Monads, simple made easier

monads.clj

; A simple demo of monadic composition of side effects
; Program to take 3 nubers as input and print their sum.

(defn read-and-add!
  [prev]
  (print "Enter a number: ")
  (+ prev (do (flush)
              (Integer/parseInt (read-line)))))

(defn bind
  [m next-fn]
  (try
    (next-fn m)
    (catch Exception e (reduced (str e)))))

(defn chain
  [init & effects]
  (reduce bind init effects))

(println (chain 0
                read-and-add!
                read-and-add!
                read-and-add!))