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 |