实现了自顶向下深度优先，自顶向下广度优先，自底向上深度优先，自底向上广度优先四个语言分析函数。有助于理解形式语言与计算理论的基本概念。-Depth-first top-down, top-down breadth-first, bottom-up depth-first, bottom-up breadth priority the four linguistic analysis function. Helps to understand the basic concepts of the t