computing cumulative sum in an expression and storing it for further calculations

[#1]

Hi

How can I compute cummulative sum and store it in an expression? and I would like to use that expression for further computation.

date           $(value)

1/1/2011     5

1/2/2011     10

1/3/2011     8

The expression should yield

date          newexpression

1/1/2011     5

1/2/2011     15

1/3/2011     23

Note: the columns value is an expression

I dont want to

($(value)+if(isnull(above("newexpression")),0,above("newexpression")))

This works fine only if i have a column called newexpression in my straightable. But i dont want to have this as a column, I want to be able to store this in an expression and i have to do further computation.

what should I be doing instead?