As per section 155(1) of Indian evidence act ,that any person can be called to impeach credit of witness and to declare him unworthy. And when we read explanation of section 155 they say that in examination in chief he is not bound to state reasons to belive another person unworthy. So my question is the person which we are calling to declare another witness unworthy that person can be called to during cross examination stage or we have to wait until our turn will come for evidences ?