-- | Invalid Iso, exists for ease of composition with the current 'Lens . Iso'
-- chaining to hide internal types from the user.
_Default :: Monoid a => Iso' (Maybe a) a
_Default = iso f Just
  where
    f (Just x) = x
    f Nothing  = mempty
_Default :: Monoid a => Iso' (Maybe a) a
_Default = iso f Just
  where
    f (Just x) = x
    f Nothing  = mempty
_Default = iso f Just
  where
    f (Just x) = x
    f Nothing  = mempty