Clojure Closeable Systems

closeable.clj

(ns closeable-system.core
  (:gen-class)
  (:import (clojure.lang IDeref)
           (java.io Closeable)))

(defn new-database
  [db-spec]
  (println "Starting database component" db-spec)
  {:datasource {}})

(defn new-http-server
  [dependencies config]

  ;; Use config to get host/port
  ;; Has access to dependencies (e.g database)
  (println "Starting http server" config "dependencies" dependencies)
  {:http-server {}})

(defn closeable
  ([value] (closeable value identity))
  ([value close] (reify
                   IDeref
                   (deref [_] value)
                   Closeable
                   (close [_] (close value)))))

(defn my-system
  [config]

  ;; start db
  ;; start server

  (with-open
    [database (closeable
                (new-database (:db-spec config))
                (fn [database]
                  (println "Stopping database" database)))
     http-server (closeable
                   (new-http-server
                     {:database @database}
                     (:http-server config))
                   (fn [http-server]
                     (println "Stopping http server" http-server)))]
    (println "System started" @http-server)
    (Thread/sleep 5000)))

(defn -main
  []
  (println "Hello, World!"))