A stab at the sealer in E

[Ka-Ping Yee]

On Wed, 3 Nov 1999, Marc Stiegler wrote:
>
> ? def sealSystemMaker new() : any {
> >     def privateCurrentContent := null
> >     def sysUnsealer unseal(box) : any {
> >         privateCurrentContent := null
> >         box offerContent
> >         def content := privateCurrentContent
> >         privateCurrentContent := null
> >         content
> >     }
> >     def boxMaker new(message) : any {
> >         def box {
> >             to offerContent {
> >                 privateCurrentContent := message
> >             }
> >         }
> >     }
> >     def sysSealer seal(message) : any {boxMaker new(message)}
> >     [sysSealer,sysUnsealer]
> > }

Very interesting!  I would have avoided doing something like
this for fear of a race condition when attempting to unseal
two different envelopes made by the same sealer -- but
with E's event model i guess this isn't a problem, is it?
This makes it a good example for your class. :)

I suppose you could call mine the "coat-check model" (you
get a unique token) in contrast to this "locked-box model"
(the unsealer has special access to get the content out of
the envelope).  I believe you are correct about the garbage
collection -- when you run a coat check, there's always
the problem of not knowing when people will come back to
get their coats.  So i think yours is the best solution.

This is eerily reminiscent of the alternative to EQ that
Dean proposed...


-- ?!ng

"The biggest cause of trouble in the world today is that the stupid people
are so sure about things and the intelligent folk are so full of doubts."
    -- Bertrand Russell