ANTLR 语法在解析类似规则时不会回溯

发布于 2025-01-06 05:08:02 字数 464 浏览 3 评论 0原文

假设我有一个语法，它负责全局变量和 C 的某些变体的一些方法声明，

program: (declaration)* (procedure)*;
declaration: typespec identifier ';';
procedure: typespec identifier '(' ')' ';';
typespec: 'char' | 'int';
identifier: ('a' .. 'z' | 'A' .. 'Z') ('A' - 'Z' | 'a' .. 'z' | '0' .. '9' | '_')*;

如果我向它提供类似以下内容：

int MAX;
char proc();

语法读取 int MAX;正确，但随后它想要将声明规则也应用到第二行，并且当它到达 ( 时失败，此时我希望它回溯并应用下一个规则，即程序规则。有人可以告诉我吗为什么这没有发生？

原文

Suppose I have a grammar which takes care of the global variables and some method declarations of some variation of C

program: (declaration)* (procedure)*;
declaration: typespec identifier ';';
procedure: typespec identifier '(' ')' ';';
typespec: 'char' | 'int';
identifier: ('a' .. 'z' | 'A' .. 'Z') ('A' - 'Z' | 'a' .. 'z' | '0' .. '9' | '_')*;

If I feed it something like:

int MAX;
char proc();

the grammar reads int MAX; correctly but then it wants to apply the declaration rule also to the 2nd row, and it fails when it reaches (, and at this point I expect it to backtrack and apply the next rule which is the one for procedure. Could somebody please tell me why this isn't happening?

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深居我梦 2025-01-13 05:08:02

你把你的语法都贴出来了吗？我无法按照您发布的方式编译它...但我尝试了您发布的内容以使其与您的示例相匹配：

program: (declaration)* (procedure)*;
statement: TYPE_SPEC IDENT ;
declaration: statement ';';
procedure: statement '(' ')' ';';

TYPE_SPEC 
    :   'char' | 'int';

IDENT 
    :   ('a' .. 'z' | 'A' .. 'Z') ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' | '_')*;

WHITESPACE
    :   ('\r' | '\n' | '\r\n' | ' ' | '\t' ) {$channel=HIDDEN;} 
    ;

我建议您为标记匹配制定词法分析器规则（大写字母），而不是使它们成为您的解析器规则的一部分 - 如您所见，我已经为您完成了其中一些规则。

Did you post all of your grammar? I couldn't get it to compile as you posted...but I played around with what you posted to make it match your example:

program: (declaration)* (procedure)*;
statement: TYPE_SPEC IDENT ;
declaration: statement ';';
procedure: statement '(' ')' ';';

TYPE_SPEC 
    :   'char' | 'int';

IDENT 
    :   ('a' .. 'z' | 'A' .. 'Z') ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' | '_')*;

WHITESPACE
    :   ('\r' | '\n' | '\r\n' | ' ' | '\t' ) {$channel=HIDDEN;} 
    ;

I'd recommend that your make lexer rules (The ones in capitals) for your token matching rather than making them part of your parser rules - I've done some of them already for you as you can see.

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