goblock.clj

;; Without channels:

;; Makes an HTTP request, and executes the callback on the response when it
;; comes. This should be familiar from Javascript.
(defn get-pudding [callback]
  (http-get {:url "pudding"
             :success callback}))

(get-pudding (fn [response] (eat response)))

;; With channels:

;; Makes an HTTP request, and returns an output channel which will receive the
;; response when it comes.
(defn get-pudding []
  (let [out (chan)]
    (http-get {:url "pudding"
               :success (fn [response]
                          (go (>! out response)))})))

;; This looks like synchronous code, but actually the go block tells it to wait
;; until it's possible to take from the output channel and then eat the result.
(go (eat (<! (get-pudding))))