syntactic predicate question

[Ghislain Benrais]

Hello,
I have too small a brain to really understand grammars and ANTLR. But I love ANTLR because it saved my life a few times already. The enclosed grammar parses classical expressions (assignments, conditions and function calls) with one specific expression that I added with 'codeList' rule. This rule parses a shortcut to enumerate 'or' conditions :

x = 1-3,18

which means

x=1 or x=2 or x=3 or x = 18

Everything went fine until I I added the 'functionCall' rule, I got the warning :

Decision can match input such as "COMMA INT" using multiple alternatives

In rule codeList, I have tried to use a syntactic predicate :

codeList :       codeListElement  (((COMMA)=>COMMA|PLUS) codeListElement)*

But I still got the warning.
Then I tried a rule option :

codeList
options {greedy = true; }
        :       codeListElement  ((COMMA|PLUS) codeListElement)*
        ;

And it still displays the warning.
It is not an issue yet because it works anyway, but I would like to understand what went wrong with the syntactic predicate.
Thans a lot for your help,
Ghislain
PS : the purpose is to produce AST but I have not defined rewrite rules yet
PPS : The warning disappears if I add the grammar option 'backtrack=true' but then ANTLRworks interpreter doesn't work anymore

[Mike Lischke]

Hi Ghislain,

Everything went fine until I I added the 'functionCall' rule, I got the warning :

Decision can match input such as "COMMA INT" using multiple alternatives


In rule codeList, I have tried to use a syntactic predicate :

codeList :       codeListElement  (((COMMA)=>COMMA|PLUS) codeListElement)*


But I still got the warning.
Then I tried a rule option :

codeList
options {greedy = true; }
        :       codeListElement  ((COMMA|PLUS) codeListElement)*
        ;


Try marking the inner loop greedy (it is already greedy by default, but telling the parser that you know silences the warning), e.g

codeList:

codeListElement ( options {greedy = true;}: (COMMA | PLUS) codeListElement)*

;

Mike

-- 

www.soft-gems.net

[Ghislain Benrais]

Hello Mike,
Thank you four your answer but it didn't silence the warning.

codeList
    :    codeListElement  ( (options {greedy = true;}:COMMA|PLUS)! codeListElement)*
    ;

Yours,
Ghislain

[Jim Idle]

Try k=1 fir that rule?

Jim

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[Ghislain Benrais]

Hello Jim,
It didn't work.
Thanks,
Ghislain

[George S Cowan]

Hi, Ghislain,
I notice that your rule for codeList in your reply to Mike did not place the option exactly where he suggested. I personally think Mike's suggestion is very wierd, but he does sound like he knows what he's talking about.

Mike's: codeListElement  (  options {greedy = true;}:(COMMA|PLUS)  codeListElement)*
yours : codeListElement  ( (options {greedy = true;}: COMMA|PLUS)! codeListElement)*

 - George

[Ghislain Benrais]

Hello George,
Thanks a lot, no more warning, great.
Yours,
Ghislain

Le samedi 23 février 2013 21:10:17 UTC+1, George S Cowan a écrit :

Hi, Ghislain,
I notice that your rule for codeList in your reply to Mike did not place the option exactly where he suggested. I personally think Mike's suggestion is very wierd, but he does sound like he knows what he's talking about.

Mike's: codeListElement  (  options {greedy = true;}:(COMMA|PLUS)  codeListElement)*
yours : codeListElement  ( (options {greedy = true;}: COMMA|PLUS)! codeListElement)*

 - George

On Wednesday, February 13, 2013 9:08:51 AM UTC-5, Ghislain Benrais wrote: