Using dimension value in expression

[#1]

Hello!

I have dimension Month and "sales per month" expression. I also want two more expressions:

first - Sum of all previous sales prior to month start

second - Sum of all previous sales prior to month end

I think expressions should be like

Sum({<SalesDate={"<monthstart(Month)"}>} Sales)

Sum({<SalesDate={"<monthend(Month)"}>} Sales)