a clojure core.async proposal solution to this question: "Clojure (script): macros to reason about async operations synchronously" http://stackoverflow.com/questions/11171066/clojure-script-macros-to-reason-about-async-operations-synchronously

gistfile1.txt

(ns fourclojure.stack
    (require [clojure.core.async :as async :refer :all]))

(defn update-sidebar! [new-data]
  (println "you have updated the sidebar with this data:" new-data))

(defn async-handler [the-channel data-recieved]
  (put! the-channel data-recieved)
  )

(defn make-ajax-call [url data-to-send]
  (let [the-channel (chan)]
    (go   
     (<! (timeout 2000)); wait 2 seconds to response
     (async-handler the-channel (str "return value with this url: " url)))
    the-channel
    )
  )

(update-sidebar! (<!! (make-ajax-call "/fetch-new-data" {})))

and the project configuration:

(defproject fourclojure "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
   :repositories {"sonatype-staging"
                 "https://oss.sonatype.org/content/groups/staging/"}
  :dependencies [
                 [org.clojure/clojure "1.5.1"]
                 [org.clojure/core.async "0.1.0-SNAPSHOT"]
                 ])