# Pastebin 2JZN7jmT
{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}

import Data.Proxy
import Data.Constraint

data Alice

class C x where
  silly :: String

instance C Alice where
  silly = "Silly Alice"

data Foo where
  Foo :: Dict (C a) -> Foo

f :: Foo -> String
f (Foo (dict :: Dict (C a))) = withDict dict $ silly @a