Clojure Conditionals — if, when, cond & Truthiness | Episode 5

In most languages, if is a statement. In Clojure, it's an expression that returns a value. This changes everything about how you think about branching. In this episode we explore if, when, and cond — three ways to branch in Clojure. We also uncover a surprise: zero and empty strings are truthy. Only nil and false are falsy. By the end you'll write a conditionals.clj file that demonstrates each pattern plus a cond-based classifier function. Student code: https://github.com/GoCelesteAI/clojure-for-beginners/tree/main/episode05 Every keystroke is shown on screen with generous pauses so you can follow along at your own pace. What You'll Learn: - if as an expression that returns a value (not a statement) - Both branches are required in if — then and else - when for single-branch conditionals (returns nil when false) - Truthiness — only nil and false are falsy; 0, empty string, empty list are all truthy - cond for multi-way branching with condition/result pairs - :else as the default catch-all in cond - Writing a classifier function with cond - Running conditionals.clj with :!clj -M % Key REPL Demo: (if true "yes" "no") returns "yes" (if false "yes" "no") returns "no" (if nil "yes" "no") returns "no" (nil is falsy) (if 0 "yes" "no") returns "yes" (0 is truthy!) (if "" "yes" "no") returns "yes" (empty string truthy!) (when true "hello") returns "hello" (when false "hello") returns nil Timestamps: 0:00 - Intro 0:12 - Preview: branching as expressions 0:32 - Start the REPL (no rlwrap flicker) 0:39 - if basics — true and false 0:53 - Truthiness — nil, 0, empty string 1:12 - when — single branch 1:25 - cond — multi-way branching 1:37 - Exit REPL with Ctrl+D 1:42 - Write conditionals.clj in Neovim 1:54 - if section — bind x, test with if 2:26 - when section 2:50 - Truthiness section — 0, "", nil 3:33 - cond section — describe function 4:39 - Run with :!clj -M % 4:43 - Output explained line by line 5:39 - Review the file 5:49 - Recap 6:17 - What's next — Episode 6 Key Takeaways: 1. if is an expression — it returns a value, not just controls flow. Both branches are required. 2. when handles the single-branch case — returns nil when false. 3. Only nil and false are falsy. Everything else (including 0 and "") is truthy. 4. cond gives you multi-way branching with test/result pairs and :else as the catch-all. 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 6: Your First Script (deps.edn). Taught by CelesteAI. Like & subscribe for more Clojure tutorials!