如何删除这个 ANTLR 语法中的左递归？

发布于 2024-10-27 01:49:44 字数 773 浏览 1 评论 0原文

我正在尝试解析 CSP（通信顺序进程）CSP 参考手册。我定义了以下语法规则。

assignment
    : IDENT '=' processExpression
    ;
processExpression
    :   ( STOP
        | SKIP
        | chaos
        | prefix
        | prefixWithValue
        | seqComposition
        | interleaving
        | externalChoice

        ....

seqComposition
    :   processExpression ';' processExpression
    ;
interleaving
    :   processExpression '|||' processExpression
    ;
externalChoice
    :   processExpression '[]' processExpression
        ;

现在 ANTLR 报告

seqComposition 
interleaving
externalChoice

是左递归的。有什么方法可以删除这个，或者我应该更好地使用 Bison Flex 来处理这种类型的语法。（这样的规则还有很多）

原文

I am trying to parse CSP(Communicating Sequential Processes) CSP Reference Manual. I have defined following grammar rules.

assignment
    : IDENT '=' processExpression
    ;
processExpression
    :   ( STOP
        | SKIP
        | chaos
        | prefix
        | prefixWithValue
        | seqComposition
        | interleaving
        | externalChoice

        ....

seqComposition
    :   processExpression ';' processExpression
    ;
interleaving
    :   processExpression '|||' processExpression
    ;
externalChoice
    :   processExpression '[]' processExpression
        ;

Now ANTLR reports that

seqComposition 
interleaving
externalChoice

are left recursive . Is there any way to remove this or I should better used Bison Flex for this type of grammar. (There are many such rules)

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云仙小弟 2024-11-03 01:49:44

定义一个processTerm。然后编写如下规则：

assignment
    : IDENT '=' processExpression
    ;
processTerm
    :   ( STOP
        | SKIP
        | chaos
        | prefix
        ...
processExpression
    :   ( processTerm
        | processTerm ';' processExpression
        | processTerm '|||' processExpression
        | processTerm '[]' processExpression

        ....

如果您希望仍然定义诸如 seqComposition 之类的内容，我认为这也可以。但您需要确保在执行规则时，processExpansion 的解析始终会消耗更多文本。

Define a processTerm. Then write rules looking like

assignment
    : IDENT '=' processExpression
    ;
processTerm
    :   ( STOP
        | SKIP
        | chaos
        | prefix
        ...
processExpression
    :   ( processTerm
        | processTerm ';' processExpression
        | processTerm '|||' processExpression
        | processTerm '[]' processExpression

        ....

If you want to have things like seqComposition still defined, I think that would be OK as well. But you need to make sure that the parsing of processExpansion is going to always consume more text as you proceed through your rules.

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