polykinds error: Found `k' but expected `k'
{-# OPTIONS -XTypeFamilies -XDataKinds -XPolyKinds #-}
class Foo (xs :: [k]) where
type Bar xs :: *
instance Foo '[] where
type Bar '[] = Int
fails with:
I:\a.hs:7:5:
Type indexes must match class instance head
Found `k' but expected `k'
In the type instance declaration for `Bar'
In the instance declaration for `Foo '[]'
If I change the kind of xs from [k] to [*], the program is accepted.
Trac metadata
Trac field | Value |
---|---|
Version | 7.6.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |