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

On Thu, Mar 24, 2011 at 9:30 AM, Erik Hesselink wrote:

I've just tested this, and with GHC 7, cabal chooses QuickCheck 2.4, whereas with GHC 6.12, it chooses 2.1.

I believe that the behavior you're seeing is because the package selection is biased by the state of your local package databases (plural, because there is a separate db for each version of GHC). If quickcheck 2.1 was installed with ghc 6.12, and satisfies the package requirements, then cabal won't select a newer version on its own (at least, that's my understanding). If you either didn't have QuickCheck installed in your ghc7 package db, or had v.2.4 installed, then ghc 7 would use that version. Building with cabal-dev instead of cabal will use the most recent set of satisfying dependencies according to your local hackage index, rather than the compiled versions of packages you happen to have around. Alternatively, you can ghc-pkg unregister all the dependencies from your local package db. (in this case, ghc-pkg unregister QuickCheck-2.1, with ghc-pkg from 6.12, then cabal-install testpack and you should see the failure). --Rogan

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 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-...

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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