It was chosen to be implemented as a generic type in this design because the way that uncertainty "pollutes" underlying values maps well onto monads which were expressed through generics in this case.

> And why does it need to be part of the type system?

As presented in the article, it is indeed just a library.

> What if I want Bayesian?

Bayes is mentioned on page 46.

> And why does it need to be part of the type system? It could be just a library.

It is a library that defines a type.

It is not a new type system, or an extension to any particularly complicated type system.

> Am I missing something?

Did you read it?

https://www.microsoft.com/en-us/research/wp-content/uploads/...

https://github.com/klipto/Uncertainty/

> Bayes is mentioned on page 46.

Bayes isn't mentioned in the linked article. But thanks for the links.

That did not surprise me because I did not think the article was about anything but about adapting the dot-net library they linked to on Microsoft's site to swift, and I figured that if I wanted to understand the library and the approach I had better read the links that indicated I might be able to learn from them.

I don't think inference is part of this at all, frequentist or otherwise.

It's not part of the type system, it's just the giry monad as a library.