Clojure

A Lisp hosted on the JVM (and JS via ClojureScript) with a focus on immutability.

When to Use

• Data processing
• Concurrency (Software Transactional Memory)
• Web development
• JVM interop needed

Quick Start

(println "Hello, World!")

(defn square [x]
  (* x x))

(map square [1 2 3]) ; (1 4 9)

Core Concepts

Persistent Data Structures

Immutable lists, vectors, maps, and sets that structurally share data to be efficient.

REPL Driven Development

Writing code interactively in a Running Eval-Print Loop.

Macros

Code that takes code as input and returns code.

Best Practices

Do:

• Use the REPL
• Use threading macros -> and ->> to make code readable
• Leverage JVM libraries

Don’t:

• Use atoms/agents/refs unless you need mutable state
• Write deeply nested parentheses (use structural editing)

References

• Clojure.org
• ClojureDocs