0Pricing
Clojure Functional Programming & JVM Backend Development · Lesson

REPL-Driven Development Workflow

Learn the power of the Read-Eval-Print Loop (REPL) for interactive and iterative development.

REPL-Driven Development Workflow is a free Clojure Functional Programming & JVM Backend Development lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Clojure Functional Programming & JVM Backend Development learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

What is a REPL?

Welcome to REPL-Driven Development. The Read-Eval-Print Loop lets you run code instantly — like having a live conversation with your program.

The REPL Cycle

The REPL cycle is its name: Read your code, Eval it, Print the result, and Loop for the next input. That tight loop powers fast feedback.

Launching Your REPL

You start a REPL with tools like lein repl or clj, but the idea is constant: an interactive prompt you evaluate code in.

Your First REPL Interaction

Watch a REPL evaluation: type an expression and the result comes straight back. This snippet shows basic math and string ops.

(ns coddykit.core
  (:gen-class))

(defn -main
  "Simulates basic REPL evaluation."
  [& args]
  (println "Result of (+ 10 5):" (+ 10 5))
  (println "Result of (str \"Hello\" \" \" \"REPL!\") :" (str "Hello" " " "REPL!"))
)

Storing Values with `def`

Use def to bind a global value in the REPL. It is immediately available to every expression you evaluate next.

(ns coddykit.core
  (:gen-class))

(defn -main
  "Demonstrates 'def' in a REPL-like context."
  [& args]
  (def my-favorite-number 42)
  (println "My favorite number is:" my-favorite-number)

  (def greeting-message "Welcome to Clojure!")
  (println greeting-message)
)

Creating Functions with `defn`

Define functions interactively with defn. Once defined they are instantly callable — perfect for testing pieces in isolation.

(ns coddykit.core
  (:gen-class))

(defn add-two [num]
  (+ num 2))

(defn -main
  "Demonstrates 'defn' and function calling."
  [& args]
  (println "5 plus 2 is:" (add-two 5))
  (println "10 plus 2 is:" (add-two 10))
)

Building Incrementally

RDD is about building incrementally: write a function, test it, refine it, then compose the next on top. Iteration is the whole point.

Edit, Evaluate, Repeat

Found a bug? Just edit the function and re-evaluate it. The running program updates live — no restart needed.

(ns coddykit.core
  (:gen-class))

(defn calculate-sum [a b]
  (println "Calculating sum...")
  (+ a b))

(defn -main
  "Illustrates REPL's immediate feedback potential."
  [& args]
  (println "First call:" (calculate-sum 7 3))
  ; Imagine you redefined 'calculate-sum' to multiply
  ; and then evaluated it again in the REPL.
  ; The next call would use the new definition!
  (println "Second call:" (calculate-sum 2 8))
)

Why REPL-Driven Development?

RDD wins on fast feedback, free exploration, live debugging of running state, and testing functions in isolation as you go.

REPL Quick Check

The REPL is central to Clojure's interactive development style. Let's ensure you grasp its core function.

REPL Power Up!

Recap: the REPL is an interactive Read-Eval-Print-Loop where you define values and functions on the fly for rapid, iterative development.

Frequently asked questions

Is the “REPL-Driven Development Workflow” lesson free?

Yes — the full text of “REPL-Driven Development Workflow” is free to read here on the web, and the Clojure Functional Programming & JVM Backend Development course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Clojure Functional Programming & JVM Backend Development course, upgrade to CoddyKit PRO.

What will I learn in “REPL-Driven Development Workflow”?

Learn the power of the Read-Eval-Print Loop (REPL) for interactive and iterative development. You practise Clojure Functional Programming & JVM Backend Development with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Clojure Functional Programming & JVM Backend Development?

No prior experience is required. Clojure Functional Programming & JVM Backend Development on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “REPL-Driven Development Workflow” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Clojure Functional Programming & JVM Backend Development lesson?

Yes. Every Clojure Functional Programming & JVM Backend Development lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Introduction to Clojure & JVM
  2. Core Data Structures & Syntax
  3. REPL-Driven Development Workflow
  4. Destructuring and Working with Keywords
← Back to Clojure Functional Programming & JVM Backend Development