[Oz] Multiple evaluation question

[Denys Duchier]

khoxsey at ix.netcom.com (Kent Hoxsey) writes:

> My model has a rule that says a certain two of the attributes of an item
> cannot be the same, which I define as a reified constraint:
> 
> declare X Y R in {FD.decl X} {FD.decl Y} R::0#1
> R = (X \=: Y)
> 
> Now imagine I have two items, each with two attributes:
> 
> A = item(attr1:1 attr2:2)
> B = item(attr1:1 attr2:1)
> 
> What I would like to do is to apply a procedure to item A, save the
> value of R, and then apply the procedure to item B and again save the
> value of R.

This is what abstractions are for:

	declare Rs = {Map [A B] fun {$ I} I.attr1\=:I.attr2 end}

Now Rs contains a list of boolean variables resulting from evaluating
the reified constraint for each item.

However I wonder why you are using a reified constraint.  If the only
valid models of your problem are those where the attributes are
different, then why not just pose this constraint.

	{ForAll [A B] proc {$ I} I.attr1\=:I.attr2 end}

Am I misunderstanding your problem? Also, your example above has items
with determined attributes; in that case, of course, constraints are
pointless since there is nothing to be constrained.

I hope this helped.  The "Finite Domain Constraint Programming
Tutorial" is also well worth reading; it has loads of examples that
may help clarify things a bit.

Sincerely,

-- 
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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