Arg has unlawful instances

Edward Kmett ekmett at
Sat May 11 07:35:18 UTC 2019


I agree with Henning on this one.

(==) provides an equivalence relation.

Despite the addition of some vocabulary in base 4.12 about how (==)
"should" be structural, that is at odds with Arg's actual purpose.

I'd rather argue that the attempted refinement of (==)'s documentation was
rather overzealous than that Arg as it is defined is wrong.

The instances are useful and follow the intent of the classes, just not the
extra paragraph that was bolted on sideways to the text describing Eq.


On Sat, May 11, 2019 at 9:30 AM Henning Thielemann <
lemming at> wrote:

> On Fri, 10 May 2019, David Feuer wrote:
> > There also needs to be some documentation about the fact that the Arg
> > constructor allows inspection that does not respect Eq.
> This follows from Arg's purpose.
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