> I don't get it. Why is Long the problem? It looked to me like the issue was > Set, but I really can't see why Set and List every would have matched, so I > don't see why this ever worked. > > Looks like I need a Scala matching tutorial :-(
Looks like *I* need a Scala tutorial ;-) You're right again, I should have read the message more carefully. Apparently, the compiler will issue an error message if we check for Full(EmptySet), but not if it's a non-empty instance of Set... go figure.
