I am using mtl-2. Importing Control.Monad.Error doesn't work, I have
to explicitly import Control.Monad.Instances.
2011/2/22 Daniel Fischer
On Tuesday 22 February 2011 23:07:05, Yves Parès wrote:
Hello,
When importing Control.Monad.Error, it shows me that (Either e) is an instance of MonadFix, but not an instance of Monad. Isn't there a problem?
Prelude Control.Monad.Error> :i Either data Either a b = Left a | Right b -- Defined in Data.Either instance (Eq a, Eq b) => Eq (Either a b) -- Defined in Data.Either instance Monad (Either e) -- Defined in Control.Monad.Instances instance Functor (Either a) -- Defined in Control.Monad.Instances <snip> instance MonadFix (Either e) -- Defined in Control.Monad.Fix <snip>
Works right here. With mtl-1.*, there's an (Error e) restriction on the instances.