Create a development-only user Namespace.

While doing interactive development, it's important to have a place to put code that is useful for that purpose, but maybe isn't appropriate for the software you ultimately ship.

• Create a file named dev/user.clj

  Most REPLs will automatically load in any user namespace. This makes it the easiest place to put "development only" code.

  (ns user)
             

• Add a :dev alias to your deps.edn.

  You want to have the dev folder included as an extra path.

  {:paths ["src"]
   :deps {...}
   :aliases {...
             :dev {:extra-paths ["dev"]}}}
               

• Add the dev folder to your :nREPL alias as well.

  Seeing as you will only be using nREPL during development, this is needed. We can merge :dev and :nREPL eventually if they become too much to keep in sync.

  {:paths ["src"]
   :deps {...}
   :aliases {:nREPL
              {:extra-paths ["dev"]
               :extra-deps
                {nrepl/nrepl {:mvn/version "1.2.0"}}}
             :dev {:extra-paths ["dev"]}}}
               

• Put a def at the top assigning system to nil.

  (ns user)
  
  (def system nil)

• Put a start-system! function in user.

  This should call start-system from example.system and set the value of the system var to the return value.

  If a system is already started - which you can tell by checking is system is nil - you can print a message and exit early.

  (ns user
    (:require [example.system :as system]))
  
  (def system nil)
  
  (defn start-system!
    []
    (if system
      (println "Already Started")
      (alter-var-root #'system (constantly (system/start-system)))))

• Put a stop-system! function in user.

  If no system has been started this should be a noop.

  (ns user
    (:require [example.system :as system]))
  
  (def system nil)
  
  (defn start-system!
    []
    (if system
      (println "Already Started")
      (alter-var-root #'system (constantly (system/start-system)))))
  
  (defn stop-system!
    []
    (when system
      (system/stop-system system)
      (alter-var-root #'system (constantly nil))))

• Put a restart-system function in user

  When you want a quick way to turn your system off and back on again, it's nice to have such a function available.

  (ns user
    (:require [example.system :as system]))
  
  (def system nil)
  
  (defn start-system!
    []
    (if system
      (println "Already Started")
      (alter-var-root #'system (constantly (system/start-system)))))
  
  (defn stop-system!
    []
    (when system
      (system/stop-system system)
      (alter-var-root #'system (constantly nil))))
  
  (defn restart-system!
    []
    (stop-system!)
    (start-system!))
  
  (defn server
    []
    (::system/server system))

• Put a server function in user.

  The purpose of this will be to let code access the running server.

  (ns user
    (:require [example.system :as system]))
  
  (def system nil)
  
  (defn start-system!
    []
    (if system
      (println "Already Started")
      (alter-var-root #'system (constantly (system/start-system)))))
  
  (defn stop-system!
    []
    (when system
      (system/stop-system system)))
  
  (defn server
    []
    (::system/server system))

• Configure your editor

  Now that we have a :dev alias which includes your development only code, you need to make sure your editor uses that alias when you are developing.

  Again I will defer to the official documentation of those tools. For both Calva and Cursive its simply a button to click in the UI.