ambiguous record field (but not *that* kind of ambiguous record field)

[Sebastian Graf]

Hi Richard,

I'm not sure if I'm missing something, but my adolescent naivety in 
frontend matters would try to reach for
https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0155-type-lambda.rst#motivation 
and write

   MkRec { field = \@a -> ... }

and I hope that will do the right thing. Indeed, I interpret your 
proposed `field @a = ...` as much the same.

Sebastian


------ Originalnachricht ------
Von: "Richard Eisenberg" <lists at richarde.dev>
An: "Erdi, Gergo via ghc-devs" <ghc-devs at haskell.org>
Gesendet: 16.05.2022 21:09:33
Betreff: ambiguous record field (but not *that* kind of ambiguous record 
field)

>Hi all,
>
>On a project I'm working on, I wish to declare something like
>
>data Rec = MkRec { field :: forall a. SomeConstraint a => ... }
>
>where the ... contains no mention of `a`.
>
>Even with https://github.com/ghc-proposals/ghc-proposals/pull/448, I 
>think there is no way to avoid the ambiguity when setting `field`. Is 
>that correct? If so, what shall we do about it? The natural answer is 
>somehow to write ... MkRec { field @a = ... } ... but that would break 
>significant new syntactic ground. (Maybe it's good new syntactic 
>ground, but it would still be very new.)
>
>Thanks,
>Richard
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