否定词法分析器规则和内部规则 [英] Negating inside lexer- and parser rules

问题描述

否定元字符~如何在ANTLR的词法分析器规则中使用?

How can the negation meta-character, ~, be used in ANTLR's lexer- and parser rules?

推荐答案

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Negating can occur inside lexer and parser rules.

在lexer规则内部，您可以否定字符，而在解析器规则中，您可以否定标记(lexer规则).但是词法分析器和解析器规则只能分别否定单个字符或单个标记.

Inside lexer rules you can negate characters, and inside parser rules you can negate tokens (lexer rules). But both lexer- and parser rules can only negate either single characters, or single tokens, respectively.

几个例子:

要匹配一个或多个字符(小写的ascii字母除外)，您可以执行以下操作:

To match one or more characters except lowercase ascii letters, you can do:

NO_LOWERCASE : ~('a'..'z')+ ;

(否定元字符~的优先级高于+，因此上述规则等于(~('a'..'z'))+)

(the negation-meta-char, ~, has a higher precedence than the +, so the rule above equals (~('a'..'z'))+)

请注意，'a'..'z'与单个字符匹配(因此可以取反)，但是以下规则无效:

Note that 'a'..'z' matches a single character (and can therefor be negated), but the following rule is invalid:

ANY_EXCEPT_AB : ~('ab') ;

因为'ab'(显然)匹配2个字符，所以不能取反.要匹配包含2个字符但不包含'ab'的令牌，您必须执行以下操作:

Because 'ab' (obviously) matches 2 characters, it cannot be negated. To match a token that consists of 2 character, but not 'ab', you'd have to do the following:

ANY_EXCEPT_AB 
  :  'a' ~'b' // any two chars starting with 'a' followed by any other than 'b'
  |  ~'a' .   // other than 'a' followed by any char
  ;

解析器规则

在解析器规则中，~取反某个令牌或多个令牌.例如，您定义了以下标记:

parser rules

Inside parser rules, ~ negates a certain token, or more than one token. For example, you have the following tokens defined:

A : 'A';
B : 'B';
C : 'C';
D : 'D';
E : 'E';

如果您现在想匹配除A以外的任何令牌，请执行以下操作:

If you now want to match any token except the A, you do:

p : ~A ;

如果要匹配除B和D之外的任何令牌，则可以执行以下操作:

And if you want to match any token except B and D, you can do:

p : ~(B | D) ;

但是，如果您要匹配除A后跟B的任意两个令牌，则 不能 :

However, if you want to match any two tokens other than A followed by B, you cannot do:

p : ~(A B) ;

就像词法分析器规则一样，您不能求反多个令牌.为此，您需要执行以下操作:

Just as with lexer rules, you cannot negate more than a single token. To accomplish the above, you need to do:

P
  :  A ~B
  |  ~A .
  ; 

请注意，解析器规则中的.(DOT)字符与词法分析器规则中的任何字符都 不 匹配.在解析器规则内部，它匹配任何令牌(在这种情况下为A，B，C，D或E).

Note that the . (DOT) char in a parser rules does not match any character as it does inside lexer rules. Inside parser rules, it matches any token (A, B, C, D or E, in this case).

请注意，您不能否定解析器规则.以下是非法的:

Note that you cannot negate parser rules. The following is illegal:

p : ~a ;
a : A  ;

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