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

[Michiel Vermandel]

Hi Tom,

Thanks for your explanation.
I made some extra lexer rules and I succeeded in eliminating the warnings.
Though I'm not sure my grammar is still correct and I don't understand why 
this solution does not generate the warnings.

Do you have any idea?

Thanks!

-------------------------grammar with no warnings-----------------------

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')+;

LF      :       '\n' { channel=99; };

CRLF    :       '\r' ('\n')? { channel=99; };

TAB     :       '\t' { channel=99; };

WS      :       (' '
                | TAB
                | CRLF
                | LF
                )+
        { channel=99; };
 
QUOTED_STRING: '\'' (  ~('\'') | '\'' '\'' )* '\'';

DOUBLE_QUOTED_STRING: '"' ( '""' | ~('"') )* '"'; 









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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