[antlr-interest] Disambiguate following rules

[Jost Baron]

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Hi!

The problem is that an expression might be an identifier, oder maybe
an assignment. So both possibilities may match the same input.

To resolve that, you would usually use left-factoring, but that seems
impractical here.

Another solution might be to remove the second alternative from the
var_decl rule. Why would you have an expression as variable name? I
don't know your language and reasons for that rule, of course.

Greetings,
Jost

On 10/28/2012 09:26 AM, forumer at smartmobili.com wrote:
> Hi,
> 
> I have a grammar with the following rules and that is using 
> backtrack option. Now when I remove backtrack I have a problem
> with the var_decl rule :
> 
> Decision can match input such as "IDENTIFIER" using multiple 
> alternatives: 1, 2
> 
> 
> Any idea about how to fix this ?
> 
> 
> 
> variable_declaration : VAR variable_declaration_list | 
> empty_statement ;
> 
> variable_declaration_list : var_decl ( ',' var_decl )* ;
> 
> 
> var_decl : identifier ( '=' expression )? | expression ;
> 
> /***EXPR*************************/ expression : 
> assignment_expression (',' assignment_expression )* ;
> 
> argument_expression_list : assignment_expression ( ',' 
> assignment_expression )* ;
> 
> assignment_expression : conditional_expression ( 
> assignment_operator assignment_expression )? ;
> 
> assignment_operator : '=' | '*=' | '/=' | '%=' | '+=' | '-=' | 
> '<<=' | '>>=' | '&=' | '^=' | '|=' | '>>>=' ;
> 
> constant_expression : conditional_expression ;
> 
> conditional_expression //: logical_or_expression  ( '?' 
> logical_or_expression ':' logical_or_expression )? : 
> logical_or_expression  ( '?' expression ':' expression )? ;
> 
> logical_or_expression : logical_and_expression ('||' 
> logical_and_expression )* ;
> 
> logical_and_expression : inclusive_or_expression ('&&' 
> inclusive_or_expression )* ;
> 
> inclusive_or_expression : exclusive_or_expression ('|' 
> exclusive_or_expression )* ;
> 
> exclusive_or_expression : and_expression ('^' and_expression)* ;
> 
> and_expression : equality_expression ('&' equality_expression)* ;
> 
> equality_expression /* === and !== for javascript */ : 
> relational_expression (('!=' | '==' | '===' | '!==' ) 
> relational_expression)* ;
> 
> relational_expression /* instanceof and in are for javascript */ : 
> shift_expression ( RELATION_OPERATOR shift_expression)* ;
> 
> RELATION_OPERATOR :  '<' | '>' | '<=' | '>=' | 'in' | 'instanceof' 
> // Don't tokenize these! ;
> 
> shift_expression : additive_expression (('<<' | '>>') 
> additive_expression)* ;
> 
> additive_expression : multiplicative_expression (('+' | '-') 
> multiplicative_expression)* ;
> 
> multiplicative_expression : unary_expression ( ('*' | 
> REGEX_OR_DIVIDE | '%') unary_expression )*    /* no cast
> expression for objj */ ;
> 
> unary_expression : postfix_expression | '++' unary_expression | 
> '--' unary_expression | unary_operator unary_expression   /* no 
> cast expression for objj */ ;
> 
> unary_operator //    : '&' | '*' | '+' | '-' | '~' | '!' : '+' | 
> '-' | '~' | '!' ;
> 
> postfix_expression : primary_expression ( '[' ']' | '[' expression 
> ']' | '(' ')' | '(' argument_expression_list ')' | '.' identifier
> | '++' | '--' )* ;
> 
> primary_expression : TRUE | FALSE | 'defined' '(' expression ')' /*
> for prepocessing */ | TYPEOF identifier                 /* 
> javascript */ | TYPEOF '(' identifier ')'         /* javascript */
>  | '[' expression? ']'     /* objj array? DIES */ | '[' expression 
> ',' expression ( ',' expression )* ']'   /* objj array? DIES */ | 
> message_expression        /*   '[' receiver message_selector ']' */
> | selector_expression | protocol_expression | encode_expression |
> '{' STRING_LITERAL ':' primary_expression ( ','  STRING_LITERAL ':'
> primary_expression )* '}'  /* js obj array? */ | '{' '}' /* js
> empty obj array? */ | constant | identifier | VAR identifier | '('
> expression ')' ;
> 
> 
> identifier : a=IDENTIFIER { /*System.out.println ($a.text);*/ } ;
> 
> IDENTIFIER : 
> ('_'|'A'..'Z'|'a'..'z')('_'|'A'..'Z'|'a'..'z'|'0'..'9')* ;
> 
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