cannot derive new-typeable instances for promoted data types taking parameters
Hi,
The following code shows the issue:
{-# LANGUAGE DataKinds, DeriveDataTypeable, KindSignatures, PolyKinds, StandaloneDeriving #-}
import Data.Typeable
import GHC.TypeLits
data T (a :: [*]) = T deriving (Typeable)
t = T :: T [Int, Double]
deriving instance Typeable '[]
{-
*Main> typeOf t
<interactive>:24:1:
No instance for (Typeable (* -> [*] -> [*]) ((':) *))
arising from a use of ‛typeOf’
In the expression: typeOf t
In an equation for ‛it’: it = typeOf t
-}
ghc7.7-20131004 doesn't allow either of the following:
deriving instance (Typeable a, Typeable b) => Typeable (a ': b)
-- or
deriving instance Typeable (':)
On ghc-7.6 I could write my own instance Typeable (T a)
, but this has been disabled it seems.
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 |