[Haskell-cafe] Use MySQL from Haskell

[Björn Peemöller]

Maciej Podgurski schrieb:
> So I switched to HDBC-2.1.1 and got the next compile error:
>
> Building convertible-1.0.5...
>
> Data/Convertible/Instances/Num.hs:671:0:
>     warning: no newline at end of file
> [...]
> [5 of 8] Compiling Data.Convertible.Instances.C (
> Data/Convertible/Instances/C.hs, dist\build/Data/C
> onvertible/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:64:0:
>    Duplicate instance declarations:
>      instance Typeable NominalDiffTime
>        -- Defined at Data/Convertible/Instances/Time.hs:(64,0)-(65,42)
>      instance Typeable NominalDiffTime
>        -- Defined in time-1.1.3:Data.Time.Clock.UTC
>
> Data/Convertible/Instances/Time.hs:67:0:
>    Duplicate instance declarations:
>      instance Typeable UTCTime
>        -- Defined at Data/Convertible/Instances/Time.hs:(67,0)-(68,34)
>      instance Typeable UTCTime
>        -- Defined in time-1.1.3:Data.Time.Clock.UTC 

Hi Maciej,

this is quite easy to fix (although a little bit dirty). The problem is
that time-1.1.3 now defines some Typeable instances which time-1.1.2.4
did not and which are therefore defined in convertible, too. I don't
know a general fix to the problem, but you can either

- download the convertible package and comment out the two instance
declarations as shown in the error message and then cabal install it
- install from Hackage with additional constraint: cabal install
convertible --constraint=time<1.1.3

I hope this will help you get HDBC running.

Cheers,
Björn