Instances for data types

[Malcolm Wallace]

> > 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. 
> 
> Good point.  I've been meaning to create a separate document so we have
> somewhere to collect general library policies like this.  It's on my
> whiteboard...

And I agree that Sven's suggestion would be a good policy.  i.e.
    Eq, Show, Read, Typeable
should always defined as instances, and
    Ord, Enum, Bounded
should be defined as instances if they make sense for this type.

Regards,
    Malcolm