Project templates can be as excellent as they can be awful since they are very opinionated beings:

But they can be really useful for quick prototypes, for learning new things, even for “real deal”, if of course you agree with their opinion.

I’ve recently built a template WWW to bootstrap web apps based on Clojure, ClojureScript, Compojure and Ring. Reason? I needed a faster way of getting apps up and running, especially when prototyping ideas.

Building a Leiningen template is quite a simple task. Once the template is build and installed/deployed, I could just do lein new www whatsapp and make my next $19 billion. But I wanted more!

WWW by default would create a project template with a very simple structure that can be immediately brought up (e.g. “lein ring server”) removing any obstacles on the way of making billions, everything is setup: just open vi and start hacking.

However, what if I want a ClojureScript REPL connected to my browser? I would need to go through some docs, and then depending on my experience with lein, Clojure and ClojureScript, I could quickly (or not) set it up myself.

Well, I wanted WWW template to have that setup for me right away. But here is a dilemma: sometimes I do want ClojureScript browser connected REPL, other times I don’t, and the way this REPL setup goes, it requires a code change to enable/disable it.

The documented way of creating a lein template does not really talk about “options” that I want with my REPL. What do I do? Well.. It’s a Clojure universe, and, if anything, two things hold true most of the time:

A brand new lein template is done with lein new template www. It creates.. ready? “a template for a template”. That’s right, a template project to create a lein template.

An entry point into this template (of a template) will be located in src/leiningen/new/www.clj. Here www is the name of this template. Let’s peek inside:

$ lein new template www
Generating fresh 'lein new' template project.
$ cd www
$ cat src/leiningen/new/www.clj

(ns leiningen.new.www
  (:use [leiningen.new.templates :only [renderer name-to-path ->files]]))
 
(def render (renderer "www"))
 
(defn www
  "FIXME: write documentation"
  [name]
  (let [data {:name name
              :sanitized (name-to-path name)}]
    (->files data
             ["src/{{sanitized}}/foo.clj" (render "foo.clj" data)])))

See? www here is just a function, that in this case, takes a name parameter. And after this template is installed lein new www whatsapp will pass whatsapp to it.

Since www is just a function, why not make it take optional parameters which could potentially change the resulting template?

(defn www
  "Create a new Clojure + ClojureScript + Compojure + Ring project"
  ([name] 
   (www name :noop))
  ([name opts]
  ...))

Great! Now www can either take just name as before, or name and some magic opts. How about one of the options will determine whether or not a template with ClojureScript browser connected REPL is added? I think yes.

And now we can do:

which will create two different flavors of the same template.

This entry was posted on Saturday, March 8th, 2014 at 00:46 and is filed under clojure, clojurescript, lein. You can follow any comments to this entry through the RSS 2.0 feed. You can leave a comment, or trackback from your own site.