Go and look at the expression tree for say the Java.g example grammar. You will probably see that your expression tree is not formed correctly and that is one possibility for why you need the predicate (BTW, when you do need a predicate, don't specify the whole rule, use the minimum set of tokens that is required).
Specifically here, look at you unary operator and sort that out, then I suspect that you are not showing the whole thing here and your paren expression is clashing with something else higher up the chain, which is the other reason you use the predicate. Basically, you need to remove the predicate and fix the grammar problems that ensue once you remove it. Jim > -----Original Message----- > From: [email protected] [mailto:antlr-interest- > [email protected]] On Behalf Of Philippe Frankson > Sent: Wednesday, April 27, 2011 2:29 AM > To: [email protected] > Subject: [antlr-interest] Handling errors using syntactic predicate > > Hi, > > In my grammar, I can parse expression like this: > (A <= 1 or A >= 6) and (A not in (43,44)) > > Let's say, it is a kind of sql WHERE clause. > > Here is a part of the grammar to understand the problem: > > @rulecatch { > catch (RecognitionException re) { > if (this.errorMessage.isEmpty()) > this.errorMessage = this.getErrorMessage(re, > this.getTokenNames()) + " [pos: " + (re.charPositionInLine - > errorPosOffset) + "]"; > throw re; > } > } > > ... > > arithexpr: (arithterm ) ( > '+' arithterm | > '-' arithterm | > CONCAT arithterm)*; > > arithterm: (arithatom | '-' arithatom) > ('*' arithatom > | '/' arithatom)*; > > arithatom: arithvar > | ifthenelse > | constantorparameter > | floorexpr > | floatexpr > | leftexpr > | rightexpr > | replaceexpr > | dayexpr > | monthexpr > | yearexpr > | yearnoexpr > | (arithexprparen)=> arithexprparen > ; > > arithexprparen: '(' arithexpr ')'; > > > You can notice that I'm using syntactic predicate to support nested > expression with parenthesis. > > The problem is the following: > If I have a mistake in my expression like this: (A <= 1 or A >= 6xx) > and (A not in (43,44)) Where 6xx is the mistake, The error I have is: > 'no viable alternative at input 'A' [pos:1] This is because it doesn't > reach the right parentheses while parsing "(arithexprparen)=> > arithexprparen", so the error is triggered for the beginning of > arithatom evaluation. > I would have liked it to tell me that the problem is 'x' and not 'A'. > Is there any way to deal with that ? > > > Thanks a lot for any help. > Philippe > > > List: http://www.antlr.org/mailman/listinfo/antlr-interest > Unsubscribe: http://www.antlr.org/mailman/options/antlr-interest/your- > email-address List: http://www.antlr.org/mailman/listinfo/antlr-interest Unsubscribe: http://www.antlr.org/mailman/options/antlr-interest/your-email-address -- You received this message because you are subscribed to the Google Groups "il-antlr-interest" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/il-antlr-interest?hl=en.
