Starting an nREPL server for a Clojure application is trivial if you use Leiningen:

lein repl # or: lein repl :headless

But what if you have an application deployed as a JAR (or WAR in an application server) and you want to have remote access to an nREPL server? Fortunately, it's easy to start one programmatically:

(require '[clojure.tools.nrepl.server :refer (start-server stop-server)]) ; Starting an nREPL server is trivial: (defonce nrepl-server (start-server :port 12345)) ; So is stopping it: (stop-server nrepl-server)

It works out of the box if you use Emacs with Cider to connect to it, but if you use Light Table, you need to add an additional nREPL middleware to support some functionality that LT needs to work properly. Again, this is easy if you use Leiningen: you just need to declare the dependency to the middleware and add some :repl-options :

(defproject some-awesome-thing "0.1.0-SNAPSHOT" :description "FIXME: write description" :dependencies [[org.clojure/clojure "1.5.1"] [lein-light-nrepl "0.0.13"]] :repl-options {:nrepl-middleware [lighttable.nrepl.handler/lighttable-ops]})

Using the lighttable-ops nREPL middleware programmatically is also quite easy, but you have to know how to compose nREPL middlewares. First, you need to add the dependency to the LT middleware in your project.clj as before:

(defproject some-awesome-thing "0.1.0-SNAPSHOT" :description "FIXME: write description" :dependencies [[org.clojure/clojure "1.5.1"] [lein-light-nrepl "0.0.13"]])

Then you can add it to the middlewares chain in your code:

(require '[clojure.tools.nrepl.server :refer (start-server stop-server)]) (require '[lighttable.nrepl.handler :refer [lighttable-ops]]) ; Starting a server with custom middlewares is trivial: (defonce nrepl-server (start-server :port 12345 :handler (default-handler #'lighttable-ops))) ; So is stopping it: (stop-server nrepl-server)

Notice that we passed lighttable-ops to the default-handler as a var (in fact, #'lighttable-ops is a reader macro that expands to (var lighttable-ops) ).

Now you can connect to your project remotely using Light Table and inspect, modify and control it live. Enjoy :)