code: public GroovyExpression generateArithmeticExpression(GroovyExpression left, String operator,
              GroovyExpression right) throws AtlasException {
          ArithmeticOperator op = ArithmeticOperator.lookup(operator);
          return new ArithmeticExpression(left, op, right);
      }
docs: Generates an arithmetic expression, e.g. a + b