删除左递归 [英] Removing left recursion

问题描述

以下语法已退出递交

E= E+T|T
T= T*F|F
F= a|b|c

有没有一般的程序？

推荐答案

是的，有一个一般的程序， 维基百科。

Yes, there is a general procedure, see e.g. wikipedia.

E = TE'
E'= (e) | +TE'
T = FT'
T'= (e) | *FT'
F = a | b | c

应该提到这会改变 + 和 * 从左到右。也就是说， a + b + c 之前分析为（a + b）+ c 解析为 a +（b + c）。

It should be mentioned that this alters the associativity of + and * from left to right. That is, where before a + b + c was parsed as (a + b) + c, it is now parsed as a + (b + c).

这不是加法和乘法的问题，

This is not a problem for addition and multiplication, but it would be a problem for subtraction and division, for example.

维基百科文章有更详细的左递归移除程序及其复杂性。

Wikipedia article has more detail on the left-recursion removal procedure and its intricacies.

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