> let notAValue: string | null = null

When did F# get unions?

Damn. It's only for nulls: https://github.com/fsharp/fslang-design/blob/main/RFCs/FS-10...

Wonder if they will generalize: https://github.com/fsharp/fslang-design/blob/main/RFCs/FS-10...

At least they chose a syntax that makes it possible to generalize, which is a smart choice imho :)

Yeah it looks a lot like Python's PEP 604[0].

[0] https://peps.python.org/pep-0604

It had it since the first version as far as I know.

You're probably referring to Disciminated unions aka sumtypes? That's not what the parent meant

I thought those are the same and I realize that there is a difference.