Clojure Zippers (2021)

7 comments

• 0_gravitas 3 days ago

  I've been using Clojure for a few years now and zippers have always been a blindspot (had no idea even _when_ they would be useful), this is a remarkable tutorial!

• ngruhn 2 days ago

  I'm not sure if I get it. But I don't know Clojure syntax too well. Say I want to represent a slideshow state. I could do it with

      { 
        slides: List<Slide>, 
        current_index: Int
      }
  

  Or alternatively:

      {
        left_slides: List<Slide>,
        current: Slide,
        right_slides: List<Slide>
      }
  

  Is it fair to call the latter a Zipper?
  [-]
  • shakadak 2 days ago

    Yes, although it's usually defined as:

        {
          slides_shown: List<Slide>,
          slides_left: List<Slide>
        }
    

    Where the head of slides_left is the current slide. Pretty much any recursive data structure can be derived into a zipper.
  • laszlokorte 2 days ago

    Yes if List is immutable and the interface for stepping through the slides ist designed accordingly

• clem 2 days ago

  I've used zippers to edit parse trees. Very useful API, if a little user unfriendly.

• wry_discontent 2 days ago

  I've used zippers a couple times.

  Once for navigating a collection of deeply nested routes in a webapp, and once for navigating deeply nested xml to grab very particular data.

  Both times it was pretty pleasant and nice to use.

  I wouldn't reach for them in most normal situations cause they're more complicated to get right than simple looping (or `clojure.walk/prewalk`), but if you have large semi-predictable data structures, you can do cool stuff with zippers.

• CNNCultists 2 days ago

  [flagged]