0.9.16.25: build fix for CMUCL and older SBCLs

[sbcl.git] / src / pcl / slots.lisp

diff --git a/src/pcl/slots.lisp b/src/pcl/slots.lisp
index a37f983..1b1326b 100644 (file)
--- a/src/pcl/slots.lisp
+++ b/src/pcl/slots.lisp
@@ -136,9 +136,12 @@
   (let ((class (class-of object)))
     (not (null (find-slot-definition class slot-name)))))
 
+(defvar *unbound-slot-value-marker* (make-unprintable-object "unbound slot"))
+
 ;;; This isn't documented, but is used within PCL in a number of print
 ;;; object methods. (See NAMED-OBJECT-PRINT-FUNCTION.)
-(defun slot-value-or-default (object slot-name &optional (default "unbound"))
+(defun slot-value-or-default (object slot-name &optional
+                              (default *unbound-slot-value-marker*))
   (if (slot-boundp object slot-name)
       (slot-value object slot-name)
       default))