是否有可能重新实现使用GHC泛型得出的"Enum"

是否有可能Enum使用GHC泛型重新实现类型类的派生？

起初,它看起来很简单:

data Foo -- representation without metadata (wrong):
  = Foo  -- L1 U1
  | Bar  -- R1 (L1 U1)
  | Baz  -- R1 (R1 (L1 U1))
  | Quux -- R1 (R1 (R1 U1))
  deriving (Show, Eq, Generic)

-- Rep Foo p = (U1 :+: (U1 :+: (U1 :+: U1))) p

instance Enum Foo where
  toEnum   = undefined -- FIXME
  fromEnum = gfromEnum . from

class GEnum f where
  gfromEnum :: f p -> Int

instance GEnum U1 where
  gfromEnum U1 = 0

instance GEnum f => GEnum (M1 i t f) where
  gfromEnum (M1 x) = gfromEnum x

instance (GEnum x, GEnum y) => GEnum (x :+: y) where
  gfromEnum (L1 x) = gfromEnum x
  gfromEnum (R1 y) = 1 + gfromEnum y

?> fromEnum Foo
0
?> fromEnum Bar
1
?> fromEnum Baz
1
?> fromEnum Quux
2

((U1 :+: U1) :+: (U1 :+: U1)) p