result results)
        (destructuring-bind (event total mutator gc) result
          (print-table-line
           widths
           (cons (concatenate 'string
                              (event-description-or-name event (1- (car widths))) ":")
                 (mapcar (lambda (x) (format-number (event-name event) x))
                         (list mutator gc total)))
           :align-first-column :right
           :pad-first-column nil))))
    (terpri))
  
  (defmacro ascertain (form &key (events '(default-events)))
    `(call-with-measurements
      ,events (lambda () ,form) #'report-ascertainableness))
  