у кого-нибудь есть GHC не 8.10.2 под рукой? Вот этот код выдает ошибку:
type family Foo k (a :: k) :: * where
Foo * a = a
?
* Expected a type, but `a' has kind `k'
* In the type `a'
In the type family declaration for `Foo'
NB: Type `Foo' was inferred to use visible dependent quantification.
Most types with visible dependent quantification are
polymorphically recursive and need a standalone kind
signature. Perhaps supply one, with StandaloneKindSignatures.