[m-dev.] Suggestion for a new "where" operator

[Fergus Henderson]

On 07-Aug-2003, Peter Moulder <pmoulder at mail.csse.monash.edu.au> wrote:
> `q((X where p(X)), (X where p(X)))' has the same declarative semantics
> as `some[V] (V = (X where p(X)), q(V, V))' regardless of the number of
> elements in {X : p(X)}.
> 
>    p(X), p(X), q(X, X)              (duplicate-where version)

Well, it depends on what scoping rules we choose for "where" expressions.
I expected the scoping rules for `where' to be the same as if the code
had been written using `apply((func) = X :- p(X))' instead of `(X where p(X))'.
In that case, if there are no other occurrences of X outside the call
to q/2, then then two occurrences of X would be in different scopes, so
the semantics would be

	some [X] (p(X), V1 = X),
	some [X] (p(X), V2 = X),
	q(V1, V2)

which is different than the semantics for the single-where version.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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