将 EBNF 转换为 BNF

发布于 2024-08-25 08:55:13 字数 287 浏览 7 评论 0原文

我的计算机语言课已经过去几年了，所以我已经忘记了 BNF 和 EBNF 的要点，而且我身边也没有教科书。具体来说，我忘记了如何将 EBNF 转换为 BNF。

据我所知，我知道要点之一是转换

{ term }

为

<term> | <many-terms>

但我不记得其他规则。我尝试在网上查找此内容，但只能找到家庭作业问题的链接，或有关用大括号转换术语的小评论。我找不到定义翻译的详尽规则列表。

原文

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.

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.

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滴情不沾 2024-09-01 08:55:13

请参阅此页面。

See this page.^???? It contains instructions for each production that needs to be converted:

From EBNF to BNF
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:
Convert every repetition { E } to a fresh non-terminal X and add
X = ε | X E.
Convert every option [ E ] to a fresh non-terminal X and add
X = ε | E.
(We can convert X = A [ E ] B. to X = A E B | A B.)
Convert every group ( E ) to a fresh non-terminal X and add
X = E.
We can even do away with alternatives by having several productions with the same non-terminal.
X = E | E'. becomes X = E. X = E'.