As Tomalak said in a comment, That’s like trying to create meaningful strings by walking the regex. It doesn’t work that way. A zipper helps you take a meandering walk through a structure, inspecting parts and optionally modifying them; in the end, you have the option of “zipping up” the zipper to get a modified … Read more
Let’s start with the Zipper-analog for lists. If you’d like to modify the nth element of a list, it takes O(n) because you have to copy the n-1 first elements. Instead, you can keep the list as a structure ((first n-1 elements reversed) nth element (remaining elements)). For example, the list (1 2 3 4 … Read more
Like the childcatcher in Chitty-Chitty-Bang-Bang luring kids into captivity with sweets and toys, recruiters to undergraduate Physics like to fool about with soap bubbles and boomerangs, but when the door clangs shut, it’s “Right, children, time to learn about partial differentiation!”. Me too. Don’t say I didn’t warn you. Here’s another warning: the following code … Read more
As this question is popping up regularly in the top of the “unanswered” list, let me just copy my comment as an answer here – nothing considerably more constructive has appeared since a year ago anyway. A List can be viewed as a comonad just as well (in multiple ways), while a Zipper can be … Read more
Funny that no one added lenses, since they were MADE for this kind of stuff. So, here is a CS background paper on it, here is a blog which touch briefly on lenses use in Scala, here is a lenses implementation for Scalaz and here is some code using it, which looks surprisingly like your … Read more