NamedDefaults and relaxed defaults?

[Benjamin Redelings]

Thanks!

It looks like ExtendedDefaultRules already allows default variables that 
co-occur with multiparameter constraints and non-standard classes.  So 
maybe that solves my issue with (Num a, Convertible a Double).

Does the defaulting for RuntimeRep interact with class defaulting?

-BenRI

On 7/26/23 12:11 PM, Simon Peyton Jones wrote:
> No: I don't know of anyone planning to implement this proposal -- 
> indeed I had forgotten about it -- so it's waiting for someone to take 
> it on.
>
> There are some slightly tricky loose ends around defaulting that it'd 
> be good to nail down first: 
> https://gitlab.haskell.org/ghc/ghc/-/issues/20686
>
> Simon
>
> On Wed, 26 Jul 2023 at 11:00, Benjamin Redelings 
> <benjamin.redelings at gmail.com> wrote:
>
>     Hi,
>
>     If I understand correctly, the traditional defaulting rules prevent
>     defaulting variables with constraints like (Num a, Convertible a
>     Double), but the NamedDefaults proposal would allow defaulting a ~
>     Double in this case due to the relaxed defaulting rules in section
>     2.5
>     of the proposal:
>
>     https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0409-exportable-named-default.rst#id2
>
>     1. Is there any plan to start implementing NamedDefaults?  I saw the
>     comment from Simon P-J that it would not be fun to implement
>     because it
>     might require orphan default declarations... so perhaps there's no
>     plan
>     to implement this?
>
>     2. Would it be worth adding a separate LANGUAGE option that just
>     implements the relaxed defaulting rules in section 2.5?
>     Specifically (a)
>     allowing variables with multiparameter constraints and (b) allowing
>     variables with constraints that are not in the Prelude.
>
>     3. Am I correct in assuming that the relaxed defaulting rules require
>     NamedDefaults to be enabled in the importing module, and not just
>     in the
>     imported model?
>
>     -BenRI
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