For a spartan yet still productive set-up to rapidly get you going, I recommend for now just using a text editor and a terminal window or two. Details below.
If you’d like to use Eclipse or Vim, see their respective tutorials at CDS.
For an easy-to-use GUI editor, try jEdit as described in the Dev Tools guide at CDS.
Whenever you want to start writing a Clojure application or library, it’s most common to first create a new project for it.
Aside: You can also create a self-contained Clojure program in its own single source code file, like a shell script. That is covered later, in the Standalone Scripts chapter. For now though, we’ll discuss the customary way of creating a Clojure program, which is to create a project for it.
A project is just a directory (named after the project) which should contain:
- a project.clj file,
- a README.md file,
- your source code, and
- usually other sundry files.
The tool that’s used to create and manage Clojure projects is called Leiningen (“line-ing-en”), or just “lein” for short (which is also the name of the Leiningen command-line program). We’ll discuss lein in greater detail in a later chapter.
To start tinkering around with some Clojure code, we first need to install Leiningen and then use it to create a little project within which to work.
Create a ~/bin dir if you don’t already have one (and make sure it’s on your $PATH), and install lein like so:
cd ~/bin wget https://raw.github.com/technomancy/leiningen/stable/bin/lein chmod +x lein lein self-install
(Lein’s self-install will create ~/.lein and ~/.m2 directories.)
Create a new application program / script project:
$ cd ~/temp $ lein new app my-app Generating a project called my-app based on the 'app' template. $ cd my-app
Open project.clj in your editor and change the version string from “0.1.0-SNAPSHOT” to just “0.1.0”.
Open up src/my_app/core.clj as well.
Note: in your source code you use the hyphen (ex. “my-app”), but — due to the underlying Java platform — corresponding directory names below the project directory must instead use an underscore (ex. “my_app”).
-main function is just what it looks like (your program’s main entry point). Back in your terminal, from your project directory, start up a repl and call
$ lein repl ... my-app.core=> (-main) Hello, World! nil
Over in your editor, change that “Hello, World!” text to something else and save the file. Now back in the repl, reload the file and run
my-app.core=> (require 'my-app.core :reload) nil my-app.core=> (-main) Hello, You! nil
Quit the repl using Ctrl-d. Now run your program like so:
$ lein run
When you’re happy with your app, package it up and copy the resulting jar file to your ~/bin directory:
$ lein uberjar $ cp target/my-app-0.1.0-standalone.jar ~/bin
and run it:
$ java -jar ~/bin/my-app-0.1.0-standalone.jar Hello, You!
You can now send that jar file to a friend and they should be able to run it likewise (as long as they have Java installed).
:) To make it even easier to run your Clojure app, see distributing apps.
To create a Clojure library:
cd ~/temp lein new default my-lib # Or `lein new my-lib` for short. cd my-lib
In your editor, open src/my_lib/core.clj and between the
(ns ...) and the
(defn foo ...), add your own function:
(defn my-func "Docstring for my-func." [x] (* x x))
Save the file. Back in the terminal, start up a repl and try out that new function:
$ lein repl ... user=> (require 'my-lib.core) nil user=> (ns my-lib.core) nil my-lib.core=> (my-func 3) 9 my-lib.core=> (doc my-func) ------------------------- my-lib.core/my-func ([x]) Docstring for my-func. nil
my-func, change the “*” to a “+”, then try out your changes:
my-lib.core=> (require 'my-lib.core :reload) nil my-lib.core=> (my-func 3) 6
Incidentally, anytime you want to fire up a repl — say, for reading docstrings or for just trying things out — you can do so outside of and without need of a project. For example:
$ cd ~/temp $ lein repl ... user=>
While you’re learning and experimenting with Clojure, your workflow will likely be something like this:
- open your project’s src/my_proj/core.clj in your editor
cdinto your project directory and start up the repl (
- switch to one of the namespaces you’ve made (ex.
- interactively call various functions
- edit your code, then reload it:
(require 'my-proj.core :reload)
- go to step 4