recursion-schemes VS jsonnet

I've got another article planned where I talk through exactly why and how this function works, but it's worth noting that I didn't come up with it myself -- I simply ported it from the Haskell library that first introduced this technique.

Reasonably proud of my part 2 solution, although would like to try using a recursion scheme rather than unstructured recursion:

Yeah, that project is pretty much at the bottom of my list, unfortunately. My top projects these days are mgmt, klister, recursion-schemes, and hint... And that's already too much!

In a programming context, recursion schemes can be used to write recursive (or corecursive) functions, by automating/abstracting away the common boilerplate part of actually doing the recursion. They take the form of polymorphic higher-order functions, which can be imported from a library like this classic one.

Maybe I didn't link the best post. It is unfortunately the only one I know that uses Rust. If you are able to read Haskell, the documentation for the recursion-schemes package might be a better resource?

Writing something as a type of fold over an infinite sequence is nicer than using recursion directly in my opinion. See: https://hackage.haskell.org/package/recursion-schemes

Consider recursion schemes! It let's you separate the logic of how your recursion is structured on your data, and the logic of what you're doing on each recursion stage. So e.g. you can write the core logic of a recursive linked list summation as just fun x accum -> x + accum, and then you just find the appropriate recursion scheme to pipe the list values into x and handle recursing to build accum (a catamorphism in this case)

It's a pretty complicated bug, documented in details at https://github.com/recursion-schemes/recursion-schemes/issues/50

It’s also trivial and easy in Haskell — you just need an instance of `Foldable` or `Traversable` on your collection, and then you can fold or traverse it in a configurable way. Or for recursive structures, use https://hackage.haskell.org/package/recursion-schemes. Or even just pass a traversal function as an argument for maximum flexibility.

https://hackage.haskell.org/package/recursion-schemes is the "normal" library for this type of generalized folding. It even contains Base instances for Maybe and Either.

OK, what we can do now? Use a preprocessing language guaranteed to produce valid syntax, like Jsonnet for json? That wil work, for sure. However, you have now a friction problem: it's new file format that requires implementing its own toolchain (Jsonnet is not json, so editor add-ons, parsers, interpreters, libraries, etc.) and you will need to drive the team through the learning curve of a language with its own syntax and semantic. Will you implement a serious project... or will you have a coffee break at that point, and keep doing things the same old way?

https://jsonnet.org/ I never heard of this before. This seems like the JSON I wish I really had. Of course at some point you could just use JavaScript.

I've been reading the book Modern Compiler Implementation in ML lately. It's been helpful to brush up on some concepts while developing Tsonnet (my typed-aspiring Jsonnet flavor) and I hope to learn a ton more. However, I'm growing dissatisfied with some details -- not specifically the book, but the choice of the development environment.

For the past 2 years, I've been working extensively with Jsonnet, a configuration language that augments JSON and helps eliminate repetition in our config files. It has its limits (many by design), which keeps the language simple to use. But there's one thing that keeps nagging at me when I'm deep in the code: what's the shape of the input or output of this function? And wouldn't it be great if we could type objects and completely ditch those validators checking value types? Having a compiler handle all that would be sweet. I'm not alone here – I've talked to plenty of folks who'd love this feature too.

Kubernetes does not provide or require a configuration language like Jsonnet, as it provides a declarative API that can be used with different types of declarative specifications.

jsonnet[1] and kapitan[2] are the tools I currently use. Their learning curve is not optimal (and I tried to contribute to smoothen it with a jsonnet course[3] and a 'get started wit kapitan' blog post[4]), but once used to it it's hard to do without, and their combination makes them even more useful (esp. if you deploy K8s).

In Ruud's case, Jsonnet might have been worth looking at as Hashicorp tools can be configured with json in addition to HCL. But that would have been less fun I guess ;-)

I hope for Ruud it finds its niche, there's quite some competition in this field!

1: https://jsonnet.org/

Kubernetes config is a decent example. I had ChatGPT generate a representative silly example -- the content doesn't matter so much as the structure:

https://gist.github.com/cstrahan/528b00cd5c3a22e3d8f057bb1a7...

Now consider 100s (if not 1000s) of such files.

I haven't given Pkl an in depth look yet, but I can say that the Industry Standard™ of "simple YAML" + string substitution (with delicate, error prone indentation -- since YAML is indentation sensitive) is easily beat by any of:

- https://jsonnet.org/

- https://nickel-lang.org/

- https://nixos.org/manual/nix/stable/language/index.html

- https://dhall-lang.org/

- (insert many more here, probably including Pkl)

jsonnet cli: link

Jsonnet: A data template language implemented in C++, suitable for application and tool developers, can generate configuration data and organize, simplify and manage large configurations without side effects.