I am a bit late to this discussion, but do recall using a the rosezipper in HaRe. And I just took a look and recall doing some experiments with zippers, which are at https://github.com/alanz/HaRe/tree/98f390b6e9d48537429863ca890aa853afcd7c79/... The actual code I used for the move definition refactoring is at https://github.com/alanz/HaRe/blob/98f390b6e9d48537429863ca890aa853afcd7c79/... I added a couple of helper functions too. I am sure it is all horrible code, I was learning at the time, and it sort of blew my mind. Alan On Wed, 22 Jul 2020 at 21:11, Olaf Klinke wrote:

...

A direct implementation without using a library is interesting, thank you. I refrained from doing that, because I thought that Control.Zipper would actually do this for me. Actually, I was pretty successful with using Control.Zipper to change node labels, but failed doing more complicated stuff.

Isn't that a strong indicator that zippers are an improper abstraction for your purpose? Perhaps after rolling your own implementation you can more easily discover how to represent the algrorithm as a zipper.

Olaf

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