Instances for data types

[Sven Panne]

Playing around with System.Posix.Terminal, I realized that there are no Read,
Show, Eq, Enum, ... instances for the data types defined there (TerminalState,
TerminalMode, ...). This is not a very difficult problem to solve in one's
own program, but it's not very handy, either. This raises a general question:
What instances should be defined in the standard libraries for types like
this? A general policy would be a good thing. IMHO, at least Read, Show, Typeable
and Eq could be expected, having Ord, Enum and Bounded, too, would be nice.
Any opinions?

Cheers,
    S.