gistfile1.clj

(use 'clojure.contrib.monads)

(defn new-pair [value log] {:value value :log log})
(defn starting-pair [value] (new-pair value nil))

(defn log [base-value]
  (fn [log]
    (new-pair base-value (cons base-value log))))

(defmonad logging-m
  "A monad that logs"
  [m-result (fn [base-value]
              (fn [log] (new-pair base-value log)))
   m-bind (fn [step-fn rest-fn]
            (fn [log]
              (let [{step-value :value, updated-log :log} (step-fn log)]
                ( (rest-fn step-value) updated-log))))])

(def steppy (domonad logging-m
               [a (m-result 5)
                b (log (inc a))
                c (log (+ b a))]
               (* c b a)))

(steppy [])

clojure logger monad by "Briay Marick" demonstrated in vimeo video http://vimeo.com/21307543