MTL Upgrade Problem

[Dominic Steinitz]

Hi, I have

> dom1 at fourier:~/asn1_0> ghc-pkg list --user
> /home/dom1/.ghc/i386-linux-6.12.1/package.conf.d
>    mtl-1.1.0.2
>    mtl-2.0.1.0
>
But I get the following error:

> [4 of 6] Compiling LatticeMod       ( LatticeMod.hs, interpreted )
> [5 of 6] Compiling ConstraintGeneration ( ConstraintGeneration.lhs,
> interpreted )
>
> ConstraintGeneration.lhs:781:6:
>     Overlapping instances for Monad (Either String)
>       arising from a use of `return'
>                    at ConstraintGeneration.lhs:(781,6)-(782,69)
>     Matching instances:
>       instance (Error e) => Monad (Either e)
>         -- Defined in Control.Monad.Trans.Error
>       instance (mtl-1.1.0.2:Control.Monad.Error.Class.Error e) =>
>                Monad (Either e)
>         -- Defined in mtl-1.1.0.2:Control.Monad.Error
>     In the expression:
>         return
>           (ExtensibleConstraint
>              (ResStringConstraint v top) (ResStringConstraint top top) b)
>     In the definition of `pvPermittedAlphabetElements':
>         pvPermittedAlphabetElements (S (SV v)) b
>                                       = return
>                                           (ExtensibleConstraint
>                                              (ResStringConstraint v top)
>                                              (ResStringConstraint top top)
>                                              b)
> Failed, modules loaded: ASNTYPE, LatticeMod,
> Language.ASN1.PER.Integer, Language.ASN1.PER.IntegerAux.
If I do

> dom1 at fourier:~/asn1_0> ghc-pkg hide mtl-2.0.1.0

Then the error goes away. But if I do

> ghc-pkg hide mtl-1.1.0.2

Then I still get the error.

Is there a wiki page that tells me what to do to upgrade from mtl-1 to
mtl-2? Or perhaps someone can tell me what to do?

Many thanks, Dominic.