Adding Applicative/Functor instances to all Monads in GHC

Ian Lynagh ian at
Fri May 17 20:48:47 CEST 2013

Hi David,

On Fri, May 17, 2013 at 08:32:09PM +0200, David Luposchainsky wrote:
> > [Maybe] this would be better discussed on the ghc-devs@ list
> I thought that as well, but SPJ said this might be a better place, as it
> mostly concerns the base libraries. Since the discussion started here, I
> think we shouldn't change lists. (Maybe if individual problems arise
> those could be discussed individually over there.)

Ah, so you're talking about the GHC code /and/ all of the libraries that
come with GHC?

I'd be in favour of adding the instances to the libraries.

> Suppose 7.8 includes all instances as proposed, and we're going up to
> 7.14 in a couple of years, and 8.0 introduces the new hierarchy.
> Everything down to 7.8 will be compilable by 8.0

No, it won't. Unrelated to this proposal, you can't build GHC version X
with GHC version Y, where Y > X.

Ian Lynagh, Haskell Consultant
Well-Typed LLP,

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