MINIMAL XOR (Was: Proposal: Make Eq type class single method)

[David Feuer]

I think the only time they're not potentially contradictory is when you're
dealing with singletons, and that's a pretty special case.

On Wed, Oct 27, 2021, 11:15 AM Carter Schonwald <carter.schonwald at gmail.com>
wrote:

> not necessarily ... there could be  contradictory sets of methods! :)
>
> like the minimal sets for Field type class,  the xor would be for defining
> '/' in terms of reciprocal and times or vice versa (/ vs recip) and
> likewise (negate vs minus) etc etc
>
> On Wed, Oct 27, 2021 at 6:38 AM Henning Thielemann <
> lemming at henning-thielemann.de> wrote:
>
>>
>> On Mon, 25 Oct 2021, Carter Schonwald wrote:
>>
>> > i agree with Tom and Hecate,more strongly:
>> >
>> https://github.com/ghc/ghc/blob/98aa29d3fe447cce3407e6864b015892244bb475/libraries/ghc-prim/GHC/Classes.hs#L142-L150
>>
>> > the current definition DOES NOT require defining both.
>> >
>> > as it currently stands, you only need to define one of '==' XOR  '/='
>> >
>> > this actually suggests an interesting and DIFFERENT
>> ecosystem improvement, (ignoring IEEE non-signalling NANs),
>> > namely we add support for XOR to minimal pragma syntax and issue a
>> warning
>> >
>> > perhaps something like adding (XOR "reason String" clauseExpr1
>> clauseexpr2) ?
>>
>> The problem of implementing two methods in a contradictory way arises for
>> any OR in MINIMAL pragma, right?
>
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