immer VS clj-kondo

I've been working on an editor (not text) in C++ and pretty early got into undo/redo. I went down the route of doIt/undoIt for commands but that quickly got old. There was both the extra work needed to implement undo separately for every operation, but also the nagging feeling that the undo operation for some operation wasn't implemented correctly.

In the end, I switched to representing the entire document state using persistent data structures (using the immer library). This vastly simplified things and implementing undo/redo becomes absolutely trivial when using persistent data structures. It's probably not something that is suitable for all domains, but worth checking out.

https://github.com/arximboldi/immer

How does this compare to https://github.com/arximboldi/immer (other than the C/C++ difference)?

Also, it's my understanding that, in practice, persistent data structures require a garbage collector in order to handle deallocation when used in a general-purpose way. How does your implementation handle that?

You might be interested in ewig and immer by Juan Pedro Bolivar Puente:

https://github.com/arximboldi/ewig

https://github.com/arximboldi/immer

See the author instantly opening a ~1GB text file with async loading, paging through, copying/pasting, and undoing/redoing in their prototype “ewig” text editor about 27 minutes into their talk here:

https://m.youtube.com/watch?v=sPhpelUfu8Q

It’s backed by a “vector of vectors” data structure called a relaxed radix balanced tree:

https://infoscience.epfl.ch/record/169879/files/RMTrees.pdf

That original paper has seen lots of attention and attempts at performance improvements, such as:

https://hypirion.com/musings/thesis

https://github.com/hyPiRion/c-rrb

You’re absolutely right, however people have been putting in the “extra efforts” required for efficiency. Check out immer if you’re interested.

The C++ immer library: https://github.com/arximboldi/immer

For C++ check this one out - https://github.com/arximboldi/immer

Yeah I agree that I should link that wikipedia page in the docs, I'll do that as soon as I get a chance. immer (https://github.com/arximboldi/immer) also links that page in its docs, for the exact same reason I'm sure. Interestingly, there is a lot of overlap between persistent data structures in the functional programming sense and persistent data structures in the persisted-to-disk sense because persistent data structures in the FP sense are one of the best ways to guarantee atomic updates and safe failure recovery in a persisted-to-disk system! Btrfs and ZFS, as well as many databases, are at their core basically just copy-on-write B+ trees.

I’ve never tried it, but I love the idea of implementing editor scene state using immutable data structures like https://github.com/arximboldi/immer With that, every edit would append a new node to a list of scene states. Undo/redo becomes iterating your view of the scene up and down through that list. Can’t screw up an undo function if there’s never any work to do :P

I have! I think it's related to the C++ immer library which I used several years ago in Vortex. It's kinda like the previous generation of ValueScript. 🍻

My best suggestion here would be clj-kondo with flycheck-clj-kondo in Emacs. I really can't recommend it enough and would have killed to have it when I was learning Clojure. Not only will it underline all of those references to (now) undefined vars, but it can tell you about numerous little mistakes like mixing up arguments orders in (say) sequence functions, misplaced docstrings that get discarded, style conventions, etc. It's staggering how good it is even for a language as dynamic as Clojure.

The clj-kondo linters are worth reading.

Sure!

Spec: https://github.com/edn-format/edn

Example (linter config): https://github.com/clj-kondo/clj-kondo/blob/634294183a0aa2ca...

Clj-kondo doesn't produce an AST but you could easily combine the analysis output with the AST produced by rewrite-clj by matching on location.

But if you want full support, you can implement a hook: https://github.com/clj-kondo/clj-kondo/blob/master/doc/hooks.md

Please configure and use tools like clj-kondo and kibit. Kibit will report areas where you could write idiomatic clojure instead. Eg, it should catch all those (if (condition) true false) and ask you to replace it with (condition). Or if you really need a boolean value, use boolean to coerce it.

Try clj-kondo, a Clojure linter which will tell you about arity errors and more, before you even evaluate your code.