[m-rev.] for review: fix singleton variable warning problem

[Fergus Henderson]

On 31-May-2002, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> 
> This is still treating the symptom, not the cause. Why do variables
> in foreign_proc clauses need to be handled differently? Why doesn't
> this problem occur with Mercury clauses?

The problem doesn't occur with Mercury clauses because after flattening
(conversion to SHF), the head variables in Mercury clauses are never
singletons; the head variables are always "HeadVar__N", which might
get unified with singleton variables in the body, but which are not
themselves singletons.

For foreign_proc clauses, we don't use "HeadVar__N" as the head variables;
instead, we use the variables that the user specified directly.

One possible solution, then, might be to change the way we handle
foreign_proc clauses, so that we do introduce "HeadVar__N" variables
and the corresponding unifications for those.  I don't know if that
would be a good idea, or if it might result in other problems...

-- 
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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