Hidden token into default channel - AntlrV3

Suppose I'm havin开发者_开发技巧g white spaces (WS) in the hidden channel. And for a particular rule alone, I want white spaces also to be considered, is it possible to bring WS to the default channel for that particular rule alone in the parser?

Have look at the answer for your path question, notice how I put a '\n' into the parser rule. You should be able to put ' ' as well. Now, do all the options for your WS on the hidden channel need to be in the rule would be the only concern.

eg

rulename : Token1 ' ' Token2 ' ' Token1 {place action here};

Please note that the rule name starts with a lowercase letter and it is a parser rule while the "Token#" start with uppercase letter and are lexer rules. In between the different tokens the rule requires a space in this example, and I suppose you could put something like (' '|'\t'|'\r'|'\n')+ but I have not tried this and will leave that for you to attempt.

You can always query the hidden token stream

ie in C++

myrule: MYTOK { static_cast<antlr::CommonHiddenStreamToken*>(LT(1).get())->getHiddenAfter()->getType() == WS}? MYTOK 

The semantic predicate will check to see if there is a whitespace token after matching the lexical token MYTOK

Lexer rules are evaluated in the order they are listed in your grammar file.

This means you can have something like this:

STRING_LITERAL: '"' NONCONTROL_CHAR* '"';   


fragment NONCONTROL_CHAR: LETTER | DIGIT | UNDERSCORE |  SPACE | BACKSLASH | MINUS | COMMA;
fragment LETTER: LOWER | UPPER;
fragment LOWER: 'a'..'z';
fragment UPPER: 'A'..'Z';
fragment DIGIT: '0'..'9';
fragment SPACE: ' ' | '\t';
fragment UNDERSCORE: '_';   
fragment MINUS:  '-';
fragment BACKSLASH: '\\';

COMMA: ',';     

NEWLINE: ('\r'? '\n')+ { $channel = HIDDEN; };
TERMINATOR  : ';';


WHITESPACE: SPACE+ { $channel = HIDDEN; };

LINE_COMMENT
    :   
    '//' ~('\n'|'\r')*  ('\r\n' | '\r' | '\n') 
    {
        $channel = HIDDEN;
    }
    |   
    '//' ~('\n'|'\r')*     
    {
        $channel = HIDDEN;
    }
    ;   

As you can see a string literal can have space or tabs in it. However a stand alone space or tab will be sent to the HIDDEN channel.