[Haskell-beginners] Builds with cabal, but not with GHC

[Brent Yorgey]

On Wed, Sep 28, 2011 at 03:03:33PM +0000, Amy de Buitléir wrote:
> 
> Test.hs:20:9:
>     No instance for (mtl-1.1.1.1:Control.Monad.Error.Class.MonadError
>                        CPError (ErrorT CPError IO))

I don't know a solution, but just want to point out that this error
message smacks of inconsistent package versions being used.  Something
else used mtl-1.1.1.1 and the current module is being compiled with a
different version of mtl, or something like that.  Hopefully this can
provide a fruitful direction of investigation...

-Brent