[Haskell-cafe] Introducing Instances in GHC point releases

[John Goerzen]

So this is annoying (CCing -cafe)

I need NominalDiffTime and UTCTime to have Typeable instances.  In
6.10.1, they didn't ship with them out of the box, so I added them.
Apparently, in 6.10.3, they DO ship with those instances out of the box.

Annoyingly, that means that my code breaks on 6.10.3.

Even more annoyingly, __GLASGOW_HASKELL__ is still 610, so I can't even
work around this via cpphs.  There appears to be no way to make code
that requires those Typeable instances work with both 6.10.1 and 6.10.3.

Yet another reason to avoid API incompatibilities in point releases.

Does anybody have an idea on the best way to handle this?

-- John

Don Stewart wrote:
> convertible appears broken with 6.10.3. Any thoughts?
> 
>     Writing new package config file... done.
>     Downloading convertible-1.0.1...
>     Configuring convertible-1.0.1...
>     Preprocessing library convertible-1.0.1...
>     Preprocessing executables for convertible-1.0.1...
>     Building convertible-1.0.1...
>     [1 of 8] Compiling Data.Convertible.Base ( Data/Convertible/Base.hs, dist/build/Data/Convertible/Base.o )
>     [2 of 8] Compiling Data.Convertible.Utils ( Data/Convertible/Utils.hs, dist/build/Data/Convertible/Utils.o )
>     [3 of 8] Compiling Data.Convertible.Instances.Map ( Data/Convertible/Instances/Map.hs, dist/build/Data/Convertible/Instances/Map.o )
>     [4 of 8] Compiling Data.Convertible.Instances.Num ( Data/Convertible/Instances/Num.hs, dist/build/Data/Convertible/Instances/Num.o )
>     [5 of 8] Compiling Data.Convertible.Instances.C ( Data/Convertible/Instances/C.hs, dist/build/Data/Convertible/Instances/C.o )
>     [6 of 8] Compiling Data.Convertible.Instances.Time ( Data/Convertible/Instances/Time.hs, dist/build/Data/Convertible/Instances/Time.o )
> 
>     Data/Convertible/Instances/Time.hs:61:9:
>         Duplicate instance declarations:
>           instance Typeable NominalDiffTime
>             -- Defined at Data/Convertible/Instances/Time.hs:61:9-32
>           instance Typeable NominalDiffTime
>             -- Defined in time-1.1.3:Data.Time.Clock.UTC
> 
>     Data/Convertible/Instances/Time.hs:64:9:
>         Duplicate instance declarations:
>           instance Typeable UTCTime
>             -- Defined at Data/Convertible/Instances/Time.hs:64:9-24
>           instance Typeable UTCTime
>             -- Defined in time-1.1.3:Data.Time.Clock.UTC
>     cabal: Error: some packages failed to install:
>     HDBC-2.1.0 depends on convertible-1.0.1 which failed to install.
>     convertible-1.0.1 failed during the building phase. The exception was:
> 
>