GitHub - AquiGorka/clojure-lessons: From zero to hero

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Learn Clojure: From Zero to Hero

Welcome to your comprehensive Clojure learning journey! This collection of 23 sequential lessons will take you from absolute beginner to advanced Clojure developer.

🚀 Getting Started

Prerequisites

  1. Java JDK 8+ - Clojure runs on the JVM
  2. Clojure CLI - Install from clojure.org 
    # macOS
brew install clojure/tools/clojure

# Linux
curl -O https://download.clojure.org/install/linux-install-1.11.1.1435.sh
chmod +x linux-install-1.11.1.1435.sh
sudo ./linux-install-1.11.1.1435.sh

Starting the REPL

Recommended Editors

  • VS Code + Calva (beginner-friendly)
  • Emacs + CIDER (powerful)
  • IntelliJ + Cursive (great for Java developers)
  • Vim + Conjure (lightweight)

📚 Learning Path

Part 1: Foundations (Lessons 1-5)

Lesson File Topics
01 01_introduction_and_setup.clj What is Clojure, installation, REPL basics
02 02_basic_data_types.clj Numbers, strings, keywords, symbols, booleans
03 03_collections.clj Lists, vectors, maps, sets
04 04_functions.clj defn, anonymous functions, arity, destructuring
05 05_control_flow.clj if, when, cond, case, boolean operators

Part 2: Core Concepts (Lessons 6-10)

Lesson File Topics
06 06_sequences_and_laziness.clj Sequences, lazy evaluation, infinite sequences
07 07_higher_order_functions.clj map, filter, reduce, comp, partial
08 08_destructuring.clj Sequential & map destructuring, nested patterns
09 09_let_bindings_and_scope.clj let, letfn, if-let, when-let, dynamic scope
10 10_threading_macros.clj ->, ->>, as->, some->, cond->

Part 3: Real-World Clojure (Lessons 11-15)

Lesson File Topics
11 11_namespaces_and_organization.clj ns, require, import, project structure
12 12_error_handling.clj try/catch, ex-info, ex-data, assertions
13 13_atoms_and_state.clj Atoms, swap!, reset!, validators, watches
14 14_protocols_and_records.clj defprotocol, defrecord, extend-type, reify
15 15_multimethods.clj defmulti, defmethod, hierarchies

Part 4: Advanced Topics (Lessons 16-23)

Lesson File Topics
16 16_macros.clj defmacro, syntax quote, macroexpand
17 17_refs_and_agents.clj STM, dosync, Refs, Agents, concurrency
18 18_java_interop.clj Calling Java, creating objects, interop patterns
19 19_transducers.clj Composable transformations, performance
20 20_spec.clj Data validation, generative testing
21 21_core_async.clj Channels, go blocks, CSP-style concurrency
22 22_testing.clj clojure.test, fixtures, mocking, property-based testing
23 23_real_world_applications.clj Project structure, web apps, databases, deployment

🎯 How to Use These Lessons

  1. Read the lesson file - Each file is heavily commented with explanations
  2. Try the code in REPL - Copy/paste examples and experiment
  3. Do the exercises - Found at the end of each lesson
  4. Move to the next lesson - They build on each other

Loading a Lesson in REPL

;; Start REPL in this directory
clj

;; Load a lesson file
(load-file "01_introduction_and_setup.clj")

🗺️ Quick Reference

Essential Functions

;; Collections
(first coll)    (rest coll)     (cons x coll)
(conj coll x)   (into to from)  (count coll)
(get coll key)  (assoc m k v)   (update m k f)

;; Sequences
(map f coll)    (filter pred coll)    (reduce f init coll)
(take n coll)   (drop n coll)         (range)

;; Functions
(defn name [args] body)
(fn [args] body)
#(+ % 1)

;; Flow Control
(if test then else)
(when test & body)
(cond & clauses)

Truthiness

  • Falsy: false and nil
  • Truthy: Everything else (including 0, "", [])

Threading Macros

(-> x (f a) (g b))   ; Thread first: (g (f x a) b)
(->> x (f a) (g b))  ; Thread last:  (g b (f a x))

🧩 Practice Problems

Once you've completed the foundational lessons, test your skills with our collection of LeetCode-style problems in the problems/ folder!

What's Included

  • 15 Easy Problems - Two Sum, Valid Parentheses, Climbing Stairs, and more
  • 15 Medium Problems - Group Anagrams, 3Sum, Coin Change, Word Search, etc.
  • 10 Hard Problems - Median of Sorted Arrays, N-Queens, Edit Distance, etc.

Why Practice in Clojure?

  • Learn to approach algorithmic problems with functional thinking
  • Discover how Clojure's rich standard library leads to elegant solutions
  • Prepare for coding interviews while deepening your Clojure knowledge

Getting Started

;; Load a problem file
(load-file "problems/easy_01_two_sum.clj")

;; Run the tests
(run-tests)

See problems/README.md for the full problem index and solving tips.

📖 Additional Resources

Official

Books

  • "Clojure for the Brave and True" by Daniel Higginbotham (free online)
  • "Programming Clojure" by Alex Miller
  • "The Joy of Clojure" by Michael Fogus

Practice

Community

💡 Tips for Success

  1. Embrace the REPL - It's your playground and debugging tool
  2. Think in transformations - Data in, data out
  3. Start simple - Clojure rewards small, composable functions
  4. Read error messages - They're usually helpful
  5. Use the docs - (doc fn-name) in REPL
  6. Practice daily - Even 15 minutes helps

Happy learning! 🎉

"Clojure is the result of many years of thinking about programming, and realizing that most of what I was doing wasn't programming, but rather working around programming language shortcomings." — Rich Hickey