Thanks for the PR, for 1. your change kind of defeats the purpose of the example, with different names the nonrec keyword is no longer necessary and could be removed. It's necessary for the types to have the same name in order for this keyword to make sense.

I do not believe the example is an error, but could be one, or perhaps a warning based on your compilation settings: https://sketch.sh/s/p5Bc8Y3L8qoufPo7jxhlGe/

Oh, thanks for responding.
I notice that this example works fine with the repl but gives a compilation error when running yarn build. Same with OCaml (utop works fine while ocamlc gives an error). The following code fixes it:

type t = string;
module M = {
  type nonrec t = list(t);
};