anchor.diff:                  :callback)
     (:export :with-signal-handler
              :signal-handler-bind
  -           :*toplevel-signal-handlers*
  +           :signal-handler
   
              :unix-signal
              :signo
  
positive.code: (defvar *toplevel-signal-handlers* nil "Toplevel handler")
  (defvar *signal-handler-hierarchy* nil "Nested cons-tree of signal handlers")
  
  (defun canonical-signal-arg (signal)
    (if (integerp signal)
        signal
        (signal-number signal)))
  
  ;; you no longer able to explicitly access the current handlers.
  
  ;;;; cffi interfaces
  
  
negative.code:   (:report (lambda (c s)
               (format s "~&received ~A~%" (signal-name (signo c))))))
  
  (cffi:defcallback call-signal-handler-in-lisp :void ((signo :int))
    #+debug
    (bt:with-lock-held (*print-lock*)
  