anchor.diff:    (:documentation
      "Result of a failed output assertion."))
   
  -(defun output-result (test expected actual)
  +(defmethod assert-result ((type (eql :output)) test expected actual)
     "Return the result of an output assertion."
     (declare (ignore test))
     (string=
      (string-trim '(#\newline #\return #\space) (car actual))
      (car expected)))
  -
  -(defun assert-function (type)
  -  "Return the function for the assertion type."
  -  (ecase type
  -    (:equal #'equal-result)
  -    (:error #'error-result)
  -    (:macro #'macro-result)
  -    (:result #'boolean-result)
  -    (:output #'output-result)))
   
   (defun assert-class (type)
     "Return the class for the assertion type."
  
positive.code:   `(lambda ()
       (list ,@(mapcan (lambda (form) (list `',form form)) extras))))
  
  (defclass failure-result ()
    ((form
      :initarg :form
  
negative.code:   (:documentation
     "Result of a failed boolean assertion."))
  
  (defmethod assert-result ((type (eql :result)) test expected actual)
    "Return the result of a result assertion."
    (declare (ignore test))
    (logically-equal (car actual) (car expected)))
  