How to use the vine.Thenable function in vine

def call_soon(self, callback, *args):
        if not isinstance(callback, Thenable):
            callback = promise(callback, args)
        self._ready.add(callback)
        return callback

    @property
    def children(self):
        return self.results

    @classmethod
    def restore(cls, id, backend=None, app=None):
        """Restore previously saved group result."""
        app = app or (
            cls.app if not isinstance(cls.app, property) else current_app
        )
        backend = backend or app.backend
        return backend.restore_group(id)


@Thenable.register
@python_2_unicode_compatible
class EagerResult(AsyncResult):
    """Result that we know has already been executed."""

    def __init__(self, id, ret_value, state, traceback=None):
        # pylint: disable=super-init-not-called
        # XXX should really not be inheriting from AsyncResult
        self.id = id
        self._result = ret_value
        self._state = state
        self._traceback = traceback
        self.on_ready = promise()
        self.on_ready(self)

    def then(self, callback, on_error=None, weak=False):
        return self.on_ready.then(callback, on_error)