+
+;;; BUG-OR-ERROR: because we have extensible streams, wherewith the
+;;; user is responsible for some of the protocol implementation, it's
+;;; not necessarily a bug in SBCL itself if we fall through to one of
+;;; these default methods.
+(defmacro bug-or-error (stream fun)
+ `(error "~@<The stream ~S has no suitable method for ~S, ~
+ and so has fallen through to this method. If you think that this is ~
+ a bug, please report it to the applicable authority (bugs in SBCL itself ~
+ should go to the mailing lists referenced from <http://www.sbcl.org/>).~@:>"
+ ,stream ,fun))
+