Clojure Mount – Clojure docs and tutorials

Once you learn Clojure (or any programming language) well enough to tackle a large project, you are going to run into lifecycle, dependency, and state management issues.

Two great resources for handling lifecycles, dependency, and state in Clojure apps are Mount and Component. I use Mount for my projects, but both are popular solutions. This post is about tolitius/Mount.

Simple Mount Example

The first step in using any Clojure library is to include it as a dependency in your project. I’m using lein, so the project.clj needs the Mount dependency.

:dependencies [
                 [org.clojure/clojure "1.10.1"]
                 [mount "0.1.16"]
                 ]

:dependencies [

[org.clojure/clojure "1.10.1"]

[mount "0.1.16"]

]

You can find the latest dependency code by searching for ‘clojars’ on the Mount project page.

Next, we need some sample code. How about a stateful thread?

(ns example.state-one
  (:require
    [mount.core :refer [defstate]]))

(def should-run (atom true))
(def state-one (atom 0))

(defn- stateful-task-one []
  (doto (Thread.
    (fn []
      (loop []
        (swap! state-one inc)
        (println "internal state is " @state-one)
        (Thread/sleep 1000)
        (if @should-run
          (recur)))))
    (.start))
  state-one)

(defn- stop-it []
  (swap! should-run not)
  (Thread/sleep 2000)
  (println "Stateful task finished."))

(defstate my-stateful-thing
          :start (stateful-task-one)
          :stop (stop-it))

(ns example.state-one

(:require

[mount.core :refer [defstate]]))

(def should-run (atom true))

(def state-one (atom 0))

(defn- stateful-task-one []

(doto (Thread.

(fn []

(loop []

(swap! state-one inc)

(println "internal state is " @state-one)

(Thread/sleep 1000)

(if @should-run

(recur)))))

(.start))

state-one)

(defn- stop-it []

(swap! should-run not)

(Thread/sleep 2000)

(println "Stateful task finished."))

(defstate my-stateful-thing

:start (stateful-task-one)

:stop (stop-it))

Now for a main method to use the stateful dependency.

(ns example.core
  (:require
    [mount.core :as mount]
    [example.state-one :refer [my-stateful-thing]])
  (:gen-class))

(defn -main
  "I don't do a whole lot ... yet."
  [& args]

  (mount/start)

  (println "Checking the current state" @my-stateful-thing)

  (Thread/sleep 3000)

  (println "One more check of the state" @my-stateful-thing)

  (mount/stop)

  (println "All done."))

(ns example.core

(:require

[mount.core :as mount]

[example.state-one :refer [my-stateful-thing]])

(:gen-class))

(defn -main

"I don't do a whole lot ... yet."

[& args]

(mount/start)

(println "Checking the current state" @my-stateful-thing)

(Thread/sleep 3000)

(println "One more check of the state" @my-stateful-thing)

(mount/stop)

(println "All done."))

Running this code should result in output similar to the following

internal state is Checking the current state  1
1
internal state is  2
internal state is  3
One more check of the state 3
Stateful task finished.
All done.

Process finished with exit code 0

internal state is Checking the current state 1

internal state is 2

internal state is 3

One more check of the state 3

Stateful task finished.

All done.

Process finished with exit code 0

This is a very basic example that should be easy to expand upon.

Simple Mount Example

Leave a Reply Cancel reply