On 03/04/2011 03:02 AM, Olivier Lefevre wrote:
> Sorry, the subject is not very informational but I cannot
> get the hang of the problem, so I cannot devise a better
> subject. I have this small grammar:
>
> grammar Gr3;
>
> options { output=AST; }
>
> stat : fun1 | fun2 ;
> fun1 : 'fun1(' ID1 ')' ;
> fun2 : 'fun2(' ID2 ')' ;
>
> fragment DIGIT : '0'..'9' ;
> fragment LETTER : ('a'..'z' | 'A'..'Z') ;
>
> ID1 : (DIGIT | LETTER)+ ;
> ID2 : (DIGIT | LETTER | '_' | '-' | '.')+ ;
> WS : (' '|'\t')+ { skip(); } ;
>
> It can recognize, say, fun1(AB) and fun2(AB_CD) as expected
> but not fun2(AB), which should also be valid since AB matches
> both ID1 or ID2. Rewriting fun2 as
>
> fun2 : 'fun2(' (ID1 | ID2) ')' ;
>
> works but is not satisfactory because I want an ID2 as fun2
> argument, not an ID1. So, how can I force ANTLR to "consider"
> ID1 in this position?
The usual answer would be to rewrite ID1 and ID2 as:
fragment ID2 : ;
ID1 : ( DIGIT | LETTER | ( '_' | '-' | '.' ) { $type = ID2; } )
;
The problem is that if only ID2 types are legal in fun2, you might end
up with an ID1 in a fun2 which you would have to change the type of "on
the fly" to ID2, even though the token was lexed as ID1.
> Thanks,
>
> -- O.L.
I hope this helps....
--
Kevin J. Cummings
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