Create a reader for singleton declaration and it's members

They must complain about members' declarations with or without implementation.
example:

```scala

singleton None extends Monad[_]: // by context, where `?` means type validated in compilation type, By default Any.
	map(u => ?V): Self = self
	flatMap(_ => Monad[?V]) = self

	_apply(u: ?U): Monad[U] = MonadImpl(u)

```