The threading macro lets us define functions ABOUT data instead of making methods on classes, while still using a top-down ordering of code.

threadingMacro

(defn addCustomer [sale, cust] (assoc sale :customer cust))
(defn addItems [sale, items] (assoc sale :items items))
(defn complete [sale, num] (println "Sale" num ": selling" (:items sale) "to" (:customer sale)))

(def sale { :store "Downtown" })

(-> sale
  (addCustomer "Fred")
  (addItems ["carrot", "eggs"])
  (complete 100)
  )