+
+;;; This is used in constructing arg lists for debugger printing,
+;;; and when needing to print unbound slots in PCL.
+(defstruct (unprintable-object
+ (:constructor make-unprintable-object (string))
+ (:print-object (lambda (x s)
+ (print-unreadable-object (x s)
+ (write-string (unprintable-object-string x) s))))
+ (:copier nil))
+ string)