[Haskell-cafe] Downsides to disabling unticked-promoted-constructor warning?

[David Feuer]

There can also be ambiguities in type families. For example,

data T = T
type family Fam a where
  Fam Int = T

Do we have Fam :: Type -> Type or Fam :: Type -> T?

On Thu, Oct 21, 2021, 12:15 PM Markus Läll <markus.l2ll at gmail.com> wrote:

> Hi and thank you both!
>
> For disambiguation the tick may be required for syntactically empty and
> one element lists, right? As only these can be ambiguous at locations where
> a type is expected.
>
>
> On Wed, Oct 20, 2021 at 3:29 PM Adam Gundry <adam at well-typed.com> wrote:
>
>> I've created a ticket to request disabling this warning by default:
>> https://gitlab.haskell.org/ghc/ghc/-/issues/20531
>>
>> I'm not sure if this needs a full ghc-proposal.
>>
>> Cheers,
>>
>> Adam
>>
>>
>>
>> On 18/10/2021 03:19, Richard Eisenberg wrote:
>> > As its author, I think -Wunticked-promoted-constructors is a
>> misfeature. It was motivated by the fact that writing [True] when you mean
>> '[True] produces a cascade of obscure kind errors, and so I thought it was
>> good to encourage people to always write the ticks. But the feature does
>> not achieve its goal: because errors squelch warnings, we do not see the
>> warnings if there are any errors. Furthermore, I agree with Adam's post
>> that I've come to prefer a style where we leave off the ticks (where
>> possible).
>> >
>> > Bottom line: feel free to turn this warning off.
>> >
>> > Richard
>> >
>> >> On Oct 16, 2021, at 5:55 AM, Markus Läll <markus.l2ll at gmail.com>
>> wrote:
>> >>
>> >> Hi!
>> >>
>> >> Is there any consensus on unticked promoted constructors -- are they
>> generally safe to use?
>> >>
>> >> Currently the warning is part of -Wall, but having promoted
>> constructors unticked is just aesthetically nicer.
>> >>
>> >>
>> >> Thanks,
>> >>
>> >> --
>> >> Markus Läll
>>
>>
>> --
>> Adam Gundry, Haskell Consultant
>> Well-Typed LLP, https://www.well-typed.com/
>>
>> Registered in England & Wales, OC335890
>> 118 Wymering Mansions, Wymering Road, London W9 2NF, England
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>
>
>
> --
> Markus Läll
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