I'm kind of unclear what module signatures would be since Julia lets code define modules at runtime, so I don't think this could be meaningfully defined for Julia.

Maybe a better link is Clojure Spec and Racket module contracts.

https://clojure.org/about/spec

https://docs.racket-lang.org/reference/contracts.html

https://docs.racket-lang.org/style/Units_of_Code.html

For most intents and purposes one can use a (potentially Singleton) type passed as a argument to functions instead of a module containing functions. And doing that gets you all the tooling and power you could want. (But probably in a different way to you want it). Since multiple dispatch takes care of that.

You can compare and contrast MLDatasets.jl (uses submodule per dataset) vs CorpusLoaders.jl (uses a extra type argument per dataset)