[antlr-interest] please help on simple parser antlr v3

[Thomas Brandon]

I don't think Antlr v3 yet allows you to suppress warnings so these are
unavoidable. You want to check that Antlr is behaving correctly and ignoring
the correct alternatives. As you have no actions it does not matter which
alternative Antlr takes, and it is correctly handling your grammar so you
can ignore the warnings.
I don't think there is any way to refactor out the remaining ambiguity.
Removing the WS rule was correct. It is not needed as it is duplicated by
the ~('\'') alternative, but the ambiguity between '\n' and '\r'('\n')? is
unavoidable, though ideally you would supress the warning.

Tom.
On 9/27/06, Michiel Vermandel <Michiel_Vermandel at axi.be> wrote:
>
>
> Sorry,
>
> It would have been better to test the grammar first without the WS rule in
> the QOUTES_STRING rule since I still get warnings (less though) and now I
> can't
> figure out how to solve this.
> Can someone please tell me how to prevent the *multiple alternatives *
> warnings?
>
> ------------------------new grammar---------------------------
>
> grammar TestParser;
> options {k=2; backtrack=true; memoize=true;}
>
>
> statement: identifier | quoted_string ;
>
> identifier:         IDENTIFIER;
>
> quoted_string: QUOTED_STRING;
>
>
> fragment
> AZ_CHAR: 'a' .. 'z' | 'ç' | 'é' | 'è'| 'ê'  | 'à';
>
> fragment
> SPECIAL_CHAR: '_' | '$' | '#' ;
>
> fragment
> ANY_CHAR: AZ_CHAR | SPECIAL_CHAR;
>
> IDENTIFIER:  ( AZ_CHAR | (N)+)  ANY_CHAR  (ANY_CHAR | N)*;
>
> N:  ('0' .. '9')+;
>
> WS        :        (' '
>                 |        '\t'
>                 |        ('\n'|'\r'('\n')?)
>                 )+
>         { channel=99; };
>
> QUOTED_STRING: '\'' (  ~('\'') | '\'' '\'' )* '\'';
>
> --------------------remaining warnings---------------------------------
>
> [14:26:53] test1.g:28:15: Decision can match input such as "'\n'" using
> multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
> [14:26:53] C:\Documents and Settings\mvrm\My
> Documents\Antlr\grammars\test1.g:28:15: Decision can match input such as
> "'\n'" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
>
>
>
>
>
>
>
>
> Hi,
>
> I started converting my v2 grammars to v3 and ran against some warnings
> when generating code for a very simple test grammar.
> Below, you find the parser, followed by the warnings.
> This grammar is a part of a grammar in v2 which I am converting.
>
> In v2 the rule QUOTED_STRING was:
>
> QUOTED_STRING: '\'' ( WS | '\'' '\'' | ~('\'') )* '\'';
>
> Now in v3 I get this list of warnings (see below).
> In v2 the WS was needed in the QUOTED_STRING rule in order to increment
> the line counter properly.
> I think I can solve the warnings by leaving out the WS rule since in Antlr
> v3 I do not need to bother about incrementing the line counter.
>
> So, Can please someone confirm that I am right in just leaving out the WS
> rule from the QUOTED_STRING rule?
>
> Thanks!
>
>
> ---------------------------------------------------------------------
>
>
> grammar TestParser;
> options {k=2; backtrack=true; memoize=true;}
>
>
> statement: identifier | quoted_string ;
>
> identifier:         IDENTIFIER;
>
> quoted_string: QUOTED_STRING;
>
>
> fragment
> AZ_CHAR: 'a' .. 'z' | 'ç' | 'é' | 'è'| 'ê'  | 'à';
>
> fragment
> SPECIAL_CHAR: '_' | '$' | '#' ;
>
> fragment
> ANY_CHAR: AZ_CHAR | SPECIAL_CHAR;
>
> IDENTIFIER:  ( AZ_CHAR | (N)+)  ANY_CHAR  (ANY_CHAR | N)*;
>
> N:  ('0' .. '9')+;
>
> WS        :        (' '
>                |        '\t'
>                |        ('\n'|'\r'('\n')?)
>                )+
>        { channel=99; };
>
> QUOTED_STRING: '\'' ( WS | '\'' '\'' | ~('\'') )* '\'';
>
>
> -------------------------------------------------------------------------------
>
> [14:09:37] test1.g:28:15: Decision can match input such as "'\n'" using
> multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
> [14:09:37] test1.g:32:48: Decision can match input such as "' '" using
> multiple alternatives: 1, 3
> As a result, alternative(s) 3 were disabled for that input
> [14:09:37] test1.g:32:48: Decision can match input such as "'\t'" using
> multiple alternatives: 1, 3
> As a result, alternative(s) 3 were disabled for that input
> [14:09:37] test1.g:32:48: Decision can match input such as "'\r'" using
> multiple alternatives: 1, 3
> As a result, alternative(s) 3 were disabled for that input
> [14:09:37] test1.g:32:48: Decision can match input such as "'\n'" using
> multiple alternatives: 1, 3
> As a result, alternative(s) 3 were disabled for that input
> [14:09:37] C:\Documents and Settings\mvrm\My
> Documents\Antlr\grammars\test1.g:28:15: Decision can match input such as
> "'\n'" using multiple alternatives: 1, 2
> As a result, alternative(s) 2 were disabled for that input
> [14:09:37] C:\Documents and Settings\mvrm\My
> Documents\Antlr\grammars\test1.g:32:48: Decision can match input such as "'
> '" using multiple alternatives: 1, 3
> As a result, alternative(s) 3 were disabled for that input
> [14:09:37] C:\Documents and Settings\mvrm\My
> Documents\Antlr\grammars\test1.g:32:48: Decision can match input such as
> "'\t'" using multiple alternatives: 1, 3
> As a result, alternative(s) 3 were disabled for that input
> [14:09:37] C:\Documents and Settings\mvrm\My
> Documents\Antlr\grammars\test1.g:32:48: Decision can match input such as
> "'\r'" using multiple alternatives: 1, 3
> As a result, alternative(s) 3 were disabled for that input
> [14:09:37] C:\Documents and Settings\mvrm\My
> Documents\Antlr\grammars\test1.g:32:48: Decision can match input such as
> "'\n'" using multiple alternatives: 1, 3
> As a result, alternative(s) 3 were disabled for that input
>
>
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