Proposal: Add common instances for Control.Applicative.Const

Edward Kmett ekmett at
Mon Oct 14 23:43:31 UTC 2013

Alternately we could just hand-roll the instances so it doesn't change
whether it gets imported if the user writes

import Control.Applicative (Const(..))

but I agree with simplifying the presentation.

On Mon, Oct 14, 2013 at 5:03 PM, Ross Paterson <R.Paterson at>wrote:

> On Mon, Oct 14, 2013 at 09:33:38AM -0700, Eric Mertens wrote:
> > It would be handy for Control.Applicative.Const to have the various
> derivable
> > instances (Eq, Ord, Read, Show).
> >
> > In particular Read and Show would make debugging easier.
> I'd suggest redefining getConst as a function rather than a field to
> make the derived Read and Show instances simpler.  Ditto WrappedMonad.
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