bcl VS dhall-lang

Another take on replacing HCL with something more sensible:

BCL https://github.com/wkhere/bcl

I agree with you that HCL sucks when it comes to variables.

Other thing that is funny: no user-defined functions, being unable to use function calls in string interpolations, but allowing variables... so it is like saying: we have this parser and at some points it allows expressions, at some other point not. This seems wrong.

At the same time I agree or at least understand original author's intent to squeeze HCL to maxinum. There is something appealing in HCL visual form, at least when defining resources. Maybe it's just (almost) simplest form of defining such structures that can exists.

This is why I started to work on my own format for configuration, visually similar but with different model of evaluation.

Here is the first attempt: https://github.com/wkhere/bcl

Disclaimer: I named it BCL, 'B' stands for Basic, to somehow relate to HCL and make it easily pronounced. But later I discovered that another BCL is used as Google to configure the Borg platform and seems to be massively hated ;) So I look for the better name..

I am crafting BCL, own configuration language.

https://github.com/wkhere/bcl

I started this when I was unable to squeeze certain usage patterns from HCL, like: variables living in the same scope as the file, evaluating variables in one pass with parsing, easily using external (environment) variables; plus, a simplified syntax.

The implementation is mostly done: you can defined blocks holding key-value pairs and use numerical, string and bool expressions in them. I will add lists and nested blocks.

At this very moment I am rewriting a parser from yacc-based to a Pratt top-down parser with vm, heavily inspired by the excellent book "Crafting Interpreters".

https://github.com/wkhere/bcl

Will not immediately help for all of YAML usages, but at least for defining resources in a Terraform-like style. In fact, it's already it's already helpful as a replacement for HCL in one internal project, that was a final motivation to hack it.

In a bigger picture, I have no idea how to help with YAML omnipresence in Kubernetes. More than a half of my problems in a $daily_job is how crude is consolidating a final Helm chart from different sources. I am not saying that Helm would be inherently a bad tool or my company has chosen pretty bad way of using it - I guess everyone is doing their best considering the ciscumstances. But manipulating textual templates is just too error prone, and the detection of errors happens too late. I dare to say - Kubernetes would do much better with custom format based on a C-like syntax, instead if trying to prove how cool YAML is, especially when it isn't.

Related:

just few days ago I crafted together some ideas i had couple of years already for a configuration language, syntactically like HCL but without HashiCorps idiosyncrasies.

Here it goes, BCL (_Basic_ Configuration Language, for a lack of better name yet), Go prototype, I can code Python port and possibly several other as well..

https://github.com/wkhere/bcl

Fail to see how this is any different than Dhall (https://dhall-lang.org/) other than it produces plists too.

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)

There are underpowered languages / tools, that can only solve a problem for which they are intended poorly. But not all limited tools are like that.

Say, eBPF is prominently not Turing-complete, which allows to guarantee that a eBPF program terminates, and even how soon. Still eBPF is hugely useful in its area.

Or, say, regular expressions are limited to regular languages; in particular, they famously [1] cannot process recursive structures, like trees. Still tools like grep / ag / rg are mightily useful.

Yes, I agree that YAML is underpowered for proper k8s configuration! But it's also too powerful for its own good in other aspects [2]. I wish Google used Dhall [3] or their own purely functional config language (FCL? I already forgot the name) instead of YAML; sadly, they did not.

[1]: https://stackoverflow.com/a/1732454/223424

[2]: https://ruudvanasseldonk.com/2023/01/11/the-yaml-document-fr...

[3]: https://dhall-lang.org/

Dhall: Dhall is a programmable configuration language that combines features like JSON, functions, types, and import capabilities. Its style leans towards functional programming, so if you're familiar with functional-style languages such as Haskell, you might find Dhall to be quite intuitive.

I've been thinking along these lines but more 'strongly validated' than statically typed in the sense that you'd be better off being able to load the entire config and then produce a list of problems (and should be able to offer good editor support if done correctly).

Though https://dhall-lang.org/ demonstrates that you can statically type quite a lot of configuration to great advantage, which appears to be programmatically embeddable in multiple languages per https://docs.dhall-lang.org/howtos/How-to-integrate-Dhall.ht...

> Where practical is in the sense of an engineer (or in their terms, a CS practitioner),

Configuration processing. E.g. I'd like my yamls to be decidable, though I'd settle for guaranteed to halt[1].

[1] https://dhall-lang.org/

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

And to checkout Dhall: https://dhall-lang.org/