I think the CL implementations must have happened when I was away from the forum. Wart started out as a common lisp implementation of arc: http://arclanguage.org/item?id=12814; https://github.com/akkartik/wart/tree/sbcl. But again, I did this without ever grokking conditions and restarts. The OP was actually quite illuminating for me.
Though, I'd probably end up implementing something closer to wat.js with the arc library.
What was the reason pg decided not to go with CL for the base of arc? I remember seeing him say it somewhere...
I'm not sure why he changed it though. There must have been some benefit (maybe the lisp-1 vs lisp-2) which made it easier to write arc.