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{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeInType #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableInstances #-}
module T14174a where
import Data.Kind
data TyFun :: * -> * -> *
type a ~> b = TyFun a b -> *
infixr 0 ~>
type family Apply (f :: k1 ~> k2) (x :: k1) :: k2
type a @@ b = Apply a b
infixl 9 @@
data FunArrow = (:->) | (:~>)
class FunType (arr :: FunArrow) where
type Fun (k1 :: Type) arr (k2 :: Type) :: Type
class FunType arr => AppType (arr :: FunArrow) where
type App k1 arr k2 (f :: Fun k1 arr k2) (x :: k1) :: k2
type FunApp arr = (FunType arr, AppType arr)
instance FunType (:->) where
type Fun k1 (:->) k2 = k1 -> k2
instance AppType (:->) where
type App k1 (:->) k2 (f :: k1 -> k2) x = f x
instance FunType (:~>) where
type Fun k1 (:~>) k2 = k1 ~> k2
instance AppType (:~>) where
type App k1 (:~>) k2 (f :: k1 ~> k2) x = f @@ x
infixr 0 -?>
type (-?>) (k1 :: Type) (k2 :: Type) (arr :: FunArrow) = Fun k1 arr k2
type family ElimBool (p :: Bool -> Type)
(z :: Bool)
(pFalse :: p False)
(pTrue :: p True)
:: p z where
-- Commenting out the line below makes the panic go away
ElimBool p z pFalse pTrue = ElimBoolPoly (:->) p z pFalse pTrue
type family ElimBoolPoly (arr :: FunArrow)
(p :: (Bool -?> Type) arr)
(z :: Bool)
(pFalse :: App Bool arr Type p False)
(pTrue :: App Bool arr Type p True)
:: App Bool arr Type p z
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