Clojure Zippers (2021)

Summary

Part 1. The Basics of Navigation In this article, we will discuss zippers in the Clojure language. These are an unusual way to work with collections. Using a zipper, you can traverse a data structure arbitrarily and modify its content as well as search in it. A zipper is a powerful abstraction that pays off over time. However, it is not as straightforward as regular tools and requires training to deal with. Let’s talk about a zipper in simple terms. It is a wrapper that offers a variety of data manipulations. Let’s list the main ones: moving vertically: down to children or up to a parent; moving horizontally: left or right among children; traversal of the entire data structure; adding, editing and deleting nodes. This is a partial list, and you will see the most interesting solutions more later. Note: these capabilities are available when working with arbitrary data, whether it’s a combination of vectors and maps, XML, or a tree. This makes zippers a powerful tool. If you figure out how to handle them, you will boost your skills and open new doors. The good news is that zippers are available in the base Clojure package. It’s better than a third party library that needs to be included. Zippers are easy to add to a project with no fear of license issues or new dependencies. Clojure zippers harness the power of immutable collections. Technically, a zipper is a collection that stores data and the position of the pointer. Together they are called a location. A step in either direction returns a new location, just like the assoc or update functions generate new data from old data. From the current location, you can get a node, that is, a piece of data that the pointer refers to. Let’s clarify their difference to avoid confusing beginners. Location is the source data and the position in it. Moving around the location generates a new location. From the location, you can retrieve a node — the data that is in this area. Below is an example with the vector [1 2 3]. To move to ...