[antlr-interest] Simple expression grammar

[Maciej Bakalarz]

Hi !

I am newbie to ANTLR. I am trying to make very simple grammar which will 
be used to build AST for Guard Condition expressions. Guard Conditions 
expression are used as a labels in automata transitions.

This is my grammar:

grammar GuardCondition2;

options {
     output=AST;
     ASTLabelType=CommonTree;
}

prog:
	logical_or_expression+
	;

logical_or_expression:
	logical_and_expression (OR_OP^ logical_and_expression)*
	;

logical_and_expression
	: rel_expression (AND_OP^ rel_expression)*
	;

rel_expression
	: expression (REL_OP^ expression)*
	;
expression
	: ALFANUM
	;

LPAREN 	:	'(' ;
RPAREN	:	')' ;
REL_OP   	: 	 '==' | '<' | '>' | '<=' | '>='|'!=' ;
OR_OP 	: 	'||' ;
AND_OP 	:	 '&&' ;
ALFANUM 	: 	(ID|INT)+;
ID  	:  	 ('a'..'z'|'A'..'Z')+ ;
INT 	:  	 '0'..'9'+ ;
WS  	:   	(' '|'\t')+ {skip();} ;


This grammar is working fine. Using this grammar I can parse expressions 
like "a>=3 || b<=4 && c>=4".

I need to parse expressions which are using nested parenthesis, like:
"( a>=3 || b<=4 ) && c>=4" or "((a>=3 || b<=4) && c>=4) || a>=3 )"

I wast trying to modify grammar to achieve this goal but I it always 
came up that I am using Left Recursion.

Does anybody knows how to modify grammar so nested parenthesis would be 
possible ?

Thank You,
Maciek Bakalarz