Explicit type signature for type classes fails

GHC 8.0.1: Consider the indexed classes:

class IxFunctor f where
  imap :: (a -> b) -> f j k a -> f j k b

class IxFunctor m => IxPointed m where
  ireturn :: a -> m i i a

class IxPointed m => IxApplicative m where
  iap :: m i j (a -> b) -> m j k a -> m i k b

class IxFunctor w => IxCopointed w where
  iextract :: w i i a -> a

class IxApplicative m => IxMonad m where
  ibind :: (a -> m j k b) -> m i j a -> m i k b

class IxMonad m => IxMonadFree f m | m -> f where
  iwrap :: f i j (m j k a) -> m i k a

GHCi gives their kinds:

IxFunctor     :: (k -> i -> * -> *)                       -> Constraint
IxPointed     :: (k -> k -> * -> *)                       -> Constraint
IxApplicative :: (k -> k -> * -> *)                       -> Constraint
IxCopointed   :: (k -> k -> * -> *)                       -> Constraint
IxMonad       :: (k -> k -> * -> *)                       -> Constraint
IxMonadFree   :: (k -> k -> * -> *) -> (k -> k -> * -> *) -> Constraint

so I attempt to make them explicit:

type IxFunct i = i -> i -> Type -> Type

class IxFunctor (f :: IxFunct i) where
  imap :: (a -> b) -> f j k a -> f j k b                                                               

Works fine, but if I add it to any of the others it fails:

-- tZRa.hs:15:17: error: … 
--     • Expected kind ‘i’, but ‘i’ has kind ‘*’
--     • In the first argument of ‘w’, namely ‘i’
--       In the type signature:
--         iextract :: w i i a -> a
--       In the class declaration for ‘IxCopointed’
-- Compilation failed.
class IxFunctor w => IxCopointed (w :: IxFunct i) where
  iextract :: w i i a -> a

-- ...
class IxMonad m => IxMonadFree (f :: IxFunct i) (m :: IxFunct i) | m -> f where
  iwrap :: f i j (m j k a) -> m i k a

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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