cel-spec VS starlark

My employer uses a combination of Protocol Buffers (for the config schema definition) and Bazel/Starlark (for concrete instantiations). Configs are validated at build time and runtime using CEL (https://github.com/google/cel-spec).

The Common Expression Language (CEL) implements common semantics for expression evaluation, enabling different applications to more easily interoperate. https://github.com/google/cel-spec

Looks like Google invented a specification for a simple "expression language." -> https://github.com/google/cel-spec/blob/master/doc/langdef.md. Writing the expressions feels like writing Java, C++, Go, or TypeScript code. Google then released C++ and Go versions of this langauge as a library.

https://github.com/google/cel-spec unfortunately, it's in Go or C++. Of course I can write a binding to them. But is there any other similar that you would know of for Java? My other course of action would be to offload computation to another service using this library in Go, or Jsonnet or Open Policy Agent/Rego based evaluation, which I'd prefer not to. Executing JS in Java via Nashorn also an option but it'd be heavy weight.

Having a standard way to share expressions does seem quite useful, especially when it's multilingual.

[0]: https://github.com/google/cel-spec

There's more information about CEL and its specifications here

Especially when dealing with more complex match rules, I personally much prefer Caddy's matchers over building some weird-ass if constructs in Nginx. It also supports CEL for request matching, giving you access to extremely powerful logic, if you need it.

The implementations and users page mentioned above:

https://github.com/bazelbuild/starlark/blob/master/users.md

Starlark: Starlark is a language for describing build transformations, inspired by Python, but with features that make it suitable for embedding in software like Bazel. It can be used for configuration generation due to its capability for deterministic evaluation and expressing complex build transformations.

In the design of Starlark (https://github.com/bazelbuild/starlark), I often had to push back against new feature requests to keep the language simple. I explicitly listed simplicity as a design goal.i

Of course, the scope of the language is not the same as general purpose languages, but there's always pressure from the users to add more things. I also think many people underestimate the cost of adding new features: it's not just about adding the code in every compiler/interpreter, specifying every edge-case in a spec, updating all the tooling for the language and writing tutorials; it's also a cost on everyone who will have to read any of the code.

one of the benefits of starlark (unlike python): "Starlark is suitable for use in highly parallel applications. An application may invoke the Starlark interpreter concurrently from many threads, without the possibility of a data race, because shared data structures become immutable due to freezing." from https://github.com/bazelbuild/starlark/blob/master/spec.md - it's not python, you can't do recursion (!) and it's more limited (you can't read a file in bazel, and parse it, you have to make this operation into the graph somehow)

You can do the same in Bazel which uses Starlark for its BUILD files. Starlark is a dialect of Python so it makes it super easy to work with.

Make sense. We do not use Python actually, the build language is starlark, which is the config lang used by bazel. https://github.com/bazelbuild/starlark

Have you seen Starlark? It's not too far from that, but safer in a number of ways: https://github.com/bazelbuild/starlark