Network closures in Clojure, from Chapter 6 of "On Lisp."

on-lisp-chapter-6.clj

;; Figure 6.2 – Representation and definition of nodes
(def nodes (atom {}))

(defn defnode [name contents & [yes no]]
  (swap! nodes assoc name {:contents contents :yes yes :no no}))

;; Figure 6.3 – Sample network
(defn make-nodes [node-maker]
  (node-maker :people "Is the person a man?" :male :female)
  (node-maker :male "Is he living?" :live :dead)
  (node-maker :dead "Was he from the USA?" :USA :elsewhere)
  (node-maker :USA "Is he on a coin?" :coin :no-coin)
  (node-maker :coin "Is the coin a penny?" :penny :other-coin)
  (node-maker :penny "Abraham Lincoln."))

;; Figure 6.4 – Function for traversing networks
(defn run-node [name]
  (let [node     (@nodes name)
        contents (node :contents)
        yes      (node :yes)
        no       (node :no)]
    (if yes
      (do
        (println contents)
         (if (= "yes" (read-line))
           (run-node yes)
           (run-node no)))
      (println contents))))

;; Figure 6.5 - A network compiled into closures
(defn def-closure-node [name contents & [yes no]]
  (swap! nodes assoc name
         (if yes
           (fn []
             (println contents)
             (if (= "yes" (read-line))
               ((@nodes yes))
               ((@nodes no))))
           (fn []
             (println contents)))))

ecmendenhall, how is going?
Have you read any of peter norvig's book?