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Antlr cannot find symbol

I'm working on an ANTLR project that should basically implement this simple grammar:

WS  :   ' '
    ;


MINUS   : '-'   ;



DIGIT  :   '0'..'9'
    ;

int4    
@init{
 int n = 0;
}
:     (({n<4}?=> WS {n++;})* (MINUS{n++;})?({n<4}?=> DIGIT{n++;})*){n==4}?      ;



numbers
    :   (int4)*;

int4 follow the format I4 of Fortran (stands for an integer with width four)

this code are giving me the following errors:

[10:17:20] C:\Users\guille\Documents\output\testParser.java:277: cannot find symbol
[10:17:20] symbol  : variable n
[10:17:20] location: class testParser
[10:17:20]                     if ( (evalPredicate(n==4,"n==4")) ) {
[10:17:20]                                         ^
[10:17:20] C:\Users\guille\Documents\output\testParser.java:283: cannot find symbol
[10:17:20] symbol  : variable n
[10:17:20] location: class testParser
[10:17:20]                 else if ( (LA4_0==WS) && (evalPredicate(n<4,"n<4"))) {
[10:17:20]                                                         ^
[10:17:20] C:\Users\guille\Documents\output\testParser.java:289: cannot find symbol
[10:17:20] symbol  : variable n
[10:17:20] location: class testParser
[10:17:20]                 else if ( (LA4_0==DIGIT) && (evalPredicate(n<4,"n<4"))) {
[10:17:20]                                                            ^
[10:17:20] 3 errors

Any Idea?

Solution

  • The local variable n does no get passed to the location where the predicates get evaluated. You need to define a scope which can be used inside the predicates:

    int4
scope { int n; }
@init { $int4::n = 0; }
 : ( {$int4::n < 4}?=> WS {$int4::n++;} )*
   ( MINUS {$int4::n++;} )?
   ( {$int4::n < 4}?=> DIGIT{$int4::n++;} )*
   {$int4::n == 4}?
 ;

    Related:

    For a better understanding, look at the generated source code of your grammar, and the generated code of the grammar using the scope.