Hey, thanks for your interest.

Being able to include additional files is something I have considered many times, but have ultimately decided against and will not be adding as part of the language. My philosophy here is that importing files should be an application-level responsibility, and not that of the config format. From a technical standpoint, includes would add a level of I/O, which affects portability (this would not work in a WASM environment, for example).

This is something however you could absolutely implement yourself without too much difficulty. You could for example have a special _include key or similar, parse the referenced file(s), and mutate the main object to merge them in.

let {
  $imported = { _include = "path/to/extra.corn" }
} in {
  foo.bar = "baz"

  ..$imported
}

As for layers, I'm not sure I fully understand the request but I think the answer is the same - this is the responsibility of the application, or some higher-level library, and not the language itself. As you say, this is something the config crate can already handle.