That technique sounds analogous to using a zipper to traverse a list (I've found a decent looking link for the technique if you're interested - https://ferd.ca/

That technique sounds analogous to using a zipper to traverse a list (I've found a decent looking link for the technique if you're interested - https://ferd.ca/yet-another-article-on-zippers.html https://ferd.ca/yet-another-article-on-zippers.html)