Toy file server example

minimart/actor.rkt

@@ -436,7 +436,7 @@
 				       #`(#:when #,condition)
 				       #'())
 				(#,(if pub? #'pub #'sub) #,gestalt-stx
-				 #:meta-level #,meta-level)))))
+				 #:meta-level #,(or meta-level 0))))))
 
    (define (push-action! action-stx)
      (define-temporaries [temp action-stx])

minimart/examples/toy-file-server.rkt

@@ -0,0 +1,35 @@
+#lang minimart
+
+(struct save (filename body) #:prefab)
+(struct contents (filename body) #:prefab)
+
+(actor #:name file-server
+       #:state [files (hash)]
+
+       (subscribe (save ($ filename) ($ body))
+         #:update [files (hash-set files filename body)]
+         #:update-routes)
+
+       (observe-subscribers (contents ($ filename) ?)
+         #:level 1
+         #:name observed-filenames
+         #:set filename)
+
+       (for/advertise [(filename observed-filenames)
+                       #:when (hash-has-key? files filename)]
+         (contents filename (hash-ref files filename))))
+
+(define (spawn-file-watcher filename)
+  (actor #:name observer-of-files
+         (observe-advertisers (contents filename ($ file-contents))
+           #:name file-contents
+           #:set file-contents
+           (printf "Contents of ~a: ~v\n" filename file-contents))))
+
+(spawn-file-watcher 'a)
+(spawn-file-watcher 'b)
+(spawn-file-watcher 'c)
+(send (save 'a "first file"))
+(send (save 'b "second file"))
+(send (save 'c "third file"))
+(send (save 'b "second file, second version"))