On Sun, Sep 12, 2010 at 20:46, Tillmann Rendel <ren...@mathematik.uni-marburg.de> wrote: > Paolo Giarrusso wrote: >> in a tracker entry you linked to, >> http://hackage.haskell.org/trac/hackage/ticket/704, duncan argues that >> "we also want to be able to do things like linking multiple versions >> of a Haskell package into a single application". [snip] > Even with the technical ability to link all of foo, bar, pair-1 and pair-2 > together, I don't see how this program could be reasonably compiled. > Therefore, I think that the notion of consistent install plans is relevant > semantically, not just to work around some deficiency in the linking system.
Your case is valid, but OTOH there other cases to support: if I link together two programs which use _internally_ different versions of regex packages, cabal should support that - and here I guess we agree. The issue is how to express or recognise the distinction. I had this kind of scenario in mind, and that's why I proposed using versioned typenames for typechecking - your example program would then be caught as ill-typed. However, that's not enough, because the correct solution is to use the same pair version. - OTOH, Program would probably have its own cabal file, which could maybe list a dependency on pair. But I don't like this solution - the developer shouldn't have to do this. - The nicer alternative would be to extract, from the types used in the .hi files, whether they mention pair at all - like here, and unlike the case when the different packages are used internally. This solution is perfect but takes extra work which I can't estimate. Actually, some more work would maybe be needed to cope with cross-module inlining, but I believe that this can be done by cabal, by just "looking at" .hi files, without further changes to GHC - after versioned typechecking is introduced if missing, anyway. And maybe some interface to .hi files should be exposed. -- Paolo Giarrusso - Ph.D. Student http://www.informatik.uni-marburg.de/~pgiarrusso/ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
