[cello-devel] Cells II Functional Requirements

[Kenny Tilton]

Kenny Tilton wrote:

> Cells II seems to be OK, and is back at work running Cello as well as 
> passing its regression tests. It will be released when I figure out 
> whether to put everything up on the Cells or Cello project. I plan 
> from here out to focus more on developing a commercial title (using 
> Cello) than on porting Cello. This may mean I will not even look at OS 
> X until the commercial title is ready to go and I want the OS X 
> version (I will). This also means I want a very simple way to share my 
> ongoing work on Cello/Cells and the easiest will be to have one cvs 
> repository I update periodically.
>
> Anyway, for now, here is the spec which guided the Cells II rewrite:
>
> Suppose the application is at some steady state S in which all Cells
> (slots of instances) are either inputs (what I used to call c-variable)
> or have been computed from other Cells.
>
> Now the application polls a socket or OS event stream and gets a new 
> input, which leads to some cell X being assigned a new value.
>
> Suppose also the new value for X is different from the prior value 
> (according to a user-definable test). We now have not just a write 
> operation but also a semantically meaningful change to X, so we also
> consider a new state S+ to have been established, with X being the 
> only Cell to have reached state S+.
>
> Now suppose there exists some cell A which depends only on cell B 
> which depends only on X. Suppose also that when cell B gets recomputed 
> to reach state S+, the change test for B's new value indicates "no 
> change". Let us then say B is dependent on the change to X but 
> /unaffected/ by it. 

should be "A and B are dependent on but unaffected by the change to X".

kt