At 03:14 2/11/2008, =?ISO-8859-2?Q?Imre_Andr=E1s?= wrote:
>This compiles ok (I'm still wondering about the $type and token
>magic), but there is a problem with processing A ::= SEQUENCE {
>a, SEQUENCE, c} as input. A MismatchedTokenException occurs
>instead of treating SEQUENCE as an ID.
[...]
>tokens { SQ; }
[...]
>SEQUENCE : 'SEQUENCE';
[...]
>ID: ( SEQUENCE )=> SEQUENCE {$type = SQ;} | ('a'..'z'|'A'..'Z')+
>;
I missed the earlier part of this thread, so I'm not entirely sure
what you're trying to accomplish, but the above seems wrong.
First off, you're defining two top-level tokens that can match the
character sequence 'SEQUENCE': the SEQUENCE rule, which will
assign it the token type SEQUENCE, and the ID rule, which will
assign it the token type SQ (which you are not actually using
anywhere in your parser rules, so if it ever gets produced your
parser will have mismatched token errors).
If you want the ID rule to be the only source of matching for the
input text "SEQUENCE", then you need to make the SEQUENCE rule a
fragment and either change your parser rules to look for SQ
instead or to make the ID rule set the token type to SEQUENCE.
Alternatively (provided there aren't weird issues with lookahead)
you ought to be able to remove the SEQUENCE-matching clause from
ID entirely. The input text "SEQUENCE" should always generate a
SEQUENCE token without that clause in ID being present, so that
clause is just introducing ambiguity (though it does guarantee
full lookahead).
>How can I tell ANTLR that 'SEQUENCE' means a list when followed
>by '{', otherwise it is an ID?
This sounds like an entirely different problem than what the above
clause is trying to accomplish :)
There are two schools of thought on how to treat out-of-place
keywords as if they are just normal identifiers, and they're both
covered here:
<http://www.antlr.org/wiki/pages/viewpage.action?pageId=1741>http://www.antlr.org/wiki/pages/viewpage.action?pageId=1741
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