experimenting with a Scala Future/Task like library for Clojure

future.clj

; experiments on a clojure future API
; http/get and/post are expected to return futures

; create a future

(run (Thread/sleep 100)
     123)
; => java.util.concurrent.CompletableFuture[123]

; supports deref, implements java.util.concurrent.Future
(def foo (run "blaa"))

@foo ; => "blaa"

; promote a value, don't launch a future
@(now 123) ; => 123

; then is map
@(then (run 123) (inc))

; => 124

; compose is flatMap
@(compose (run 1234) (fn [x] (run (Thread/sleep 1000) (inc x))))

; => 1235 


; for yield - with interop
(def xyz (promise))
(for [a (run "hello")
      b (future "i am bob")
      c xyz]
  (print (str a b c)))

; time passes

(deliver xyz "blarh")

; prints "helloi am bobblarh"

; sequence a list of tasks into a task list
(sequence (run 1) (future 2) (now 9))

; => [1 2 9]

; traverse with a task producing function
(traverse (fn [x] (run (Thread/sleep (* x 500)))) [1 2 3 4])

; contrived example, real use

; then is map
(def get-location
  (task/then (http/get "http://host.com/stuff")
             cheshire/parse-string))

(defn get-restaurants
  [location]
  (task/then (http/get "http://target.api/restaurants-near-you" {:lat (:latitude location) :lng (:longitude location)})
             cheshire/parse-string))

; compose is flatMap
(defn reserve-restaurant
  [restaurant-id]
  (task/compose (http/post "http://restaurant.reservation/reserve"
                        (cheshire/format-string {:id restaurant-id}))
                (fn [reservation] ; returns a new future!
                  (http/post "http://my.calendar/free"
                             (cheshire/format-string {:time (:start reservation)})))))

(defn best-restaurant
  [restaurants]
  (first restaurants)) ; arbitrary logic here

; for is for yield
(def reserve-nearest-restaurant
  (task/for [location (get-location)
             restaurants (get-restaurants location)
             reservation (reserve-restaurant (:id (best-restaurant restaurants)))]
    (printf "reserved restaurant %s%n" (:name reservation))))

; block until it's reserved
@reserve-nearest-restaurant