Hello, im a beginner in Antlr. Im trying to do a parser/lexer for arithmetic expressions. I took the beginner's example from the Getting Started with antlr, and modified it, for variable support. The .g file is this:

			

			options {
			

			language = "CSharp";
			

			}
			

			class CalcParser extends Parser;
			

			options {
			

			buildAST=true;
			

			}
			

			expr:   mexpr ((PLUS^|MINUS^) mexpr)*
			

			;
			

			mexpr
			

			:   atom ((STAR^|DIVIDE^) atom)*
			

			;
			

			atom:   INT
			

			|   LPAREN! expr RPAREN!
			

			| VARIABLE
			

			;
			

			

			class CalcLexer extends Lexer;
			

			options {
			

			k=2; // needed for newline junk
			

			charVocabulary='u0000'..'u007F'; // allow ascii
			

			}
			

			LPAREN: '(' ;
			

			RPAREN: ')' ;
			

			PLUS  : '+' ;
			

			MINUS : '-' ;
			

			STAR  : '*' ;
			

			DIVIDE : '/';
			

			INT   : ('0'..'9')+ ;
			

			VARIABLE
			

			: ('a'..'z'|'A'..'Z')+
			

			;
			

			WS    : ( ' '
			

			| '
			

			' '
			

			'
			

			| '
			

			'
			

			| ' '
			

			)
			

			{$setType(Token.SKIP);}
			

			;
			

			

			class CalcTreeParser extends TreeParser;
			

			options {
			

			importVocab=CalcParser;
			

			}
			

			

			expr returns [double r=0]
			

			{ double a,b; }
			

			:   #(PLUS  a=expr b=expr)  {r = a+b;}
			

			|   #(MINUS a=expr b=expr)  {r = a-b;}
			

			|   #(STAR  a=expr b=expr)  {r = a*b;}
			

			|   #(DIVIDE  a=expr b=expr)  {r = a/b;}
			

			|   i:INT                   {r = (int)Int32.Parse(i.getText());}
			

			|   j:VARIABLE                   {r = 2;}
			

			;
			

		

The parser is so cool, but give me a valid response with expressions like (a+b))-c, moreover if you enter (3+4))-3 you get a result equal to 7...