Re: Proposal: add -XPolyKinds to Data.Monoid

Ah yeah. I remember when we moved it. We just accidentally lost the PolyKinds along the way. Should be easy enough to fix. On Mon, Jul 14, 2014 at 2:51 PM, adam vogt wrote:

The example works with ghc-7.6.3. It looks like https://github.com/ghc/ghc/commit/1d1ff77aaa09efaddc8cfe0dcf92d6763297cf11 is to blame.

On Mon, Jul 14, 2014 at 12:37 PM, Carl Howells wrote:

...

At the moment, the Monoid instance for Data.Proxy.Proxy is only defined for types with kind *.

Prelude Data.Proxy Data.Monoid> (Proxy :: Proxy String) <> Proxy Proxy Prelude Data.Proxy Data.Monoid> :set -XDataKinds Prelude Data.Proxy Data.Monoid> (Proxy :: Proxy 5) <> Proxy

<interactive>:8:20: No instance for (Monoid (Proxy 5)) arising from a use of ‘<>’ In the expression: (Proxy :: Proxy 5) <> Proxy In an equation for ‘it’: it = (Proxy :: Proxy 5) <> Proxy

Enabling -XPolyKinds while compiling the Data.Monoid module is the only change necessary to make the Monoid instance for Proxy polykinded like Proxy itself is. I don't believe adding a language pragma would have any other effect on that module, and I believe the only effect of changing that instance would be allowing more correct programs to compile.

This is my first proposal to this list, so I'm starting with something that I hope isn't controversial. Let me know if I should do anything different procedurally in future proposals.

Thanks. _______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries

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