# Pastebin f5DVk1QJ
{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}

import Data.Proxy

data Alice

class C x where
  silly :: String

instance C Alice where
  silly = "Silly Alice"

data Foo a where
  Foo :: C a => Foo a

f :: forall a . Foo a -> String
f Foo = silly @a