[Haskell-cafe] another instance of MonadError

David Feuer david.feuer at gmail.com
Thu Jul 14 22:24:12 UTC 2016

You can't do that; sorry. You can always turn a string into an IOException
if you like. Or you could write a wrapper around IO. But MonadError has a
functional dependency, so you can only have one error type per monad.

On Jul 14, 2016 6:19 PM, "Corentin Dupont" <corentin.dupont at gmail.com>

IO is an instance of MonadError IOException...
However I also need to make it an instance of MonadError String...
Is it possible?
I'm trying to instanciate this class:

class (Typeable n, Monad n, Applicative n, MonadError String n) => EvMgt n
where ...

instance EvMgt IO where...

Any idea?

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