Question on typeclasses: Can we make all instances of Enum and Bool instances of Generator?

typeclass_question.hs

class Generator a where
  generate :: [a]

data Media = Book | Video deriving (Enum, Bounded, Show)
data Category = Fiction | NonFiction deriving (Enum, Bounded, Show)
data Item = Item Media Category deriving (Show)

instance Generator Media where
  generate = [minBound..maxBound]

instance Generator Category where
  generate = [minBound..maxBound]   -- yuck, repetition!

instance Generator Bool where
  generate = [minBound..maxBound]   -- same 

-- ....
-- QUESTION: Can we make all instances of Enum and Bool instances of Generator?
-- 
-- instance (Enum a, Bounded a) => Generator a where
-- generate = [minBound..maxBound]

-- Note that not all instances of our Generator typeclass are instances
-- of Enum and Bounded, and need a different implementation. E.g. this one:
instance Generator Item where
  generate = [Item m c | m<-generate, c<-generate]

main = do
  print (generate :: [Item])
  print (generate :: [Bool])

-- alternative: don't use a typeclass.  Ok, but we'd like to refer to 
-- all instances of generator sometimes.
gen2 :: (Enum a, Bounded a) => [a]
gen2 = [minBound..maxBound]
main2 = print $ (gen2::[Bool])