On Sun, Oct 23, 2011 at 06:56:57PM -0400, Britt Anderson wrote:
I wanted to try reactive, but cabal install fails on checkers (a dependency). Here is a portion of the error message, there are other overlapping instances that follow. Can someone advise me how to proceed. Thank you.
[13 of 15] Compiling Test.QuickCheck.Classes ( src/Test/QuickCheck/Classes.hs, dist/build/Test/QuickCheck/Classes.o )
src/Test/QuickCheck/Classes.hs:137:38: Overlapping instances for Show (a -> b) arising from a use of `property' Matching instances: instance Show (a -> b) -- Defined in Text.Show.Functions instance Show base:System.Event.Manager.IOCallback -- Defined in base:System.Event.Manager
This is very naughty of System.Event.Manager, to define IOCallback as a *type synonym* for a certain function type, and then declare a Show instance for it. However, the instance shouldn't come into play unless System.Event.Manager is imported, and I don't think it is. So this error message seems rather odd to me. What version of GHC do you have? What is the output of 'ghc-pkg list' and 'ghc-pkg check'? -Brent