library reorganisation

[Simon Marlow]

Einar Karttunen wrote:
> I think it would be nice to have implementation dependent code (GHC.*)
> and implementation independent code in separate packages. Currently
> there is no way to know whether a Cabal package depending on base
> wants Data.List or GHC.Something.

Right, base shouldn't expose anything from GHC.*, and we should have a 
separate package that does provide these interfaces.

However, I don't think this is at all easy to arrange.  The lowest 
package would then be 'ghc', with 'base' on top (it can't be the other 
way around, because 'base' is implemented using 'ghc').  Furthermore, 
'ghc' would contain a lot of implementation independent parts, simply 
because a lot of GHC.* modules use things like Data.List.  And there are 
recursive dependencies between GHC.* and other implementation-indepenent 
modules.  This doesn't look terribly practical, I'm afraid.

I just had an interesting idea though: if a package could re-expose 
modules from a dependent package, then we could provide a new view of 
the base package with the GHC.* modules hidden.  This is tantalising, 
because it seems easy to implement... I must think about this some more.

Cheers,
	Simon