ANTLR如何使用具有相同开始的词法分析器规则? [英] ANTLR How to use lexer rules having same starting?

问题描述

如何使用开头相同的词法分析器规则?

How to use lexer rules having same starting?

我正在尝试使用两个相似的词法分析器规则(具有相同的开头):

I am trying to use two similar lexer rules (having the same starting):

TIMECONSTANT: ('0'..'9')+ ':' ('0'..'9')+;
INTEGER     : ('0'..'9')+;
COLON       : ':';

这是我的示例语法:

grammar TestTime;

text      : (timeexpr | caseblock)*;

timeexpr  : TIME;
caseblock : INT COLON ID;

TIME      : ('0'..'9')+ ':' ('0'..'9')+;
INT       : ('0'..'9')+;
COLON     : ':';
ID        : ('a'..'z')+;

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

当我尝试解析文本时:

12:44
123 : abc
123: abc

正确解析了前两行，第3行-产生错误. 由于某些原因，"123:" ANTLR解析为TIME(而并非如此)...

First two lines are parsed correctly, 3rd - generates error. For some reason, '123:' ANTLR parses as TIME (while it is not)...

那么，有可能用这样的词法来做语法吗?

So, is it possible to make grammar with such lexems?

在我的语言中，必须具有这样的规则才能同时使用大小写块和日期时间常量.例如，用我的语言可以写:

Having such rules is necessary in my language for using both case-blocks and datetime constants. For example in my language it is possible to write:

case MyInt of
  1: a := 01.01.2012;
  2: b := 12:44;
  3: ....
end;

推荐答案

一旦匹配了DIGIT+ ':'，词法分析器便期望其后跟随另一个DIGIT来匹配TIMECONSTANT.如果这没有发生，则它不能依赖于另一个匹配DIGIT+ ':'的词法分析器规则，并且该词法分析器不会放弃已经匹配的':'来匹配INTEGER.

As soon DIGIT+ ':' is matched, the lexer expects this to be followed by another DIGIT to match a TIMECONSTANT. If this does not happen, it cannot fall back on another lexer rule that matches DIGIT+ ':' and the lexer will not give up on the already matched ':' to match an INTEGER.

一种可能的解决方案是在INTEGER规则的末尾有选择地匹配':' DIGIT+，并在匹配时更改令牌的类型:

A possible solution would be to optionally match ':' DIGIT+ at the end of the INTEGER rule and change the type of the token if this gets matched:

grammar T;  

parse
 : (t=. {System.out.printf("\%-15s '\%s'\n", tokenNames[$t.type], $t.text);})* EOF
 ;

INTEGER      : DIGIT+ ((':' DIGIT)=> ':' DIGIT+ {$type=TIMECONSTANT;})?;
COLON        : ':';
SPACE        : ' ' {skip();};

fragment DIGIT : '0'..'9';
fragment TIMECONSTANT : ;

解析输入时:

11: 12:13 : 14

将打印以下内容:

INTEGER         '11'
COLON           ':'
TIMECONSTANT    '12:13'
COLON           ':'
INTEGER         '14'

编辑

不太好，但是可以...

Not too nice, but works...

是的.但是，这并不是ANTLR的不足:我知道的大多数词法分析器生成器都会遇到对这样的TIMECONSTANT正确标记的问题(当同时存在INTEGER和COLON时). ANTLR至少有助于在词法分析器中进行处理:)

True. However, this is not an ANTLR short coming: most lexer generators I know will have a problem properly tokenizing such a TIMECONSTANT (when INTEGER and COLON are also present). ANTLR at least facilitates a way to handle it in the lexer :)

您可以也可以让它由解析器而不是词法分析器来处理:

You could also let this be handled by the parser instead of the lexer:

time_const : INTEGER COLON INTEGER;
INTEGER    : '0'..'9'+;
COLON      : ':';
SPACE      : ' ' {skip();};

但是，如果您语言的词法分析器忽略空格，则输入如下内容:

However, if your language's lexer ignores white spaces, then input like:

12 :    34

当然，

也将通过time_const规则匹配.

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