def add(self, log_prob, next_word_prob):
        """increments counters for the sum of log probs of current word and next
        word (given context ending at current word). Since the next word might be at the end of the example,
        or it might be not counted because it is not an ending subword unit,
        also keeps track of how many of those we have seen"""
        if next_word_prob is not None:
            self.next_word_prob += next_word_prob
        else:
            self.missing_next_words += 1
        self.log_prob += log_prob
        self.count += 1
increments counters for the sum of log probs of current word and next
        word (given context ending at current word). Since the next word might be at the end of the example,
        or it might be not counted because it is not an ending subword unit,
        also keeps track of how many of those we have seen
understand_icl/fairseq/fairseq_cli/eval_lm.py