Workflow for restarting a HTTP server from Clojure REPL

A Clojure-based project of mine uses the netty (required by aleph) web server. I start the server, along with other components, in a web.clj file like this:

(ns myproject.web)

(def server (atom nil))

(defn initialize []
  (if @server
    (println "Warning: already initialized")
    (let [port 8001]
      (println (format "Starting http://localhost:%s/" port))
      (swap! server (fn [_] (start-http-server
                             (wrap-ring-handler app-routes)
                             {:port port}))))))

(defn shutdown []
  (when @server
    (do
      (println "Shutting down web server")
      (@server)
      (swap! server (fn [_] nil)))))

(defn reinitialize []
  "Run this on the REPL to reload web.clj and restart the web server"
  (myproject.web/shutdown)
  (use :reload-all 'myproject.web)
  (myproject.web/initialize))

The server instance is stored in a Clojure atom, so that it can be stopped later.

I use Emacs and Swank to directly launch the server on the REPL like this (after compiling web.clj with C-c C-k):

user> (myproject.web/initialize)

Whenever web.clj or other dependent modules are edited, I must

1. remember NOT to recompile web.clj using C-c C-k because the atom holding the running instance would vanish (due to the atom from a newly compiled module) from the REPL.

2. Run (myproject.web/reinitialize) which stops the server and then reloads the module before starting it again.

There are two problems with this:

• Often I forget point #1 and press C-c C-k anyway. This causes the loss of server atom in REPL, leading to having to kill swank (or restart emacs) so that I can start the server at the same port number.

• 开发者_StackOverflow中文版:reload-all doesn't report compile errors as friendly as C-c C-k (ugly traceback vs concise clickable errors).

How can I best address these two problems in this edit-compile-restart workflow?

You can replace

(def server (atom nil))

with

(defonce server (atom nil))

that way when you evaluate the buffer it will not redefine server.

for your first problem you can store the atom in a different namespace and on load only overwrite it if it is not yet defined. putting it in it's own namepspace will prevent it from being erased by the reload-all