My foray into functional programming began recently with Clojure. Emacs is the recommended IDE for Clojure as Emacs was built using Lisp and is relatively easy to setup. I’m not a fan of having to use keybinds to do perform basic function, which Emacs requires, and I love my regular IDE Atom too much.

Setting up Atom to program with Clojure effectively was quite the struggle, requiring configs from several sources. This was partly due to the previously most popular Clojure REPL environment for Atom ‘Proto-REPL’ no longer being maintained.

I’ll go through the steps required to program Clojure in Atom effectively below, fully tested and working at time of writing.

### Requirements

You’ll need to install these first:

1. Java Development Kit
2. Atom
3. Leiningen

Instructions to install the above can be found here. You can use Clojure CLI instead of Leiningen but this tutorial will focus on Leiningen.

### Atom packages

A major part of Clojure is the REPL, Read Eval Print Loop. Chlorine is the up-to-date package that provides this inside Atom.

To install Chlorine, and other Atom packages recommended for using Atom as a Clojure IDE, run this in an elevated command prompt:

apm install chlorine lisp-paredit parinfer platformio-ide-terminal

Using Chlorine is most efficient with specific keymaps. I use the ones by Sean Corfield here. Download the repo as a zip (Code > Download zip) and extract it directly into your Atom folder (on Windows this is located at C:\Users\$USER.atom). Then, open keymap.cson and change

'atom-workspace atom-text-editor:not([mini])': to 'atom-text-editor[data-grammar="source clojure"]':.

This last part I will largely copy from the Chlorine quickstart guide as they explain it effectively and concisely:

#### Connecting and running REPL

Chlorine needs to connect to a running REPL to evaluate code. The shortest and easiest way to do this is the following:

1. Open up the terminal by pressing the + in the bottom left of Atom

2. Change to a directory with a Clojure project or create one with and move to its directory:

lein new app <APP_NAME>
cd <APP_NAME>


You do not exactly need to have a previous clj project or even a .clj file, but this step makes your life easier by handling the app’s files

1. Inside the app directory, start a REPL environment with an specific port to connect to it later. Note that for my environment only the second simpler command works for me to start REPL.
# Recomended, pure Socket REPL
JVM_OPTS='-Dclojure.server.myrepl={:port,5555,:accept,clojure.core.server/repl}' lein repl
# OR you can use nREPL
lein repl :start :port 5555

1. In Atom, open the app folder or a single .clj file (or create one if you didn’t do this before).

2. Connect Chlorine to the running REPL, typing ctrl+shift+p and then, Repl, to open Connect Socket Repl. In the next window set host to localhost and port to 5555 (or any other port that you have specified).

3. Refer to the specific keybindings inside keymap.cson to use the REPL to evaluate blocks and selections of code.

This tutorial doesn’t cover usage of Chlorine but Between Two Parens has a guide here that helped me quite a bit.

Questions? Comments? Please feel free to let me know either below or via my contact page.