# 3A.3.1 自顶向下（Top-Down）

从解析树根节点开始，逐步向叶子节点构建整颗解析树的过程叫着自顶向下解析。自顶向下解析就是还原一个最左推导的过程。

本节我们先介绍递归下降算法，再介绍一种受限的自顶向下的解析算法 - 基于LL（1）文法的预测/匹配解析器。


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