Your first two cases are equivalent to the `Some(o) => o` case; the syntax I used was a bit ad-hoc but the following F# typechecks: let join_option oo =

Your first two cases are equivalent to the `Some(o) => o` case; the syntax I used was a bit ad-hoc but the following F# typechecks: let join_option oo = match oo with | Some(o) -> o | None -> None