how far would "if you DEPENDS on FOO, and FOO is =m, you can only be =m or =n" get us?I guess it depends on the (use-)case. But in general I'd like a system like that, especially if it would spew out warnings and errors for cases like the one mentioned.
or are there hidden traps on this?
(the hard case is if a non-tristate DEPENDS on a tristate, but... that's a trap anyway)