I would wager it's actually all implemented with immutable data structures; maybe with some advanced version of zippers [0]. [0] https://en.wikipedia.org/wiki/

I would wager it's actually all implemented with immutable data structures; maybe with some advanced version of zippers [0]. [0] https://en.wikipedia.org/wiki/Zipper_%28data_structure%29 https://en.wikipedia.org/wiki/Zipper_%28data_structure%29