Re: proposal #4095: add Applicative instance for Either

On Tue, May 25, 2010 at 7:59 PM, Henning Thielemann wrote:

On Tue, 25 May 2010, Bas van Dijk wrote:

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On Tue, May 25, 2010 at 7:21 PM, Ross Paterson wrote:

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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?

Since there is no Monad Either instance in Haskell 98, Haskell 98 programs can safely define their own one. If we would add such an instance to the base library this would break those programs.

Oh yes I see. Bummer! Bas