122. Introducing the Zipper data structure
The Zipper data structure is meant to facilitate cursor-like navigation capabilities over another data structure such as a tree. Moreover, it may provide capabilities for manipulating the tree like adding nodes, removing nodes, and so on.
The Zipper is created on the top of a tree and is characterized by the current position of the cursor and the current range or the current visibility area. At any moment, the Zipper doesn’t see or act on the entire tree; its actions are available only on a subtree or a range of the tree relative to its current position. The modification accomplished via the Zipper is visible only in this range, not in the entire tree.
In order to navigate and determine the current range, a Zipper must be aware of the tree structure. For instance, it must be aware of all the children of each node, which is why we start from an interface that must be implemented by any tree that wants to take advantage of a...
