(defn chain-fn [f]
  (fn [[c x]]
    (if (= c ::continue)
      (if-let [result (f x)]
        [::continue result]
        [::short-circuit x])
      [::short-circuit x])))

(defn start-chain [value]
  [::continue value])

(defn stop-chain [[_ value]]
  value)

(defn rev [s]
  (println "calling rev")
  (apply str (reverse s)))

(defn dub [s]
  (println "calling dub")
  (str s s))

(defn break-it [s] nil)

(comment
  "Usage:"
  (-> "Meow"
      start-chain
      ((chain dub))
      ((chain break-it))
      ((chain rev))
      stop-chain)

  )