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+{-# LANGUAGE QuantifiedConstraints #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE DeriveFunctor #-}
+
+-- The instances below have large demands, though I think they're pretty sane.
+{-# LANGUAGE UndecidableInstances #-}
+
+-- This test uses recursive dictionaries
+-- where we do addSolvedDict before solving sub-goals
+
+module Main where
+
+data Foo f a = Foo (f (Maybe a))
+deriving instance Show (f (Maybe a)) => Show (Foo f a)
+deriving instance Functor f => Functor (Foo f)
+
+data Bar x a = Pure a | Bar (x (Bar x) a)
+-- This Show instance is knarly. Basically we ask @x f@ to preserve Show whenever @f@ preserves Show.
+deriving instance (forall f b. (Show b, forall c. Show c => Show (f c))
+                            => Show (x f b), Show a)
+               => Show (Bar x a)
+deriving instance (forall f. Functor f => Functor (x f))
+               => Functor (Bar x)
+
+-- I should now be able to get Show and Functor for @Bar Foo@.
+-- This will involve mutual recursion between the Show/Functor instances for Foo and Bar.
+main :: IO ()
+main = print $ fmap (<> " there") $ Bar $ Foo $ Pure $ Just "Hello"