interceptors.clj

interceptors.clj

(defn fn-1arity [one-arg]
  (inc one-arg))

(defn fn-future [res]
  (d/future
    (Thread/sleep 1000)
    res))

(defn fn-2arity [a b]
  (+ a b))

(defn side-effect [a]
  (if (> a 10)
    (throw (ex-info (format "Value > 10: %s" a) {:a a}))))

;; we want the following
{:context {:a 1}}
;; call (fn-1arity 1), overwrite :b
{:context {:a 1 :b 2}}
;; call (fn-2arity 1 3), add :c
{:context {:a 1 :b 2} :result 3}
;; call (fn-future [ctx]) to prove it works with deferred returns as easily
{:context {:a 1 :b 2} :result 3}


;;; this is the glue code
@(ixm/execute {:context {:a 1}}
              [;; 1-arity is fine for chaining & lensing
               (-> fn-1arity
                   (ix/in [:context :a])
                   (ix/out [:context :b]))
               ;; 2-arity is clumsy...
               (-> (fn [{{:keys [a b]} :context}] (fn-2arity a b))
                   (ix/out [:result]))
               ;; deferreds work fine and can be chained to the next ix
               (-> fn-future)
               (-> (fn [_] (println "deferred finished!"))
                   (ix/discard))
               ;; side-effects is called "discard"
               ;; try running the ixm chain with {:a 5}
               (-> side-effect
                   (ix/lens [:result])
                   (ix/discard))])