It seems very strange to have that as a lexer rule, defined as it is,
without knowing more about your specific use-case. It would make more
sense to me to have lexer rules for every different 'meaning' of symbols
and then have a parse rule for each combination you might want to use.
The reason I say this is simply in terms of the tokens that are
generated - it seems very odd to have a single token for all of those
symbols. Also, it looks like it leads to pretty hard-to-read grammars.
Sam
On 25/09/2011 14:04, ALEC LEE wrote:
>
> I have a lexer rule listing all the acceptable symbols:
>
> ALL_SYMBOLS: ('!' | '#' | '%' | '^' | '-' | '+' | '=' | '<' |'>' | ','
> | '.' |'?' | '/' | '*' ); // and more......
>
> But sometimes I also want a parser rule to match all symbols except say "!
> #", "+ =" or "+ - * /". Because I have different needs at different time, I
> want to specify a rule using ALL_SYMBOLS minus some symbols style. How
> should one write such a rule? Can semantic predicate achieve this?
>
> I've never used semantic predicate before. Are these the proper way to use
> it:
>
> all_symbols_except_hash_equal: ALL_SYMBOLS {"#=".indexOf($text)< 0 }? ; //
> can it be done this way? Can $text be used inside a semantic predicate?
> all_symbols_except_comma_plus_minus: {",+-".indexOf($text)< 0}?=>ALL_SYMBOLS
> ;
> // or should it be done this way? But $text seems not available inside a
> predicate and there is an failed predicate exception message printed in the
> screen
>
>
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