ref: 32a97fd5217ed6b2b312f6b634ca316f8dc7e0fe
dir: /tests/PolyKind.hs/
module PolyKind(main) where
import Prelude
type Proxy :: forall (k::Kind) . k -> Type
data Proxy a = Proxy
data TypeRep = TypeRep String [TypeRep]
mkAppTy :: TypeRep -> TypeRep -> TypeRep
mkAppTy (TypeRep tc trs) tr = TypeRep tc (trs ++ [tr])
instance Show TypeRep where
show (TypeRep s []) = s
show (TypeRep s ts) = "(" ++ unwords (s : map show ts) ++ ")"
type Typeable :: forall (k::Kind) . k -> Constraint
class Typeable a where
typeRep :: forall proxy . proxy a -> TypeRep
typeOf :: forall a . Typeable a => a -> TypeRep
typeOf _ = typeRep (Proxy :: Proxy a)
instance Typeable Int where
typeRep _ = TypeRep "Int" []
instance Typeable IO where
typeRep _ = TypeRep "IO" []
instance forall f a . (Typeable f, Typeable a) => Typeable (f a) where
typeRep _ = mkAppTy (typeRep (Proxy :: Proxy f)) (typeRep (Proxy :: Proxy a))
main :: IO ()
main = do
print $ typeRep (Proxy :: Proxy Int)
print $ typeRep (Proxy :: Proxy IO)
print $ typeRep (Proxy :: Proxy (IO Int))