Ok, I haven't blogged for a while ....
First of all, thanks a lot to Peter Sestoft for providing me these wonderful nullable types test cases :-)
After playing around with it for a while, I think I finally got the grammar right. At least, it's now passing a full bootstrap-world and from a look at the grammar, we're also not allowing `?' at places where they don't belong. However, I just have a very basic skeleton: the more complex things like converting from or to a nullable type are not there yet.
Unfortunately, I had to realize that you can do very weird things with nullable types, like Foo<int?[]?>?.
I've also done some bug-fixing the last two weeks and cleaned some of the GMCS-related bug reports in bugzilla. Some are still there, and sometimes it's really hard to tell how difficult a bug is until you actually sit down to fix it. My main challenge for next week are nullable types, but if I find the time, I'll also do some more bug fixing.