anchor.diff:    ((event-type :initarg :event-type :reader event-type-of)
      (os-handle :initarg :os-handle :reader os-handle-of))
     (:report (lambda (c s)
  -             (format s "Poll error(event ~S, handle ~A): ~A"
  -                     (event-type-of c) (os-handle-of c) (message-of c))))
  +             (format s "Poll error(event ~S, handle ~A)"
  +                     (event-type-of c) (os-handle-of c))
  +             (when (message-of c)
  +               (format s ": ~A" (message-of c)))))
     (:documentation
      "Signaled when an error occurs while polling for I/O readiness
   of a file descriptor."))
  
positive.code:                :documentation "Keyword identifier, or NIL.")
     (message :initarg :message :reader message-of
              :documentation "Error description."))
    (:default-initargs :code nil :identifier :unknown))
  
  (define-condition system-error (error condition-info-mixin)
    ()
  
negative.code:   ((event-type :initarg :event-type :reader event-type-of)
     (os-handle :initarg :os-handle :reader os-handle-of))
    (:report (lambda (c s)
               (format s "Poll timeout(event ~S, handle ~A)"
                       (event-type-of c) (os-handle-of c))
               (when (message-of c)
                 (format s ": ~A" (message-of c)))))
    (:documentation
     "Signaled when a timeout occurs while polling for I/O readiness
  of a file descriptor."))
  