Kai Devlog #3: Custom DSL & Plugin Modules

Something that is bred into kai‘s bones is the idea that if something is hard to use, it won’t be used unless it must be. In the last devlog we made kai modular in that you could build your own plugins, but there were several problems:

• You had to write custom parsing logic (terrible!)
• They weren’t strict definitionally and the concept of a Backend was unclear and vague (does that just mean nix? What if there is more than one requirement?)
• They were unvalidated. You could “do whatever you wanted” and received no help from xkai when you did something illogical
• Plugin modules themselves were not modular/reusable/easy to make

This release now updates that so the plugins should be much simpler to write, parsing is handled for you, a few validations are done by xkai to help ensure you built it right, and Backend was given a much stronger definition that represented the system much better.

Additionally, I made a custom DSL! Even though the previous embedded roc DSL was pretty thin, I realized I could make things much simpler if I made a custom one. The primary motivation to do it in an embedded language was to inherit things like conditional logic, but I really only needed it for switching between systems (e.g. if system == linux then install ...) and that alone did not justify the extra complexity. Plus, it would require every user to have both a determinate system installed like nix and the roc compiler. Instead, we remove that extra 30MB or so and the final kai binary comes out to about 600KB! This does come at the cost of a lot of gutsy config parsing and validation, which is annoying, but I think the tradeoff is worth it.

But the best part is now, the simplest config.kai (which I’ll soon rename Kaifile) looks like this:

shell {
    pkgs: ["cowsay"]
}

With just this, you’ll be able to define reproducible dev environments! For changing behavior on different systems:

on linux {
    shell {
        pkgs: ["cowsay"]
    }
}

on macos {
    shell {
        pkgs: ["pokemonsay"]
    }
}

Much simpler and straightforward than a flake.nix, that’s for sure!

Onward!