Promise.all with core.async

promise.cljs

(ns cljs-made-easy.core
  (:refer-clojure :exclude [into])
  (:require-macros [cljs.core.async.macros :refer [go go-loop]])
  (:require [cljs.core.async :refer [<! >!] :as a]))

(enable-console-print!)

(defn resolving-promise [key t reject]
  (go
    (pr (str key " starting"))
    (<! (a/timeout t))
    (pr (str key " finished"))
    (str key " waited " t "ms")))

(defn rejecting-promise [key t reject]
  (go
    (pr (str key " starting"))
    (<! (a/timeout t))
    (>! reject (str key " had an error after " t "ms"))
    "This string won't be used"))

(defn into [coll & chans]
  (go-loop [coll coll
            chans chans]
    (if (seq chans)
      (recur (conj coll (<! (first chans)))
             (rest chans))
      coll)))

(defn all [reject & chans]
  (go
    (let [all-chans (apply into [] chans)
          [v ch] (a/alts! [reject all-chans])]
      (if (= ch reject)
        (pr (str "Rejected value: " v))
        (pr (str "Resolved values: " v))))))

(defn demo-resolving []
  (let [reject (a/chan)]
    (go
      (<! (all reject
               (resolving-promise :c1 2000 reject)
               (resolving-promise :c2 1000 reject)
               (resolving-promise :c3 1500 reject))))
    nil))

(defn demo-rejecting []
  (let [reject (a/chan)]
    (go
      (<! (all reject
               (resolving-promise :c1 2000 reject)
               (resolving-promise :c2 1000 reject)
               (rejecting-promise :c3 1500 reject))))
    nil))