Let weak-table-ref kill the entry if the value is #f.

scsh/weaktables.scm

@@ -9,7 +9,13 @@
 
 (define (weak-table-ref table number)
   (let ((ref (table-ref table number)))
-    (if (weak-pointer? ref) (weak-pointer-ref ref) ref)))
+    (if (weak-pointer? ref)
+	(let ((val (weak-pointer-ref ref)))
+	  (if val
+	      val
+	      (begin (table-set! table number #f)
+		     #f)))
+	  ref)))
 
 (define (weak-table-walk proc table)
   (table-walk