immer VS deprecated-coalton-prototype

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. 🍻

can't jerk

I used to use CL quite a bit, but have since abandoned it for Haskell, so I'm a bit biased.

There's a number of issues with that:

- I'd be missing all the optimizations that can be performed due to purity.

- There's more to Haskell's type system than just vanilla Hindley-Milner, and the implementation of it isn't particularly trivial. https://github.com/stylewarning/coalton is the closest thing and it's still missing a large amount of the type system.

- Doing the implementation would be a significant amount of work to get it to integrate well with the language, and it would be a layer tightly glued on top instead of integrated with the language.

- A major part of Haskell is the standard library, a good chunk of the semantics of Haskell people use on a day to day basis, like monads and etc, are a part of the standard library.

This looks like something Common Lisp does better, however I have too little Clojure experience to compare. CL (and SBCL in particular) does "good enough" static type checks, it throws warning at compile time (when we compile one function with a keystroke). We can also precise our function types gradually. It isn't a HM type system (Coalton[1] could be it) but it's already great (compared to no compile-time types at all).

Oh, about interactive development: that's sure, CL shines here. Objects get updated (lazily) after a class change, we can install Quicklisp libraries without restarting the image, etc. It's very smooth.

1: https://github.com/stylewarning/coalton

Help out with Coalton.

If you like this kind of stuff, maybe you can help implement type classes in Coalton.

(there's a work-in-progress library to add a dialect of ML on top of CL: coalton)