> Besides, config languages never have the level of polish (re: tab completion and static analysis) that the main language does.

They don't have to!

> Why deny your users the niceties that you set up for yourself?

Don't do this, of course. :)

For instance, Nickel gained[1] an LSP implementation years before it hit version 1.0. When editing Nickel configs,byou get all the stuff you'd expect for a programming language: syntax highlighting, type hints, autocompletion, etc. But beyond static analysis, Nickel can also validate your configurations dynamically, according to arbitrary predicates-- and that too, integrates with your editor through the language server. Nickel ships with a command-line evaluator, REPL, pretty printer for data structures, code formatter, documentation generator, and CLI tab completions for Bash, zsh, Fish, PowerShell, and Elvish. Upstream distributes the tooling (which is, Go-style, a single executable with subcommands) as a Nix flake, a Docker image, and static executables for Linux aarch64 and x86_64 (< 30 MB, for now at least). Nickel doesn't yet have a package manager[3], but other than that it honestly has a better tooling story than many general-purpose programming languages currently in widespread use.

CUE, an older (but not old) configuration language (very cool in its own right), likewise has great tooling. It ships with a command-line evaluator, a pretty printer, a formatter, package management based on Go modules (i.e., it has both a `mod` and a `get` subcommand), a few refactoring tools, and tab completions for bash, zsh, and fish.[4] It currently lacks a language server[5] but there is recent and ongoing work to enable that.

There's no reason that a configuration language can't have first-rate tooling!

There is a new crop of really innovative, powerful configuration languages out there. I hope they start catching on.

> This way all your users are suitably placed on a slippery slope where one edit in the same language but to another file will transition them from user to contributor.

> Jail them in a separate language and they'll stay users forever.

This, I admit, deeply appeals to me. It's one of the things I really like about the Nix language, wart-y though it may be: the tools you use to configure your NixOS computer are the same ones you can go on to use to extend NixOS. I think that's an enormous strength.

But I also like for simple configuration to look really simple, and not trouble you much with the details of the language (or, God forbid, configuring the runtime). Perhaps programmable configuration languages, then, are good fits for tools like build systems and packaging systems (where the 'upstream' code users might next want to play with is also essentially fancy, expressive configuration in a special domain), but embedded DSLs might be better for applications (and work for packaging and build systems, too).

Re: creating a continuous road for users to hack on the software they use, GNU is really trying to do something special there: with Guix you have application configuration, package management, and system configuration handled in a DSL in Guile Scheme. But then Guix itself is also written in Guile! And at the same time, Guile is the official extension language of the GNU project, so GNU applications all (hopefully?) have Guile bindings, so you can use the same language to plug into (hopefully?) all the other GNU applications on your system. It's a cool idea.

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1: https://github.com/tweag/nickel/pull/405

2: https://www.tweag.io/blog/2024-05-16-nickel-programmable-lsp...

3: https://github.com/tweag/nickel/issues/1585

4: https://cuelang.org/docs/reference/command/

5: https://github.com/cue-lang/cue/issues/142