Introducing Clojure

By Sachin

October 18, 2013

Clojure has been around for couple of years now. It has been recognized for its features like functional programming, elegance, lisp and JMV support. Unlike many popular dynamic languages, it is fast and written to take advantages of all optimizations possible with modern JVMs.

I personally like clojure because it is lisp. Lisp has very tiny language core with almost no syntax and has a powerful macro support. With this brief introduction lets start setting up Clojure.

lein

Before we start programming in Clojure, lets setup leiningen. Leiningen is for automatic Clojure project setup which will create all necessary file required for any Clojure project.

Download lein binary file from Github and copy it to your ~/bin/ directory.

  wget <https://raw.github.com/technomancy/leiningen/stable/bin/lein>

Add ~/bin PATH in your ~/.bashrc
```
  export PATH=~/bin:$PATH
```
Make the binary executable
```
  chmod a+x ~/bin/lein
```
Finally run the self installer
```
  lein
```

Lein configuration

Lein version-2 uses the idea of profiles. The location of file is ~/.lein/profiles.clj. Create this file if it does not exist.

Sample profiles.clj file

  {:user {:plugins [[lein-difftest "1.3.8"]
                 [lein-marginalia "0.7.1"]
                 [lein-pprint "1.1.1"]
                 [lein-swank "1.4.5"]
                 [lein-exec "0.3.0"]
                 [lein-ring "0.8.7"]]}}

You can see all the required libraries which are default to all Clojure projects.

Upgrade

To upgrade lein to its latest stable version use,
```
  lein upgrade
```

Project/App

Create a project or an app.

Create a project using
```
  lein new my-project
```
Create an app using
```
  lein new app my-stuff
```
Create a noir project(noir is a plugin for web framework)
```
  lein new noir my-web-project
```

REPL

REPL(Read-Eval-Print-Loop) can be your excellent interpreter or debugger while you work on a Clojure project. You can run REPL once you create a project.

Lets say the project name is my-stuff, go to project directory and run REPL using
```
  cd my-stuff
  lein repl
```
Inside repl prompt, run (-main)
```
  my-stuff.core=> (-main)
```

If you have done some change in a code, reload it

  my-stuff.core=> (require 'my-stuff.core :reload)

Run a program using lein (Outside the REPL prompt.)
```
  lein run
```
If you are happy with your app, package it into an executable jar
```
  lein uberjar
```

And run jar file using

  java -jar target/my-stuff-0.1.0-standalone.jar

Library

A Clojure library can be created in a same way.

Create

lein new default my-lib

REPL

lein repl
...

Inside a REPL prompt, simple queries can be performed

user=> (require 'my-lib.core)
nil
user=> (ns my-lib.core)
nil
my-lib.core=> (my-func 3)
9

Dependencies

Add project dependencies to ~/.lein/profiles.clj or your-app/project.clj

Below is my sample profiles.clj file

  {:user {:plugins [[lein-difftest "1.3.8"]
                   [lein-marginalia "0.7.1"]
                   [lein-pprint "1.1.1"]
                   [lein-swank "1.4.5"]
                   [lein-exec "0.3.0"]
                   [lein-ring "0.8.7"]]}}

Or you can have it specific to the project

  (defproject perfect-clojure "0.1.0-SNAPSHOT"
   :description "A simple clojure app to test my environment"
   :url "<http://clojuremadesimple.co.uk>"
   :license {:name "Eclipse Public License"
   :url "<http://google.co.uk>"}
   :dependencies
   :dev-dependencies [[midje "1.4.0"]
                      [autodoc "0.9.0"]]
   :plugins
  )

And setup dependencies using
```
  lein deps
```

Compile

Compile your project in to an executable jar using
```
  lein uberjar
```

Run

Run the standalone jar using

  java -jar target/my-stuff-0.1.0-SNAPSHOT-standalone.jar

Connecting to REPL server

A new REPL server is started at http://localhost:PORT when you invoke
```
  lein repl
```
from a project directory.

You can now connect to existing server using

  lein repl :connect nrepl://localhost:PORT

for example

  lein repl :connect nrepl://127.0.0.1:37451

Generate documentation

Install marginalia
```
  cd ~/.lein
  touch profiles.clj
```
Add following line to profiles.clj (Your marginalia version may be different)
```
  {:user {:plugins }}
```
Then, in your project
```
  cd *path/to/project*
```
Install using
```
  lein deps
```
Generate docs
```
  lein marg
```
Browse docs in a web-browser

file://path/to/my-proj/docs/uberdoc.html

Next (Updated on 03 Feb, 2016)

Checkout this post on Sending an SMS using Clojure.
Clojure from the ground up blog post series by Kyle Kingsbury.

psachin.github.io

Introducing Clojure

lein

Lein configuration

Upgrade

Project/App

Create a project or an app.

REPL

Library

Create

REPL

Dependencies

Compile

Run

Connecting to REPL server

Generate documentation

Next (Updated on 03 Feb, 2016)

References