Getting Clojure

Agents

Returning to our book-inventory example, let’s imagine that we have a new requirement: we need to notify the corporate inventory system of each change in the inventory. Happily, someone else has written a function called notify-inventory-change that takes care of all the notification details. We just need to call it at the right times.

So rolling back to our original, atom-based code, our first stab at this is to just add a call to notify-inventory-change in the inventory-update function:

(def by-title (atom {}))

(defn add-book [{title :title :as book}]
  (swap!
    by-title
    (fn [by-title-map]
      (notify-inventory-change :add book)
      (assoc by-title-map title book))))

;; Similar logic in del-book.

Life is good … until we ...