Clojure Functions with defn — The One Form You Need | Episode 4

Functions are Clojure's main building block. In this episode we cover defn — the one form you use to define every named function in your codebase. By the end you'll know parameters, return values, docstrings, and multi-arity, and you will have written a functions.clj file that ties them all together. No classes, no method vs. function distinction, no void return types. Just defn. Student code: https://github.com/GoCelesteAI/clojure-for-beginners/tree/main/episode04 Every keystroke is shown on screen with generous pauses so you can follow along at your own pace. What You'll Learn: - defn — the canonical way to define a named function - Parameters in a vector after the function name - Return values — the last expression in the body is what comes back, no return keyword - Docstrings — an optional string between name and parameter vector - Multi-arity — one function with different bodies for different argument counts - Writing and running functions.clj with :!clj -M % Key REPL Demo: (defn greet [name] (str "Hello, " name)) defines greet (greet "Ada") returns "Hello, Ada" (defn add [a b] (+ a b)) two arguments (add 3 5) returns 8 (defn square [x] (* x x)) last expression returns (square 7) returns 49 Timestamps: 0:00 - Intro 0:12 - Preview: the one form for functions 0:27 - Start the REPL 0:31 - A simple function: greet 0:45 - Multiple arguments: add 0:57 - Return value is the last expression: square 1:11 - Exit the REPL with Ctrl+D 1:16 - Write functions.clj in Neovim 1:38 - Simple function section 2:12 - Math section — add and square 3:05 - Docstring section — cube 3:40 - Multi-arity section — hello 4:40 - Run with :!clj -M % 4:44 - Output explained line by line 5:40 - Review the file 5:44 - Recap 6:10 - What's next — Episode 5 Key Takeaways: 1. defn defines a named function in one form. Parameters go in a vector after the name. 2. The last expression in the body is always the return value. No return keyword in Clojure. 3. One function can have multiple arities — wrap each arity in its own (params body) parens. Series Roadmap: - Episodes 1-6: REPL & first values - Episodes 7-13: Collections & sequences - Episodes 14-19: Functional core - Episodes 20-24: Namespaces, projects, testing - Episodes 25-30: State & concurrency - Episodes 31-35: Data modeling - Episodes 36-38: Macros - Episodes 39-41: Interop, Babashka, uberjars - Episodes 42-45: Capstone — web app deployment Next up — Episode 5: Conditionals (if, when, cond). Taught by CelesteAI. Like & subscribe for more Clojure tutorials!