[antlr-interest] Problem with grammar

Matt Fowles matt.fowles at gmail.com
Sat Mar 19 06:12:14 PDT 2011


Wojciech~

Try pulling out the common left factor from your term expression:

term  : factor (('*'|'/'|'*') term)?;

Matt



On Sat, Mar 19, 2011 at 12:18 PM, Wojciech Tomasz Cichon
<wtcichon at googlemail.com> wrote:
> i’m struggling with this grammar for a few days now, and nothing really working,
> so i started from beginning and i have :
> grammar myGrammar;
>
> options {
>  language = Java;
>  k=1;
> }
>
> rule: term ;
>
> factor  :  '-'? NUMBER
>       ;
>
> term  : factor '*'  term
>      | factor '/'  term
>      | factor '%'  term
>      | factor;
>
>
>
> NUMBER :  '0'..'9'+
>    ;
> WS  :   ( ' '
>        | '\t'
>        | '\r'
>        | '\n'
>        ) {$channel=HIDDEN;}
>    ;
>
>
> and i got errors:
> warning(200): /ANTLR_TEST/myGrammar.g:13:7: Decision can match input such as "'-'" using multiple alternatives: 1, 2, 3, 4
> As a result, alternative(s) 2,3,4 were disabled for that input
> |---> term  : factor '*'  term
>
> warning(200): /ANTLR_TEST/myGrammar.g:13:7: Decision can match input such as "NUMBER" using multiple alternatives: 1, 2, 3, 4
> As a result, alternative(s) 2,3,4 were disabled for that input
> |---> term  : factor '*'  term
>
> error(201): /ANTLR_TEST/myGrammar.g:13:7: The following alternatives can never be matched: 2,3,4
> |---> term  : factor '*'  term
>
> can anyone tell me what i’m doing wrong
> regards
>
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