etude/client/events/session/update.esl

(lambda (new-state)
  (= new-state (JSON.parse new-state))

  (.map (Object.keys new-state) (lambda (device-type-name)
    (var device-type (introduce device-type-name))
    (var new-devices (get new-state device-type-name))
    (.map (Object.keys new-devices) (lambda (device-id)
      (device-type.put device-id (get new-devices device-id))))))

  (function introduce (device-type)
    (if (! (get /state/session device-type))
      (/state/session/put device-type (object)))
    (return (/state/session/get device-type))))