[cells-devel] Newbie questions

[Kenny Tilton]

rpgoldman at real-time.com wrote:

>>>>>>"Kenny" == Kenny Tilton <ktilton at nyc.rr.com> writes:
>>>>>>            
>>>>>>
>
>    Kenny> Mike J. Bell wrote:
>
>[...snip...]
>
>    Kenny> Cells have always grown in response to application
>    Kenny> requirements, so if someone comes up with a good example I
>    Kenny> will gladly look at implementing cycles in Cells. The
>    Kenny> question is, how can a = f(b) and b=f(a) ever be computed?
>    Kenny> In your example, there is no real cycle, because you are
>    Kenny> saying: "dollars is a function of yen /when changes/, and
>    Kenny> yen is a function of dollar /when dollar changes/." Only
>    Kenny> one can be changing at a time, so there is no cycle as the
>    Kenny> problem is conceived.
>
>    Kenny> But how is an instance initialized? I can supply conversion
>    Kenny> rules for dollar-balance and yen-balance, but how do I get
>    Kenny> the intial balance in there? I would need to specify a
>    Kenny> starting value, but for which one?  Both? What if I specify
>    Kenny> 1 for both? That conversion would be wrong, the dollar is
>    Kenny> (for now) worth more than 1 yen.
>
>    Kenny> Conceivably the answer is to let the programmer worry about
>    Kenny> it. I could specify a value (and the conversion rule) for
>    Kenny> dollar-balance and specify "unbound" and a rule for all
>    Kenny> other currencies. Then if the others get accessed, the
>    Kenny> system just calculates as usual. If all values are unbound
>    Kenny> a runtime error results. If the programmer specifies
>    Kenny> inconsistent initial values they get a wrong result (which
>    Kenny> we might be able to detect at some point of runtime) until
>    Kenny> some SETF perturbs the model and the formulas kick in to
>    Kenny> make things consistent.
>
>    Kenny> Thoughts on this?
>
>IIRC, Garnet's KR has a mechanism (one might call it "a cheap hack")
>to solve the problem of cyclic dependencies, which was to allow you to
>"plonk" an initial value into a slot that would be used to kick the
>whole mess off.
>
Yes. I was frankly horrified by all the backdoor hacks KR allowed. I 
must be getting old and stodgy.

:)

kenny