Here's my own attempt at implementing a somewhat readable copying GC in C - https://github.com/matp/tiny-lisp/blob/master/tiny-lisp.c#L1...

Cool, that's an interesting solution! I tried hard to keep the GC implementation as straight-forward as possible, as a teaching aid, but I'll admit that debugging the GC was a bit of a struggle when roots weren't clearly indicated as such.

I made a Ruby version [0] in case anyone is interested.

[0] https://github.com/matp/himawari