Is there a repository for expressions

Forgive me if there's an obvious answer for this.
I was wondering if there was the facility to save expressions that
you would use in multiple reports. The ones we're looking at
specifically
create a value in a detail line by doing arithmetic on other detail
column values.The simplest way is to write a simple assembly and put the logic there.
Then you reference this assemby from your reports and use a
=myAssembly.myFunction(param1, param2) type syntax in the textbox.
If your assembly only performs calculations or other simple procedures,
you don't have to worry about code access security. There is
docmentation on this in MSDN.
jensisql