[Stackless] Re: Stackless Python Logic Variables?

Jim Bowery janotforboweryspam at earthlink.net
Thu Jun 12 01:13:30 CEST 2003


"Peter Van Roy" <pvr at info.ucl.ac.be> wrote in message
> On Wed, 11 Jun 2003, Denys Duchier wrote:
> > jabowery at technicalpursuit.com (James A. Bowery) writes:
> > >> >     Stackless Python [1] is an ideal environment within which to
> > >> >     implement logic variables for thread synchroniziation [2].
> > >> >     The 3 additions required for this are 1) the addition of the
> > >> >     "unknown" keyword that declares a logic variable, 2) the
> > >> >     "final" keyword that declares a logic variable to be single-
> > >> >     assignment and 3) the "=:=" operator that performs a
> > >> >     unification of a logic variable with an expression.
> > I don't think that would be the way to do it.  This just doesn't fit
> > the Python way.
> >     Q. What is the expected benefit?
> >     A. Transparent synchronization on data.
> > In this regard, the better generalization (which for us was started in
> > Mozart and pursued in Alice) is the dual notion of future/promise and
> > does not apeal to the notion of logic variable nor of unification.

Well it sounds like you're (Denys Duchier) saying two, not-necessarily-
incompatible things:

1)  Logic variables aren't the "Python way".
2)  Logic variables aren't the "Alice way".

> Exactly.  If all you want is dataflow synchronization, then full logic
> variables are not needed.

To Peter Van Roy:

Ah, but it isn't "all you want to do" when distributed multiuser
environments are performing transactions.  Sometimes, more frequently than
idealized IDEF charts with associated Petri nets would imply, you want
toallow others to set something that you were intending on setting -- if you
got around to it.

Since a great deal of the real world consists of resolving such
indeterminacy, full logic variables seem valuable if they can be efficiently
implemented -- and your paper states they can.


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