I'm trying to implement a functional interface to a tree. One of the standard things I can do is a zipper, which supports a single hole where the "focus" lives. (https://hkn.eecs.berkeley.edu/~dyoo/plt/zippers.txt)
However, as I understand it, zippers only support one "hole". One of the things I'd love to have is a zipper with multiple foci. The focused elements don't even necessarily have to be siblings. I'm trying to mimic the interface of a library like JQuery, which provides a way to select a collection of nodes at once; it makes certain tree manipulations really fun to do. I've seen mention of it in: http://stackoverflow.com/questions/3436559/zipper-like-data-structure-with-more-then-one-cursor, with a reference to Oleg's "Zippers with Several Holes" code at http://okmij.org/ftp/continuations/zipper.html#zipper2. Has anyone had experience implementing something like this? _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
