anchor.diff:    "True when WARNING is a warning about changed function FTYPE."
     #+sbcl
     (when (typep warning '(and warning simple-condition))
  -    (let ((control (simple-condition-format-control warning))
  +    (let ((control (format-control-string-or-nil warning))
             (args (simple-condition-format-arguments warning)))
         (and (search "function" control)
              (search "clobbers" control)
  
positive.code: Returns two values: a boolean and a name symbol of the thing."
    #+sbcl
    (when (typep warning '(and warning simple-condition))     ; not really a simple-warning
      (let ((control (simple-condition-format-control warning))
            (args (simple-condition-format-arguments warning)))
        (cond ((equal control "undefined ~(~A~): ~S")
               (and (eq (first args) kind)
                    (values t (second args))))
              ((equal control "~W more use~:P of undefined ~(~A~) ~S")
  
negative.code:   #-sbcl nil
    #+sbcl
    (when (typep warning '(and warning simple-condition))
      (let ((control (format-control-string-or-nil warning)))
        (search "compiled before a compiler-macro was defined for it" control))))
  
  (deftype compiler-macro-after-function-use ()
  