blob: 9c754bd87e677cd8ba132850e070ca2d8f8475f1 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
|
{-# LANGUAGE PolyKinds, DataKinds, TypeFamilies, GADTs, MultiParamTypeClasses,
FunctionalDependencies, FlexibleInstances, UndecidableInstances, ExistentialQuantification #-}
module T6068 where
import Prelude hiding (Maybe, Nothing)
data Maybe :: * -> * where
Nothing :: Maybe a
data family Sing (a :: k)
data instance Sing (a :: Maybe k) where
SNothing :: Sing Nothing
data KProxy (a :: *) = KProxy
data Existential (p :: KProxy k) =
forall (a :: k). Exists (Sing a)
class HasSingleton a (kp :: KProxy k) | a -> kp where
exists :: a -> Existential kp
class Floop a b | a -> b
instance forall a (mp :: KProxy (Maybe ak)). Floop a mp => HasSingleton (Maybe a) mp where
exists Nothing = Exists SNothing
-- instance forall (a ::*) (mp :: KProxy (Maybe ak)). HasSingleton (Maybe ak) (Maybe a) mp where
-- exists Nothing = Exists SNothing
|
