private void arith_op() throws Exception
    {
        if(currentToken.getType()==token.OP_SUM ||currentToken.getType()==token.OP_RESTA ||
           currentToken.getType()==token.OP_MULTIPLICACION || currentToken.getType()==token.OP_DIVISION ||
           currentToken.getType()==token.OP_MOD || currentToken.getType()==token.OP_SHIFTLEFT ||
           currentToken.getType()==token.OP_SHIFTRIGHT)
        {
            currentToken=lex.getNextToken();
        }else
        {
            throw new Exception("Se esperaba un operador aritmetico");
        }
    }