[Haskell-cafe] Mixing mtl- and transformers-using libraries

[Joachim Breitner]

Hi,

Am Donnerstag, den 06.05.2010, 22:42 +1000 schrieb Ivan Lazar
Miljenovic:
> Joachim Breitner <mail at joachim-breitner.de> writes:
> > I have a rather large project here that uses standard mtl stuff. This
> > program now wants to use salvia, which in turn uses the transformers
> > library. The result is this:
> >
> > X.hs:163:29:
> >     Overlapping instances for Monad (Either String)
> >       arising from a use of `neuePersonCommit' at X.hs:163:29-48
> >     Matching instances:
> >       instance (transformers-0.1.4.0:Control.Monad.Trans.Error.Error e) =>
> >                Monad (Either e)
> >         -- Defined in transformers-0.1.4.0:Control.Monad.Trans.Error
> >       instance (Control.Monad.Error.Class.Error e) => Monad (Either e)
> >         -- Defined in Control.Monad.Error
> >
> > Is there any way of using salvia without having ghc consider instances
> > from transformers?
> 
> Switch to using transformers yourself (I believe it's API compatible
> with mtl)?

I tried, but other dependencies still use mtl, still both instances are
in scope.

Greetings,
Joachim

-- 
Joachim "nomeata" Breitner
Debian Developer
  nomeata at debian.org | ICQ# 74513189 | GPG-Keyid: 4743206C
  JID: nomeata at joachim-breitner.de | http://people.debian.org/~nomeata
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