Union serialization provider for F#

UnionStringSerializer.fs

let UnionToString (u: 'a) =
    match FSharpValue.GetUnionFields(u, typeof<'a>) with
    | case, _ -> case.Name

let StringToUnion<'a> (s: string) =
    match FSharpType.GetUnionCases typeof<'a> |> Array.filter (fun case -> case.Name = s) with
    | [| case |] -> FSharpValue.MakeUnion(case, [||]) :?> 'a
    | _ -> failwithf "Unable to parse %A" s

type UnionStringSerializer<'a>() =
    inherit SerializerBase<'a>()

    override this.Deserialize(context, args) =
        match context.Reader.GetCurrentBsonType() with
        | BsonType.String -> context.Reader.ReadString() |> StringToUnion
        | other -> failwithf "Unable to parse %A" other

    override this.Serialize(context, args, value: 'a) =
        context.Writer.WriteString <| UnionToString value

BsonSerializer.RegisterSerializer(UnionStringSerializer<MyType>())