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Initial Setup

Initial Setup

Get Clojure installed and running your first program. This guide walks you through installation on any operating system and gets you writing code immediately.

🎯 What You’ll Accomplish

By the end of this tutorial, you’ll have:

  • ✅ Clojure and Leiningen installed and verified
  • ✅ Your first Clojure program running
  • ✅ A working REPL for interactive development

📋 Prerequisites

  • Java Development Kit (JDK) 8 or later
  • Basic familiarity with your computer’s terminal/command line
  • No prior Clojure experience required

💾 Step 1: Install Java

Clojure runs on the Java Virtual Machine (JVM), so you need Java installed first.

Verify Java Installation 

java -version

If Java is installed, you’ll see version information. If not, install it:

Install Java

Windows/macOS/Linux: Download from Adoptium (formerly AdoptOpenJDK):

  1. Visit adoptium.net
  2. Download Temurin JDK 17 or later (LTS version recommended)
  3. Run the installer
  4. Verify: java -version

macOS (Homebrew):

brew install openjdk@17

Linux (Ubuntu/Debian):

sudo apt update
sudo apt install openjdk-17-jdk

💾 Step 2: Install Clojure CLI Tools

Windows

Using Scoop:

scoop install clojure

Or download the installer from clojure.org.

macOS

Using Homebrew:

brew install clojure/tools/clojure

Linux 

curl -L -O https://github.com/clojure/brew-install/releases/latest/download/linux-install.sh
chmod +x linux-install.sh
sudo ./linux-install.sh

Verify Installation 

clojure --version

Expected output:

Clojure CLI version 1.11.x.x

💾 Step 3: Install Leiningen (Build Tool)

Leiningen is the most popular Clojure build tool for managing dependencies and projects.

Windows

Download lein.bat and place it in a directory on your PATH.

macOS/Linux 

curl https://raw.githubusercontent.com/technomancy/leiningen/stable/bin/lein > ~/bin/lein
chmod +x ~/bin/lein
lein

The first run will download dependencies.

Verify Installation 

lein version

Expected output:

Leiningen 2.x.x on Java x.x.x

🚀 Step 4: Create Your First Clojure Program

Using REPL (Interactive Shell) 

clojure

You’ll see the Clojure REPL prompt:

user=>

Try some commands:

user=> (println "Hello, Clojure!")
Hello, Clojure!
nil

user=> (+ 1 2 3)
6

user=> (def name "Alice")
#'user/name

user=> (str "Hello, " name "!")
"Hello, Alice!"

user=> (exit)

Type (exit) or press Ctrl+D to exit the REPL.

Create a Project with Leiningen 

lein new app hello-clojure
cd hello-clojure

This creates a new project structure:

hello-clojure/
├── project.clj       # Project configuration
├── src/
│   └── hello_clojure/
│       └── core.clj  # Main source file
└── test/
    └── hello_clojure/
        └── core_test.clj

Edit the Main File

Open src/hello_clojure/core.clj:

(ns hello-clojure.core
  (:gen-class))

(defn -main
  "I don't do a whole lot ... yet."
  [& args]
  (println "Hello, Clojure World!"))

Run Your Program 

lein run

Expected output:

Hello, Clojure World!

✅ Verification Checklist

Before moving forward, verify:

  • java -version shows Java 8 or later
  • clojure --version shows Clojure CLI installed
  • lein version shows Leiningen installed
  • REPL starts with clojure command
  • lein run executes your hello-clojure project

🎉 You’re Done!

You’ve successfully installed Clojure and run your first program. You’re ready for the next step.

📚 What’s Next?

Quick learner: Clojure Quick Start

  • Learn core syntax and basic patterns in one session
  • Understand enough to explore Clojure independently

Code-first learner: Clojure By Example

  • 80 annotated, runnable examples covering 95% of production Clojure

  • Best for experienced developers who prefer learning through code

  • Progressive learning path from beginner to advanced

  • Deep understanding of Clojure’s philosophy and patterns

🆘 Troubleshooting

Java Issues

Problem: “java: command not found”

Solution: Verify Java is installed and in your PATH. Restart terminal after installation.

Clojure CLI Issues

Problem: “clojure: command not found”

Solution: Verify installation completed successfully. On macOS, ensure /usr/local/bin is in your PATH.

Leiningen Issues

Problem: “lein: command not found”

Solution: Verify lein script is in a directory on your PATH. On macOS/Linux, ensure ~/bin is in PATH.

Problem: “Could not find or load main class clojure.main”

Solution: Run lein by itself to download dependencies first.

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