[Haskell-beginners] Debugging overlapping instances (mtl vs
paolo.losi at gmail.com
Thu Sep 9 04:35:29 EDT 2010
I'm definitely stuck with the migration of my project
from mtl to transformers. The use of transformer is
mandated by a new dependency that I need to add.
Overlapping instances for Monad (Either String)
arising from a use of `tstampToForecasts'
instance (Control.Monad.Trans.Error.Error e) => Monad (Either e)
-- Defined in Control.Monad.Trans.Error
instance Monad (Either e)
-- Defined in mtl-18.104.22.168:Control.Monad.Error
I really have no clue of who and why is bringing mtl instance in the
If I compile the file directly with:
ghc -package monads-tf -package transformers -hide-package mtl
I can successfully compile the module, so it seems the problem
is not specific to that module. But the compilation fails
if I do ghc -package monads-tf -package transformers -hide-package mtl
What's the best practice to debug this problem?
What are the constraints of indirectly depending on both mtl
I'm really stuck :-/
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