Unbound kind variable can appear in RHS of associated type
Consider the following code:
{-# LANGUAGE TypeFamilies, PolyKinds, MultiParamTypeClasses,
FlexibleInstances, DataKinds #-}
data KProxy (a :: *) = KP
class Foo (a :: k1) (b :: k2) where
type Bar a
instance Foo (a :: k1) (b :: k2) where
type Bar a = (KP :: KProxy k2)
The kind variable k2
appears on the RHS of the instance for Bar
but not on the left-hand side. This is disallowed for type variables, but there seems to be no check for kind variables.
I will fix in an upcoming patch.
Trac metadata
Trac field | Value |
---|---|
Version | 7.6.3 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |