I use the same F1 trick (with the same name and for the same reason) in the
HEAD branch of hkd and distributive, but I admit it is a bit frustrating,
because then I have to expose pattern synonyms to hide its boilerplate from
users.
e.g.
> I figured out that this compiles:
>
> data HKD (f :: Type -> Type) = Foo (F1 Int f) (F1 Double f)
> | Bar (F1 Bool f)
> deriving Generic1
>
> newtype F1 a f = F1 { unF1 :: f a }
Yes, that's a useful trick to keep in mind. For what it's worth, I think
your `F1` is the same thing as `Barbie`
Thanks for posting an example—that's very helpful to figure out what is
going on.
> Currently, GHC rejects the following code:
>
> {-# LANGUAGE DeriveGeneric #-}
> {-# LANGUAGE PolyKinds #-}
> import GHC.Generics
>
> data HKD f = Foo (f Int) (f Double)
> | Bar (f Bool)
> deriving Generic1
Hello,
I'm not quite sure I understand the issue you're hitting. Generic1 is
poly-kinded, so I would expect it to be able to handle data types where the
last type parameter has differing kinds. Can you post a complete example of
the program you expect to typecheck, but doesn't?
Best,
Ryan
I was hacking GHC to see if it's able to derive Generic1 instance for
datatypes with kind (Type -> Type) -> Type by omitting some checks. I
noticed that the type parameter is substituted by GHC.Types.Any, preventing
higher-kinded instances from typechecking. I found a comment implying that
this is
