[kvb]

It's very nice to be able to check annotations in a build step. I'm just saying that adding language-external checks makes it fairly meaningless to say that "C#" supports it; would it be fair to say that C# supports all of Haskell's features if I require annotating C# constructs with Haskell code and then use a modified Haskell compiler in a post-build step to verify that the pieces are composed in a valid way? None of this is to say that the C# code you linked to is not useful - it's just not possible to use "vanilla" C# to achieve what "vanilla" F# can do.

To your later question, while F# and OCaml share a common core, there's lots of F# code that won't compile as OCaml and vice versa, and units of measure are one such example. The syntax for measure-annotated types is not valid OCaml syntax.