nickel VS jsonnet

So, its key features are:

1. domain-specific: designed for conveniently creating and composing derivations. This reason alone already justifies a new language, or an embedded domain-specific language (such as the Guile/Scheme for guix), or a mix of both (Starlark, the build language of Bazel embedded in a restricted Python-variant).

2. purely functional: this ties well into the philosophical backing of Nix the package manager, which aims to be purely functional, also known as hermeticity in other build systems (Bazel).

3. lazily evaluated: similar to other build systems (including Bazel), so that you can build only what you need on demand.

4. dynamically typed: this one is controversial. Being dynamically typed—in other words, not developing a type system—gets Nix out of the door first. But users often complain about the lack of proper types and modularity. There are experiments to address this, such as Nickel (https://github.com/tweag/nickel).

It is understandable that a one-pager may not have space for the whys.

Nickel：Nickel is a straightforward configuration language aimed at automatically generating static configuration files. Essentially, it's akin to JSON with the addition of functions and types.

Also look at nickel which is an evolution of nix. It's my favorite in this space.

nickel-lang.org

https://github.com/tweag/nickel

Or this https://github.com/tweag/nickel

Nickel is a programming language. While HCL is just a configuration format, so not really comparable.

Here's a comparison with similar tools: https://github.com/tweag/nickel#comparison

As for 'providence', I suppose you meant provenance :) it's been delayed because this was less critical for 1.0 to decide on or to implement (as it: it doesn't break backward compatibility in any way to add this feature in the short term), but this is very much on the roadmap: Issue #235. That's a must-have in a language with merging like Nickel.

Have you considered using a different language for templating? this could be a BIG selling point. Some good ones are cue-lang (though I haven't seen support for rust), kcl or nickel-lang.

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.

[Language: Jsonnet] (on GitHub)

Maybe you'd like jsonnet: https://jsonnet.org/

I find it particularly useful for configurations that often have repeated boilerplate, like ansible playbooks or deploying a bunch of "similar-but" services to kubernetes (with https://tanka.dev).

Dhall is also quite interesting, with some tradeoffs: https://dhall-lang.org/

A few years ago I did a small comparison by re-implementing one of my simpler ansible playbooks: https://github.com/retzkek/ansible-dhall-jsonnet

Apologies for the lack of context, and for missing this comment until today.

Both are tools for defining kubernetes manifests (which are YAML) in a reusable manner.

Jsonnet is a formally specified extension of JSON. It’s essentially a functional programming language (w/some object oriented features) that generates config files in JSON/YAML/etc, so it’s straightforward to determine whether an input file is valid, and to throw an error that points to an exact line if it’s not. It has a high learning curve, especially for people whose only experience is with imperative languages.

https://jsonnet.org/

Helm charts also generate YAML/JSON config files, but they use Go templating. This is easier and faster to understand, since it’s mostly string substitution and not much logic (there’s conditionals, iterators, and very basic helper functions). Unfortunately a simple typo or mistake can cause errors that are difficult to diagnose (the message may indicate a problem far away in code from the actual mistake). It can also generate output that’s valid according to the string templating rules, but not what was intended, which can be very confusing to debug.

Despite these shortcomings, the vast majority of kubernetes applications are distributed as helm charts. I understand why things ended up this way, but I still wish it were more common for people to invest the upfront effort to learn the superior tool, so it could be more widespread.

I like Google's Jsonnet [1], which has all of this except for 4.

Jsonnet is quite mature, with fairly wide language adoption, and has the benefit of supporting expressions, including conditionals, arithmetic, as well as being able to define reusable blocks inside function definitions or external files.

It's not suitable as a serialization format, but great for config. It's popular in some circles, but I'm sad that it has not reached wider adoption.

[1] https://jsonnet.org/