Clojure Zippers (2021)

Posted2 months agoActive2 months ago

prydt

111 points

7 comments

grishaev.meTechstory

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Debate

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ClojureFunctional ProgrammingData Structures

Key topics

Clojure

Functional Programming

Data Structures

The article provides a tutorial on Clojure Zippers, a data structure for navigating and manipulating tree-like data, and the discussion highlights its usefulness and potential applications.

Snapshot generated from the HN discussion

Discussion Activity

Light discussion

First comment

12h

Peak period

36-48h

Avg / period

2.3

Key moments

01Story posted
Oct 22, 2025 at 11:51 PM EDT
2 months ago
Step 01
02First comment
Oct 23, 2025 at 12:00 PM EDT
12h after posting
Step 02
03Peak activity
5 comments in 36-48h
Hottest window of the conversation
Step 03
04Latest activity
Oct 28, 2025 at 8:56 AM EDT
2 months ago
Step 04

Generating AI Summary...

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Discussion (7 comments)

Showing 7 comments

ngruhn

2 months ago

2 replies

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 months 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 months ago

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

clem

2 months ago

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

avbanks

2 months ago

This tutorial was extremely helpful, I was having a hard time grokking the power of zippers.

0_gravitas

2 months 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!

wry_discontent

2 months 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.

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ID: 45678001Type: storyLast synced: 11/20/2025, 12:41:39 PM

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