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

6 May 2010


      Joachim Breitner  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)?

-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic@gmail.com
IvanMiljenovic.wordpress.com