[Oz] equality of unbound variables

[Nils Franzen]

Cesare Tinelli wrote:

> I've been struggling to come up with a simple solution to the
> (supposedly) simple problem below. Any suggestions will be appreciated.
> 
> Consider a tuple T, some of whose arguments are unbound variables,
> possibly with repetitions; for instance, something like T=t(X Y X Z Z).
> I want to create a fresh ``variant'' of T in the sense of unification
> theory, that is, a copy of T in which all of T's unbound variables are
> (bijectively) renamed to fresh variables. For instance, in the example
> above, I'd like to produce a tuple of the form  t(X1 Y1 X1 Z1 Z1) where
> X1, Y1, Z1 are fresh variables.
> 
> Initially I thought of using {Record.clone T}, or similar methods,  to
> produce a tuple T1 of the form t(V1 V2 V3 V4 V5), and then identify T1.i
> with T1.j  for all i and j such that T.i and T.j coincide.
> Unfortunately, that will not work because the avaible equality tests in
> Oz (X==Y, cond X=Y ...) will generally suspend on unbound variables.
> 
> Is there some other way to do this? Or maybe an Oz primitive that I'm
> missing?
> 
> Put it more simply, is there any way in Oz to always tell whether to
> unbound variables are the same or not? I've been thinking of tricks
> involving spaces and stateful data, but I think it should be simpler
> than that.

I think {System.eq V1 V2 ?B} is what you are looking for...

Best,
Nils

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