[Haskell-cafe] Re: Proposal: register a package as providingseveral API versions

[Simon Marlow]

Claus Reinke wrote:

>> It could be done using the tricks that Claus just posted and I 
>> followed up on.  You'd need a separate package for hsFoo-2 that 
>> specifies exactly which bits of hsFoo-3 are re-exported.  Given some 
>> Cabal support and a little extension in GHC, this could be made 
>> relatively painless for the library maintainer.
> 
> are those tricks necessary in this specific case? couldn't we
> have a list/range of versions in the version: field, and let cabal
> handle the details?

I don't understand what you're proposing here.  Surely just writing

version: 1.0, 2.0

isn't enough - you need to say what the 1.0 and 2.0 APIs actually *are*, 
and then wouldn't that require more syntax?  I don't yet see a good reason 
to do this in a single .cabal file instead of two separate packages.  The 
two-package way seems to require fewer extensions to Cabal.

> aside: what happens if we try to combine two modules M and N
> that use the same api A, but provided by two different packages
> P1 and P2? say, M was built when P1 was still around, but when
> N was built, P2 had replaced P1, still supporting A, but not necessarily 
> with the same internal representation as used in P1.

Not sure what you mean by "try to combine".  A concrete example?

Cheers,
	Simon