[Haskell-cafe] containers-deepseq?

Michael Snoyman michael at snoyman.com
Tue Nov 29 09:36:54 CET 2011

On Tue, Nov 29, 2011 at 10:29 AM, Joachim Breitner
<mail at joachim-breitner.de> wrote:
> Hi,
> Am Dienstag, den 29.11.2011, 07:43 +0200 schrieb Michael Snoyman:
>> Since the release of deepseq 1.2, we've had a bit of a problem: when
>> using the newest versions of packages on Hackage, there is no NFData
>> instance available for the containers types. When GHC 7.4 comes out
>> with its newer version of containers, this will be addressed, but
>> we'll still have problems for users of older GHC releases.
>> I'd like to suggest a solution: a new package called
>> containers-deepseq. Using conditional compilation, it will provide an
>> orphans NFData instance for all containers types when deepseq >= 1.2
>> and containers < 0.5. Packages (e.g., aeson) would then depend on
>> containers-deepseq and simply import the module whenever they rely on
>> the NFData instances. When GHC 7.4 comes out, the package will
>> essentially be a no-op.
>> Does this make sense?
> from a distro point of view: Please void this if possible; every
> additional package causes us work. (Although we’d likely just not
> upgrade containers before 7.4.1 and patch out the dependency in the
> cabal file when we switch to 7.4.1.)
> Why can’t you put the instances in containers, guarded by some #ifs? I
> don’t see the point of a separate package for these 15 lines of code.

Because containers cannot be updated: you're stuck with whatever
version comes with GHC.


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