Clojure Removing Dependencies on Global State

gistfile1.txt

;; This is a weird LightTable REPL session trying to understand how to actually use the concepts outlined
;; in http://thinkrelevance.com/blog/2013/06/04/clojure-workflow-reloaded and the related talk he gave at
;; Clojure West.
;; The following code does NOT make sense when run in order as I was evaluating things on the fly with LightTable.

(defn system []
  {:db {:conn nil
        :collection "collection"}})
  
(defn start [system]
  (-> system
      (assoc-in [:db :conn] "conn")))

(defn mock []
  {:db {:conn nil
        :collection "mock"}})

(defn stop [system]
  (-> system
      (assoc-in [:db :conn] nil)))

(def sys nil)

(alter-var-root #'system/sys (constantly (start (system))))
(alter-var-root #'system/sys (constantly (start (mock))))

(defn get-shout [db]
  (case (:collection db)
    "collection" "normal shout"
    "mock" "mocked shout"
    "no collection ERROR"))

sys

(defn init-db [db]
  (alter-var-root #'get-shout (constantly (partial get-shout db))))

(init-db (:db (start (system))))

(get-shout)

(init-db (:db (start (mock))))

(let [db (:db sys)]
  (get-shout db))