Kind inference does not propagate annotations on associated types
Consider the following:
{-# LANGUAGE KindSignatures, TypeFamilies, PolyKinds #-}
data Proxy a = Proxy
class C a where
type F (a :: *) :: *
op :: Proxy a -> Int
instance C [] where
op _ = 5When compiled, this code generates a warning saying that F [] is undefined. That's a good warning, but the problem is that the code is erroneous and should not compile. The problem is that the kind annotation on a in the declaration of the family F says that a should have kind *. However, I am permitted to write an instance for [], which does not have kind *.
After playing around with this, I was unable to find a way to cause a type safety error, but the behavior should probably be fixed.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.7 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |