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

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 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 wrote:

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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

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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

On 18/10/2021 03:19, Richard Eisenberg wrote: that I've come to prefer a style where we leave off the ticks (where possible).

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Bottom line: feel free to turn this warning off.

Richard

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On Oct 16, 2021, at 5:55 AM, Markus Läll

wrote:

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Hi!

Is there any consensus on unticked promoted constructors -- are they

generally safe to use?

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Currently the warning is part of -Wall, but having promoted

constructors unticked is just aesthetically nicer.

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Thanks,

-- Markus Läll

-- Adam Gundry, Haskell Consultant Well-Typed LLP, https://www.well-typed.com/

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-- Markus Läll _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.