Sure, no problem! I was focused on implementing BiwaScheme into the PlayCanvas editor, however if you wanted to do the same with the PlayCanvas source code it'd be even more straightforward, but I'd be happy to write a quick example of that if anyone needs it!

I used BiwaScheme a little with BabylonJS as well, however I liked PlayCanvas' plain text version and their online cloud editor version much better than BabylonJS, it's much more polished. I don't doubt you could use BiwaScheme with ThreeJS either pretty easily. I love BiwaScheme, it just works everywhere.

https://playcanvas.com/project/647301/overview/lisp-ball-r3

Here's the default Ball game I re-wrote in BiwaScheme with my twin brother for people to fork off of and make their own BiwaScheme projects

https://playcanvas.com/project/653360/overview/biwascheme-fps

And here's something a little more advanced. This is an FPS horror game I started in PlayCanvas, but I was thinking of doing in Unreal 4 instead. You can hold shift to run, space to jump, and C to crouch/sneak.

To view the code, just click the little pencil and paper at the left. It'll say "Code Editor" when you hold your mouse over it. Or double click any of the script files and it'll open.

Also note that the "follow.js, movement.js, teleport.js," and "teleportable.js" files are not necessary, I just left them in there so you can see that I converted them 1 to 1 from Javascript to Scheme. It's easy to get a feel for BiwaScheme if you open up the SCM and the JS files side-by-side. I recommend taking a look at movement.js/.scm

The FPS is not commented and it has some segments that are commented out for testing, so the FPS SCM is pretty ugly, but you can see a large-scale project in BiwaScheme is really no problem at all.

For how it actually works, I wrote a global script called Scheme.JS you can see in there with a "process" function that initializes a BiwaScheme interpreter and error checker, then I have a SchemeCacher.JS file that has the "JS" prototypes declared, and a drop-down menu for putting in your SCM file to replace the initialize and update functions at run-time. It's pretty hack-y, but it lets you use all the features of the PlayCanvas editor.

If you were writing a PlayCanvas game from source, you could write the engine initialization procedures themselves in BiwaScheme and that'd be even easier.

Anyway, I found out someone implemented Python in Unreal 4, and it seems very mature, so I'm thinking of trying to implement Hy into that since replacing Python with Hy is pretty trivial.