anchor.diff:  
   (optimization-settings)
   
  +(defgeneric syscall-errno (syscall-error)
  +  (:documentation
  +   "Return the errno that was set when the given condition was
  +signaled."))
  +
   (define-condition syscall-error (error)
     ((errno
       :initform errno
  
positive.code:            (let* ((whole (gensym "WHOLE"))
                    (args (apply 'concatenate 'list (mapcar #'macro-argify arg-descriptions))))
               `(defmacro ,lisp-name (&whole ,whole ,@args)
                  (declare (ignore ,@(remove '&rest args)))
                  `(let ((,',result (,',lisp-impl-name ,@(cdr ,whole))))
                     (unless (funcall ,',error-checker ,',result)
  
negative.code:              (format s "Encountered an error (~A) in ~A.  ~A"
                       (syscall-errno c)
                       (syscall-error-function c)
                       (strerror (syscall-errno c)))))
    (:documentation
     "A condition to represent an error in a POSIX C function.
  
  Use `syscall-errno' to access the error code."))
  
  (defun pass (value)
    "Returns t."
  