NamedDefaults and relaxed defaults?

[Simon Peyton Jones]

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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