[Haskell] Read Instances for Data.Map and Data.Set

[Christian Maeder]

Johannes Waldmann wrote:
> Georg made the point that if a type is an instance of Show,
> then it should also be an instance of Read, and  read . show == id

That does (hopefully) happened now.

> I'd like to repeat my earlier point that it would be better
> if the user of the type can decide whether he wants
> some predefined Show/Read instances or roll his own.

It is really not an option (in current Haskell) to put Show/Read 
instances in a separate module. Just consider if you want to combine a 
couple of module were two modules rely on different instance 
implementations. (A horror if you want to share code)

IT is, however, an option to add auxiliary (non-overloaded) utility 
functions for showing and reading (parameterized of some separators).

Cheers Christian