def add_callback(self, ar, *msgs):
        if len(msgs) > 1:
            msg = '\n'.join([force_text(s) for s in msgs])
        else:
            msg = msgs[0]

        return Callback(ar, msg)
Returns an "action callback" which will initiate a dialog thread
dataset/ETHPy150Open lsaffre/lino/lino/core/kernel.py/Kernel.add_callback