Proposal: Add Data instance for Const

[Edward Kmett]

Definitely an oversight.

On Wed, Nov 2, 2016 at 11:40 AM, Ryan Scott <ryan.gl.scott at gmail.com> wrote:

> GHC Trac #12438 [1] exists because there's no Data instance for Const
> in base. I found this quite surprising, since we have Data instances
> for just about every other type combinator out there (Identity, Sum,
> Product, Compose, etc.), but not for Const. The fix for #12438 would
> be quite simple: I propose we add
>
>     deriving instance (Data a, Data b) => Data (Const a b)
>
> to Data.Data in base. Any objections?
>
> Ryan S.
> -----
> [1] https://ghc.haskell.org/trac/ghc/ticket/12438
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