[Oz] equality of unbound variables

[Denys Duchier]

tinelli at cs.uiowa.edu (Cesare Tinelli) writes:

> > What you want to do sounds very much like a Prolog trick.
> 
> Well, what you suggest below looks a lot like an Oz trick instead :)

It may look that way, but it has the advantage of being on secure
semantic ground.

The usual way to do in Oz what I think you want to do is by a
combination of what Christian and I described: I'll call this an
"encapsulated term".  An "encapsulated term" is represented by a
function.  Invoking the function creates a new "clone" of said term.
All operations on encapsulated terms are effected in new computational
spaces and return new encapsulated terms.  Here is an example:

Let's say F1 and F2 are two encapsulated terms and R is a function
that takes two terms and returns a new one (this might be an
inference).  Here is how to obtain the new encapsulated conclusions
that follow from F1 and F2 by R:

declare L = {Search.allP proc {$ T3} {R {F1} {F2} T3} end 1 _}

L is now a list of encapsulated terms.  This is the technique that we
used to implement e.g. a number of natural language parsers (in
particular chart parsers).

The constraint programming / search aspect of Oz were designed around
the notion of encapsulation.  The implementation supports this _very_
efficiently; more efficiently (and correctly) than what you are likely
to achieve by programming it yourself :-)

To really use Oz effectively, it is best to buy into its paradigm.
That's why I would like to encourage you to consider using
"encapsulated terms" if at all appropriate for your application.  You
will find they make your life a lot easier :-)

Cheers,

-- 
Dr. Denys Duchier			Denys.Duchier at ps.uni-sb.de
Forschungsbereich Programmiersysteme	(Programming Systems Lab)
Universitaet des Saarlandes, Geb. 45	http://www.ps.uni-sb.de/~duchier
Postfach 15 11 50			Phone: +49 681 302 5618
66041 Saarbruecken, Germany		Fax:   +49 681 302 5615
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