diff --git a/racket/syndicate/examples/actor/track-set.rkt b/racket/syndicate/examples/actor/track-set.rkt
new file mode 100644
index 0000000..ad0322c
--- /dev/null
+++ b/racket/syndicate/examples/actor/track-set.rkt
@@ -0,0 +1,76 @@
+#lang syndicate/actor
+
+(require racket/set)
+
+(define-syntax-rule (track-set field-name P expr)
+  (let ()
+    (field [field-name (set)])
+    (on (asserted P) (field-name (set-add (field-name) expr)))
+    (on (retracted P) (field-name (set-remove (field-name) expr)))
+    field-name))
+
+(define-syntax-rule (track-hash field-name P key-expr value-expr)
+  (let ()
+    (field [field-name (hash)])
+    (on (asserted P)
+        (let ((key key-expr))
+          (when (hash-has-key? (field-name) key)
+            (log-warning "track-hash: ~a: overwriting existing entry ~v"
+                         'field-name
+                         key))
+          (field-name (hash-set (field-name) key value-expr))))
+    (on (retracted P) (field-name (hash-remove (field-name) key-expr)))
+    field-name))
+
+(define-syntax-rule (track-hash-set field-name P key-expr value-expr)
+  (let ()
+    (field [field-name (hash)])
+    (on (asserted P)
+        (let ((key key-expr))
+          (field-name (hash-set (field-name)
+                                key
+                                (set-add (hash-ref (field-name) key set)
+                                         value-expr)))))
+    (on (retracted P)
+        (let ((key key-expr))
+          (let ((new-entries (set-remove (hash-ref (field-name) key set)
+                                         value-expr)))
+            (field-name (if (set-empty? new-entries)
+                            (hash-remove (field-name) key)
+                            (hash-set (field-name) key new-entries))))))
+    field-name))
+
+(actor #:name 'tracker
+       (forever
+        (define as-set (track-set as-set `(item ,$a ,$b) (list a b)))
+        (define as-hash (track-hash as-hash `(item ,$a ,$b) a b))
+        (define as-hash-set (track-hash-set as-hash-set `(item ,$a ,$b) a b))
+
+        (on (message 'dump)
+            (printf "----------------------------------------\n")
+            (printf "Tracked as-set:\n")
+            (for [(item (as-set))]
+              (match-define (list a b) item)
+              (printf "  ~v -> ~v\n" a b))
+            (newline)
+            (printf "Tracked as-hash:\n")
+            (for [((k v) (in-hash (as-hash)))]
+              (printf "  ~v -> ~v\n" k v))
+            (newline)
+            (printf "Tracked as-hash-set:\n")
+            (for [((k vs) (in-hash (as-hash-set)))]
+              (printf "  ~v -> ~v\n" k vs))
+            (printf "----------------------------------------\n")
+            (flush-output))))
+
+(actor #:name 'mutator
+       (assert! `(item a 1))
+       (assert! `(item b 2))
+       (assert! `(item b 3))
+       (send! 'dump)
+       (retract! `(item b ,?))
+       (send! 'dump)
+       (assert! `(item c 1))
+       (assert! `(item c 4))
+       (send! 'dump)
+       (forever))