Polyglot Corner: Bouncing Ball, Three Lisps

You just built a bouncing ball in JVM Clojure (exercises/phase_1/bouncing_ball.clj). Here's the exact same idea, already built, in the other Lisp dialects this course's sibling repos use. You don't need to understand every line yet - just notice how much of the shape survives the jump: init/tick/draw, an immutable world value, the same raylib calls underneath.

Jolt (native Clojure, Chez Scheme, no JVM)

bounce.clj in raylib-jlt: a bouncing ball with IsKeyPressed-driven pause and an on-screen DrawFPS counter. Jolt calls raylib with zero C shim code at all, it exploits real ABI facts about how C passes small structs (you'll learn exactly how in Phase 3).

Run it yourself with cd raylib-jlt && bb bouncing-ball. Two prerequisites, both of which that repo checks for you rather than failing mysteriously:

  • Jolt v0.7.23 or newer (jolt --version). Older versions can't express the by-value struct bindings the suite now uses, and fail at compile rather than at runtime. If you don't have it: brew install jolt-lang/jolt/jolt, or curl -sL https://raw.githubusercontent.com/jolt-lang/jolt/main/install | bash, or nix run against its flake. The prebuilt binary is self-contained — runtime, compiler and stdlib in one executable — and wants glibc 2.35+ on Linux x86_64 or macOS 14+ on arm64. On an Intel Mac, musl/Alpine, or older glibc you'd be building from source, which is a bigger errand than this optional aside is worth: read bounce.clj instead and carry on.
  • libraylib 6.0 or newer — bb lib:check verifies it and bb lib:install installs it. This one is worth the check: raylib 6.0 changed DrawCircleGradient's signature without changing the symbol name, so a 5.5 library links happily and then draws in the wrong place.

That second point is worth a moment, because this course is on the other side of it. libs/ here ships raylib 5.5, and the engine's own draw-circle-gradient! is bound to 5.5's signature — so the two suites are each correct against the raylib they carry, and installing 6.0 for raylib-jlt does not disturb this repo, which loads its bundled 5.5 in preference to anything on your system. Two versions of the same C library, side by side, is a normal thing to end up with; what makes it survivable is that each caller is explicit about which one it wants.

Once you have a Jolt REPL open, (doc some-fn) works there the way it does in Clojure — doc, find-doc, apropos and dir all landed in Jolt v0.7.21. source and pst don't, so reading raylib.clj is still how you find out what a binding actually does.

jank (native Clojure, C++/LLVM, no JVM)

b12n-raylib-jnk's bouncing-ball port, same idea, a completely different FFI philosophy: jank draws the line at the value, not the call. A native raylib value can't leave the function that created it without being explicitly boxed first. You'll build this same ball again, deliberately, in Phase 3's comparative module.

What's identical, what's not

  • Identical: the shape of the program. Every one of these has an init, something that runs every frame to move the ball, something that draws it, and a loop that ties them together.
  • Not identical: how each dialect talks to raylib's C code underneath. JVM Clojure (what you're using) goes through JDK's Panama FFI. Jolt and jank each have their own answer, with real trade-offs - that's the whole subject of Phase 3.

Next

Phase 2: Arcade Classics: time to build something with an actual win/lose condition.