code: func (r *Program) SetUID(uid string) error {
  	if r.owner != nil {
  		id, exists := r.owner.seenProgs[uid]
  		if exists {
  			if id != r.id {
  				return errors.New("sam: uid exists")
  			}
  			return nil
  		}
  		delete(r.owner.seenProgs, r.uid)
  		r.owner.seenProgs[uid] = r.id
  	}
  	r.uid = uid
  	return nil
  }
docs: // SetUID sets the unique program ID to uid.