[Haskell-cafe] GHC 7/Cabal request for help

[Erik Hesselink]

I've just tested this, and with GHC 7, cabal chooses QuickCheck 2.4,
whereas with GHC 6.12, it chooses 2.1. If I specify that 6.12 should
choose 2.4 as well, I get the same issue there. This is to be
expected, because I don't see the CPP checks you mentioned in
Test/QuickCheck/Instances.hs in testpack-2.0.1. Perhaps you haven't
released a version with those checks yet?

Erik

On Thu, Mar 24, 2011 at 14:18, John Goerzen <jgoerzen at complete.org> wrote:
> Hi folks,
>
> I don't have a GHC 7 environment running yet (it's on my list...) but I
> received a bug report pointing me at this build failure:
>
> http://hackage.haskell.org/packages/archive/testpack/2.0.1/logs/failure/ghc-7.0
>
> Among other things, this noted:
>
> Dependency QuickCheck >=2.1.0.3: using QuickCheck-2.4.0.1
>
> and the errors were:
>
> [1 of 3] Compiling Test.QuickCheck.Instances (
> src/Test/QuickCheck/Instances.hs, dist/build/Test/QuickCheck/Instances.o )
>
> src/Test/QuickCheck/Instances.hs:39:10:
>    Duplicate instance declarations:
>      instance Arbitrary Word8
>        -- Defined at src/Test/QuickCheck/Instances.hs:39:10-24
>      instance Arbitrary Word8 -- Defined in Test.QuickCheck.Arbitrary
>
> src/Test/QuickCheck/Instances.hs:42:10:
>    Duplicate instance declarations:
>      instance CoArbitrary Word8
>        -- Defined at src/Test/QuickCheck/Instances.hs:42:10-26
>      instance CoArbitrary Word8 -- Defined in Test.QuickCheck.Arbitrary
>
> Now, that's fairly standard, and in fact, in my code, is wrapped with:
>
> #if MIN_VERSION_QuickCheck(2,3,0)
>    -- we have Word8 instances here
> #else
> instance Arbitrary Word8 where
>    arbitrary = sized $ \n -> choose (0, min (fromIntegral n) maxBound)
>
> instance CoArbitrary Word8 where
>    coarbitrary n = variant (if n >= 0 then 2 * x else 2 * x + 1)
>                where x = abs . fromIntegral $ n
> #endif
>
> And that code has been working to support modern QuickCheck versions for
> some time.
>
> It would appear that something in Cabal, GHC 7, or QuickCheck is breaking
> this check.
>
> Ideas?
>
> -- John
>
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