[Haskell-cafe] ANN: HDBC v2.0 now available

[Niklas Broberg]

>> I really really think this is the wrong way to go. Occasional
>> destruction is desperately needed for progress, else things will
>> invariably stagnate.
>
> I disagree. Having everything fail (we measured it as ~90% of hackage)
> when people upgraded to ghc-6.10 would have been a disaster. Do you
> recall the screaming, wailing and gnashing of teeth after the release of
> ghc-6.8 when most of hackage broke? We (I mean ghc and cabal hackers)
> got a lot of flak for not making the upgrade process easier and
> needlessly breaking everyone's  perfectly good packages.

90%? That sounds like an awful lot for the relatively minor changes
with base-4. I guess a number of packages will use exceptions, and
others with use Data and Typeable, but 90%? I don't doubt you when you
say that you measured it though, just marvelling.

If 90% of hackage would truly break, then I agree that we might need
more caution than my radical approach. But I'm not fully convinced
there either. After all, unlike with the ghc-6.8 release, all that's
needed for a package to work again is to upload a new .cabal that
makes the dependency on base-3 explicit, if an author really doesn't
want to update the codebase. And even for those packages where library
authors don't do that simple step, all that's needed of the user of
the library is to specify the base-3 constraint when running
cabal-install.

My main complaint is really that there is currently no incentive
whatsoever for library authors to migrate. If we make base-4 the
default, it will require just a little bit of work to make packages
that depend on base-3 work anyway, as seen above. It's not so much
work that it should incur any screaming, wailing and teeth gnashing.
But it should be just enough work to encourage action in one way or
another, either truly migrating the code or just making the dependency
explicit as I noted above. I think it would be hard to find a more
accurate, and non-intrusive, incentive. :-)

I definitely agree with your suggestion to make hackage require an
upper bound on base. But that's to make us future proof, it won't
solve the issue here and now.

Cheers,

/Niklas