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{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeInType #-}
{-# LANGUAGE TypeApplications #-}
module T15346 where
import Data.Kind
import Data.Proxy
-----
type family Rep (a :: Type) :: Type
type instance Rep () = ()
type family PFrom (x :: a) :: Rep a
-----
class SDecide k where
test :: forall (a :: k). Proxy a
instance SDecide () where
test = undefined
test1 :: forall (a :: k). SDecide (Rep k) => Proxy a
test1 = seq (test @_ @(PFrom a)) Proxy
test2 :: forall (a :: ()). Proxy a
test2 = test1
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