The last time I saw this error, it was because the package database was messed up (there was an instance of MonadIO in scope, but it was for the wrong package.) However, I don't know what the source of the problem is here.
Edward Excerpts from i hamsa's message of 2014-07-20 08:26:52 +0100: > I was trying to upgrade to ghc-7.8 the other day, and got this > compilation failure when building ghc-mtl-1.2.1.0 (see the end of the > message). > > I'm using the haskell overlay on Gentoo Linux straight out of the box, > no local cabal installations of anything. > > Now I was told that other people can compile ghc-mtl with 7.8 just > fine, so there must be something broken in my specific configuration. > What would be an effective way to approach the situation? > > In the sources I see that an instance of MonadIO GHC.Ghc does exist. I > don't understand these errors. Are there multiple different MonadIO > classes in different modules? > > Thank you and happy hacking. > > Now the errors: > > Control/Monad/Ghc.hs:42:15: > No instance for (GHC.MonadIO Ghc) > arising from the 'deriving' clause of a data type declaration > Possible fix: > use a standalone 'deriving instance' declaration, > so you can specify the instance context yourself > When deriving the instance for (GHC.ExceptionMonad Ghc) > > Control/Monad/Ghc.hs:46:15: > No instance for (MonadIO GHC.Ghc) > arising from the 'deriving' clause of a data type declaration > Possible fix: > use a standalone 'deriving instance' declaration, > so you can specify the instance context yourself > When deriving the instance for (MonadIO Ghc) > > Control/Monad/Ghc.hs:49:15: > No instance for (GHC.MonadIO Ghc) > arising from the 'deriving' clause of a data type declaration > Possible fix: > use a standalone 'deriving instance' declaration, > so you can specify the instance context yourself > When deriving the instance for (GHC.GhcMonad Ghc) > _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
