proposal #4095: add Applicative instance for Either

Ross Paterson ross at
Tue May 25 14:02:15 EDT 2010

On Tue, May 25, 2010 at 07:55:42PM +0200, Bas van Dijk wrote:
> On Tue, May 25, 2010 at 7:21 PM, Ross Paterson <ross at> wrote:
> > Fine by me.  Making it a non-orphan would break Haskell 98 compatibility,
> > though.
> Making it non-orphan means moving the Monad Either instance to either
> GHC.Base (which defines the Monad class) or to Data.Either (which
> defines the Either type). How exactly does this break Haskell 98
> compatibility?

This Haskell 98 module will not be accepted:

module M where
instance Monad (Either a)

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