data Foo = Foo

class ToMaybeFoo a where
  toMaybeFoo :: a -> Maybe Foo
  
instance ToMaybeFoo Foo where
  toMaybeFoo a = Just a
  
instance ToMaybeFoo (Maybe Foo) where
  toMaybeFoo a = a

myModifiedFn :: ToMaybeFoo a => a -> ()
myModifiedFn a = case toMaybeFoo a of
  Just a -> ()
  Nothing -> ()

main :: IO ()
main = pure $ myModifiedFn Foo

main' :: IO ()
main' = pure $ myModifiedFn (Just Foo)