weak tables with weak value

scheme/weak-table.scm

@@ -0,0 +1,24 @@
+;;; weak table with weak values
+
+(define-record-type weak-table
+  (really-make-weak-table table)
+  weak-table?
+  (table weak-table-table))
+
+(define (make-value-weak-table)
+  (really-make-weak-table (make-integer-table)))
+
+(define (add-to-weak-table! table address object)
+  (table-set! (weak-table-table table)
+	      address 
+	      (make-weak-pointer object)))
+
+(define (remove-from-weak-table! table address)
+  (table-set! (weak-table-table table)
+	      address #f))
+
+(define (lookup-in-weak-table table address)
+  (cond
+   ((table-ref (weak-table-table table) address)
+    => weak-pointer-ref)
+   (else #f)))