[e-lang] Vat figure

Karp, Alan H alan.karp at hp.com
Mon Jun 20 20:50:12 EDT 2005

> -----Original Message-----
> From: e-lang-bounces at mail.eros-os.org 
> [mailto:e-lang-bounces at mail.eros-os.org] On Behalf Of David Hopwood
> Sent: Monday, June 20, 2005 2:14 PM
> To: Discussion of E and other capability languages
> Subject: Re: [e-lang] Vat figure
> Karp, Alan H wrote:
> > After seeing Ping's figures and reading the comments about them,  I
> > think truth is getting in the way of clarity.  Why not 
> describe the data
> > structure as a dequeue?  If you do, then you can say that immediate
> > calls put items at the head of the dequeue and eventual 
> sends put them
> > at the tail.  I think both the picture and the explanation 
> get simpler.
> I would find this less clear. In the current picture, each column
> represents a turn. Understanding turns, and the fact that only
> immediate sends occur within a turn, is crucial to understanding
> the model.

This was MarkM's objection, too, but I'm not so sure.  If an immediate
invocation can only put something on the head of the dequeue, and an
eventual message can only go on the tail of the dequeue, there's no way
for immediate messages to interleave with each other or with eventual
messages.  That's the essential point.  You don't even need the concept
of a turn.  We can even explain it in terms of MarkM's example of a
to-do list.  Items go either on the top or the bottom.
> -- 
> David Hopwood <david.nospam.hopwood at blueyonder.co.uk>
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Alan Karp
Principal Scientist
Virus Safe Computing Initiative
Hewlett-Packard Laboratories
1501 Page Mill Road
Palo Alto, CA 94304
(650) 857-3967, fax (650) 857-7029
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