将EBNF转换为BNF [英] Converting EBNF to BNF

问题描述

距离我的计算机语言课程已有几年了，所以我忘记了BNF和EBNF的优缺点，而且我旁边没有教科书.具体来说，我忘记了如何将EBNF转换为BNF.

It's been a few years since my computer-language class and so I've forgotten the finer points of BNF's and EBNF's and I don't have a textbook next to me. Specifically, I've forgotten how to convert an EBNF into BNF.

据我所知，我知道要点之一就是将{ term }转换为<term> | <many-terms>.但我不记得其他规则.我试图在网上查找此内容，但只能找到指向家庭作业问题的链接，或者有关用花括号转换术语的小注释.我找不到定义翻译的详尽规则列表.

From what little I remember, I know that one of the main points is to convert { term } into <term> | <many-terms>. But I don't remember the other rules. I've tried to look this up online but I can only find links to either homework questions, or a small comment about converting terms with curly braces. I can't find an exhaustive list of rules that define the translation.

推荐答案

请参见以下链接，其中包含有关每个需要转换的作品的说明:

Please see the following link, it contains instructions for each production that needs to be converted:

http://lampwww.epfl. ch/teaching/archive/compilation-ssc/2000/part4/parsing/node3.html

对于构建解析器(尤其是自底向上)，BNF语法通常比EBNF更好.但是将EBNF语法转换为BNF很容易:

For building parsers (especially bottom-up) a BNF grammar is often better, than EBNF. But it's easy to convert an EBNF Grammar to BNF:

• 将每个重复{ E }转换为新的非终止X并添加

• Convert every repetition { E } to a fresh non-terminal X and add

X = ε | X E.

将每个选项[ E ]转换为新的非终端X并添加

Convert every option [ E ] to a fresh non-terminal X and add

X = ε | E.

(我们可以将X = A [ E ] B.转换为X = A E B | A B.)

将每个组( E )转换为新的非终端X并添加

Convert every group ( E ) to a fresh non-terminal X and add

X = E.

我们甚至可以通过使用非终端相同的多个产品来消除替代方案.

We can even do away with alternatives by having several productions with the same non-terminal.

X = E | E'.变为X = E. X = E'.

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