Haskell Foldable Wats

Tue Mar 22 10:08:03 UTC 2016

Even better might be to use GHC 8 custom type errors in the constraint head
to explain what 'Impossible' means.

On Tue, 22 Mar 2016 10:21 am Henning Thielemann, <
lemming at henning-thielemann.de> wrote:

>
> On Wed, 24 Feb 2016, Chris Allen wrote:
>
> > You can't not-include the instances because we'll just end up with
> orphans so that's not cricket I think.
>
> We could define
>
>    instance Impossible a => Functor ((,,) a b) where
>
> where Impossible is a non exported class.
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