[Oz] equality of unbound variables

[Denys Duchier]

Hi Cesare,

I am now back from vacation.  Here is my belated answer to your last
message.

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

> My only concern is that, as I understand it, the approach you highlight
> above still requires for a term to be known in advance (at compile time,
> that is) to be encapsulated. I don't quite understand how to use the
> encapsulation technique with terms that are only known at run time, for
> instance because they are passed as input.
> Well, if the term is passed as a string, it is fairly straightforward to
> wrap it into a function definition (with the proper local variable
> definitions), feed it to Compiler.virtualStringToValue say, and get its
> encapsulated version.

For input, as you suggest, this is not an issue.  Personally, I often
use Gump to define an application specific language/notation when that
is more convenient.  In your case, I don't know if that would be a
worthwhile gain: input is supposed to be a predicate rather than a
bare term.  Instead of:

        forall X . f(X X)

the user supplies

        fun {$} X in f(X X) end

i.e. this is the same as:

        proc {$ T}
          T={MakeTuple f 2}
          T.1 = T.2
        end

a special purpose notation may allow an implicit quantification
(convenient), but then does not support a notion of scope
(inconvenient).

> What I don't see is how to encapsulate an Oz record at run time.

You would never have a non-encapsulated term, except within an
encapsulated computation which results in an encapsulated term.  In
fact, you suggest this yourself:

> But again, maybe I'm thinking in the wrong terms. Maybe there
> is a way to design any Oz application from the outset so that "run-time
> encapsulation" will never be needed.

If you have a practical example where you have difficulty seeing how
to preserve encapsulation, please let me know and I'll be happy to
suggest how to modify your design.

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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