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I'm not sure if this is a bug. File:

{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TypeInType #-}
module T15474 where

import Data.Kind (Type)

data Proxy a

type Forall = forall t. Proxy t

f1 :: forall (t :: Type). Proxy t
f1 = f1

f2 :: Forall
f2 = f1

gives an error message mentioning Any:

    • Couldn't match type ‘GHC.Types.Any’ with ‘*’
      Expected type: Proxy t
        Actual type: Proxy t0

The appearance of Any is suspicious to me - I thought it's an implementation detail?