Has anyone ever done a Schema language for validating and parsing
S-expressions? I've been trying to look for one for a couple months and
haven't found anything.

Something lightweight similar to JSON Schema
(<https://json-schema.org/>) would be nice. Maybe Racket's optional type
specs or Clojure's spec could be adapted for this purpose? I've only
scratched the surface of those systems.

There's some preliminary schema work for Clojure's EDN dialect of
S-expressions:

* <https://github.com/edn-format/edn/issues/40>
* <https://github.com/miner/herbert>

I'd have an immediate need for a Schema language for Schemedoc work. If
we find a suitable language we could write a SRFI and/or libraries for it.