Hi Sergei,
I think you should use {-# OVERLAPPABLE #-}: see the description here
https://ghc.haskell.org/trac/ghc/ticket/9242#comment:16 which is probably
in the manual somewhere too.
Regards,
Adam
On Thu, May 21, 2015 at 9:40 AM, Sergei Meshveliani
People,
I wrote recently about finding places to set {-# OVERLAPPING #-} when porting an application from 7.8.2 to 7.10.1.
I am doing this for porting docon-2.12 from 7.8.2 to 7.10.1.
And ghc-7.10.1 indeed helped me to find several places to set this pragma (instead of using the total key -XOverlappingInstances).
Finally, it has come to this module:
--------------------------------------------- Preprocessing library docon-2.12.1... [48 of 86] Compiling ResRing__ ( ResRing__.hs, dist/build/ResRing__.o )
ResRing__.hs:183:31: Overlapping instances for Eq (Maybe PropValue) arising from a use of ‘/=’ Matching instances: instance Eq a => Eq (Maybe a) -- Defined in ‘GHC.Base’ instance (Residue r, Eq a) => Eq (r a) -- Defined in ‘ResEuc0_’ In the expression: lookup IsGxBasis ps /= Just Yes ... ----------------------------------------------
As before, I set instance {-# OVERLAPPING #-} (Residue r, Eq a) => Eq (r a) where ...
in ResEuc0_.hs.
But this does not help, the compiler continues with the same report.
I see the difference to previous porting process in that one of the overlapping instances is of the GHC library, so that I cannot set the needed overlap pragma for it.
On the other hand, ghc-7.8.2 compiled docon-2.12 successfully.
What my be a way out?
Thanks,
------ Sergei
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