On Wednesday 23 February 2011 09:58:56, Yves Parès wrote: > I am using mtl-2. Importing Control.Monad.Error doesn't work, I have > to explicitly import Control.Monad.Instances.
Weird. Control.Monad.Error imports Control.Monad.Instances (), so it ought to be visible. What exact versions of mtl, base, GHC are you using? > > 2011/2/22 Daniel Fischer <daniel.is.fisc...@googlemail.com>: > > 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. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
