[antlr-interest] Simple expression grammar

[Maciej Bakalarz]

Hi again!
>> 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 )"
>>
> What happens if you change this:
>>
>> expression
>>     : ALFANUM
>>     ;
> 
> to this:
> 
>  expression
>       : ALFANUM | '(' prog ')'

It's good idea. I will try it for a moment. For now I used '('prog')' 
but in other part of grammar.
I also used mentioned "backtrack=true; memoize=true;" option.
I added possibility to negate expressions too ...
It's not tested but seems to work fine.

Here is the final grammar:

grammar GuardCondition;

options {
     output=AST;
     ASTLabelType=CommonTree;
backtrack=true;
memoize=true;
}

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)*
	| LPAREN! prog RPAREN!
	| NEG^ LPAREN! prog RPAREN!	
	;
expression
	: ID | INT | NEG^ ID
	;

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


Thanks for help !
Maciek Bakalarz