Derive Generic1 instances for types of kind (k -> *) -> * that include applications of the parameter

The Generic1 class is polykinded. The DeriveGeneric extension can derive Generic1 instances for types of kind k -> * parameterized over a parameter with a kind other than k ~ *, but only if they don't apply the parameter to other types.

It currently cannot derive an instance for

newtype Fix f = In (f (Fix f))
  deriving (Generic1)

or for

data Child f = Child {
    ordinal :: Int,
    nickname :: f String
}
  deriving (Generic1)

It's possible to represent these types generically, either with composition that can include occurrences of the parameter or with new types that represent applications of the parameter.

Trac metadata

Trac field	Value
Version
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	low
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture