I wrote a translator for this purpose. Universal-transpiler is able to convert ANTLR grammars into PEG.js, nearley, ABNF, XBNF, and several other grammar notations. It is not yet able to translate ANTLR into W3C-BNF, but I will try to add this feature in a future version.
This translator is only compatible with a small subset of the ANTLR language, but I hope it will still be useful.
but you should be able to convert at least the common subset - has anyone done yet automatically?
Not that I know of. And if it does exist, I've never seen this tool being discussed on the ANTLR mailing list that I read on a regular basis.
Also note that many BNF-variants allow for left-recursive rules, something that an LL-parser generator like ANTLR cannot cope with. The left recursive rules can of course be re-factored out by the tool, but that could be rather tricky, and will probably result in a far less "readable" grammar than one would get than doing this manually.
As to converting ANTLR grammars into BNF-like form would be easier I guess, although only with the most trivial grammars. As soon as various types of predicates are put into an ANTLR grammar, the conversion might again become tricky.
Antlr4 does allow left recursion, with remarkable flexibility. I found a modern tool to convert to and from Antlr grammars to other types of grammars. This is well supported at this time: trconvert
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我为此目的写了一个翻译器。 Universal-transpiler 能够转换 ANTLR 语法进入 PEG.js, 近，ABNF，XBNF 以及其他一些语法符号。目前还无法将 ANTLR 转换为 W3C-BNF，但我会尝试在未来版本中添加此功能。
该翻译器仅与 ANTLR 语言的一小部分兼容，但我希望它仍然有用。
I wrote a translator for this purpose. Universal-transpiler is able to convert ANTLR grammars into PEG.js, nearley, ABNF, XBNF, and several other grammar notations. It is not yet able to translate ANTLR into W3C-BNF, but I will try to add this feature in a future version.
This translator is only compatible with a small subset of the ANTLR language, but I hope it will still be useful.
ANTLR (v3) 是用以下语法“用自己的话”编写的（正如特伦斯·帕尔本人所说）：
http://www.antlr.org/grammar/ANTLR/ANTLRv3.g
据我所知没有。如果它确实存在，我也从未在我定期阅读的 ANTLR 邮件列表上看到过讨论这个工具。
另请注意，许多 BNF 变体允许 左递归 规则，这是 LL 解析器生成器像ANTLR无法应对。左递归规则当然可以由该工具重新分解，但这可能相当棘手，并且可能会导致比手动执行此操作所得到的语法“可读”得多。
至于将 ANTLR 语法转换为类似 BNF 的形式，我想会更容易，尽管只是使用最简单的语法。一旦将各种类型的谓词放入 ANTLR 语法中，转换可能会再次变得棘手。
ANTLR (v3) is written "in its own words" (as Terence Parr himself put it) in this grammar:
http://www.antlr.org/grammar/ANTLR/ANTLRv3.g
Not that I know of. And if it does exist, I've never seen this tool being discussed on the ANTLR mailing list that I read on a regular basis.
Also note that many BNF-variants allow for left-recursive rules, something that an LL-parser generator like ANTLR cannot cope with. The left recursive rules can of course be re-factored out by the tool, but that could be rather tricky, and will probably result in a far less "readable" grammar than one would get than doing this manually.
As to converting ANTLR grammars into BNF-like form would be easier I guess, although only with the most trivial grammars. As soon as various types of predicates are put into an ANTLR grammar, the conversion might again become tricky.
有一个网站提供了大量的语法和工具来在其格式之间进行转换：
http:// slebok.github.io/zoo/index.html
There's a site that host a huge variety of grammars and tools to convert between their formats:
http://slebok.github.io/zoo/index.html
Antlr4 确实允许左递归，具有显着的灵活性。我找到了一个现代工具，可以在 Antlr 语法与其他类型的语法之间进行转换。目前这得到了很好的支持：
trconvert
Antlr4 does allow left recursion, with remarkable flexibility. I found a modern tool to convert to and from Antlr grammars to other types of grammars. This is well supported at this time:
trconvert