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+{-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE ImportQualifiedPost #-}
+
+-- Exercise 13.2-ii
+-- Use `GHC.Generics` to implement the function `exNihilo :: Maybe a`.
+
+import GHC.Generics qualified as G
+
+class GExNihilo a where
+  gexNihilo :: Maybe (a x)
+
+instance GExNihilo G.U1 where
+  gexNihilo = Just G.U1
+
+instance GExNihilo G.V1 where
+  gexNihilo = Nothing
+
+instance GExNihilo (G.K1 _1 a) where
+  gexNihilo = Nothing
+
+instance GExNihilo (a G.:+: b) where
+  gexNihilo = Nothing
+
+instance GExNihilo (a G.:*: b) where
+  gexNihilo = Nothing
+
+instance GExNihilo a => GExNihilo (G.M1 _x _y a) where
+  gexNihilo = G.M1 <$> gexNihilo
+
+-- I could not figure this one out so had to look at the solution. I noticed
+-- Sandy missed to provide the actual implementation of `exNihilo` so here is
+-- my version:
+exNihilo :: forall a. (G.Generic a, GExNihilo (G.Rep a)) => Maybe a
+exNihilo = G.to <$> gexNihilo @(G.Rep a)
+
+-- Example usage:
+data MyUnit = MyUnit deriving (G.Generic, Show)
+
+newtype MyType a = MyType a deriving (G.Generic, Show)
+
+data MySum = MySum1 | MySum2 deriving (G.Generic, Show)
+
+t1 = exNihilo @MyUnit -- Just MyUnit
+
+t2 = exNihilo @(MyType ()) -- Nothing
+
+t3 = exNihilo @MySum -- Nothing