The other functional programming — Clojure workshop

A 90-minute talk for developers coming from Java, F#, and TypeScript. Two big ideas: values and code as data. One deck, three demo files.

Prerequisites

• Clojure CLI (any recent version)
• Node.js — for the slides (Slidev) and the 30-second JavaScript hook

Running things

Slides — a Slidev deck in slides/:

cd slides
npm install    # first time only
npm run dev    # serves and opens http://localhost:3030

Keys: f fullscreen, o overview, arrows to navigate. All delivery cues live in the speaker notes — open http://localhost:3030/presenter for the presenter view. The display/code webfonts are fetched online (falls back to Georgia + system mono). npm run export renders a PDF.

The original reveal.js deck is parked in slides/legacy-reveal/ (open index.html in a browser) — delete it once the Slidev port has proven itself in rehearsal.

REPL — from the project root:

clj                # plain REPL, or:
clj -M:nrepl       # headless nREPL on :7888 — connect from Zed / CIDER / Calva

Then load a session file and evaluate the (comment ...) forms one by one. Evaluate, don't type — typing live under pressure eats minutes and momentum.

The hook — paste examples/console_lies.js into a browser DevTools console (not Node — the lie is DevTools lazy expansion), then expand the logged object after the mutation line runs.

File map

File	What it is	When
slides/slides.md	18 slides + 2 backup appendix slides (Slidev)	blocks 1–3
examples/console_lies.js	the console.log-that-lies demo behind slide 2	0:00
src/workshop/values.clj	identity vs equality, non-destructive updates, structural-sharing timings	0:25
src/workshop/data_oriented.clj	tickets dataset, core vocabulary, workload report, nested updates	0:30
src/workshop/macros.clj	code-is-data, unless, try-with vs with-open, building my->, macroexpand-1, (source ->), my-some->	0:50

Note: (source ->) and (source with-open) need a real JVM Clojure REPL (they read core sources from the classpath) — they won't work in babashka.

Timeline

Time	Segment	Where
0:00–0:05	Hook: the audit log that lies	slides 1–2
0:05–0:25	Two traditions → PLOP → values → structural sharing	slides 3–11
0:25–0:50	Live: values + data-oriented programming	values.clj, data_oriented.clj
0:50	One-slide breather: code is data	slide 12
0:50–1:10	Live: unless, try-with, my->, macroexpand, (source ->)	macros.clj
1:10–1:20	Features-as-libraries thesis → practice → adoption → resources	slides 13–16
1:20–1:30	Q&A buffer — don't plan content here	slide 17

Rehearsal notes

• Switch between deck and editor only at section boundaries — four switches total.
• Huge font in the editor, light theme, close every panel you don't need.
• If the live macro build stumbles: appendix slide A has all macroexpand outputs precomputed. Show, narrate, move on.
• The demo files carry no expected-result comments — you evaluate them live. The comments that remain are delivery cues: what to say, not what prints.
• Macro session runs long. try-with — the beat aimed squarely at the Java half of the room — now runs early, so it's safe. Cut from the tail instead: my-some-> (section 6, already flagged bonus), then with-timing (the generalization beat inside section 3).