Re: [Haskell-cafe] another instance of MonadError

I could also do my own MonadError class also, no? However this doesn't work: {-# LANGUAGE ConstraintKinds #-} type EvError a = MonadError String a class (Typeable n, Monad n, Applicative n, EvError n) => EvMgt n where ... instance EvMgt IO where... How can I create a new class "EvError" that inherits all the functions of "MonadError String"? On Fri, Jul 15, 2016 at 12:24 AM, David Feuer wrote:

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" wrote:

Hello, 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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