That approach is too brittle for my taste. An annotator writer would declare a type that is meant to be a singleton, but there's no way to enforce this. One careless annotator that creates a second instance of such a type, and the whole analysis chain stops working. With my approach, at least the bar is a bit higher.
Well, with FsVariables, one careless annotator can still set the variable to a new value and break downstream annotators. There can even be name conflicts with two annotators trying to use the same variable name for different things. It's OK with me to not implement my suggestion because it encourages annotator developers to rely on undeclared assumptions (that only a single instance of a type exists) - basically the same criticism I had of the FsVariable proposal. In that case let's leave things the way they are. I don't think this is a pressing problem that needs to be addressed. -Adam
