Suppose, you want to implement a structured editor for some term type, so that the user can navigate through a given term and perform edit actions on subterms. In this case you are immediately faced with the problem of how to keep track of the cursor movements and the user's edits in a reasonably efficient manner. In a previous pearl G. Huet introduced a simple data structure, the Zipper, that addresses this problem. A drawback of the Zipper is that the type of cursor locations depends on the...