Retriable functions, written in CPS

gistfile1.clj

(ns planck-server-nio.common
  (:require (clojure.algo [monads :as m])))

(defn fail   [x] (fn [c] nil))

(defn attempt [[a t f]]
  (fn [c]
    (if-let [result (f)]
      result
      (c [(inc a) t f]))))

(defn delay [[a t f]]
  (fn [c]
    (Thread/sleep (t a))
    (c [a t f])))

(m/with-monad m/cont-m
  (defn retry [n t f]
    (let [backoff (if (number? t) (constantly t) t)
          steps (concat (take (* n 2) (cycle [attempt delay])) [fail])
          cont  ((m/m-chain steps) [0 backoff f])]
      (run-cont cont))))