[m-rev.] for review: where safe_equality is ...

[Fergus Henderson]

On 13-May-2003, Zoltan Somogyi <zs at cs.mu.OZ.AU> wrote:
> On 13-May-2003, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > I don't understand the rationale for this change.
> > If the hand-defined types are being replaced with foreign types,
> > it should be impossible to write a unification which examines
> > their representation, so no unifications of values of those
> > types should be required to be in committed choice contexts.
> > 
> > Could you give an example of a type for which `safe_equality'
> > would be necessary?
> 
> The thing that prompted me to do this change is that I changed type_desc
> and type_ctor_desc in type_desc.m to foreign types. I then got a bunch of
> errors in std_util, which contains
> 
> :- type type_desc == type_desc__type_desc.
> :- type type_ctor_desc == type_desc__type_ctor_desc.
> 
> The automatically created unify preds for these types got errors
> because the calls to the unify preds of the underlying types weren't
> in committed choice contexts.

That sounds like a bug.  It shouldn't report an error for that.
The (in, in) mode of unification has determinism `semidet',
not `cc_multi', and so it should be fine to call it from a non-cc context.

-- 
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.
--------------------------------------------------------------------------
mercury-reviews mailing list
post:  mercury-reviews at cs.mu.oz.au
administrative address: owner-mercury-reviews at cs.mu.oz.au
unsubscribe: Address: mercury-reviews-request at cs.mu.oz.au Message: unsubscribe
subscribe:   Address: mercury-reviews-request at cs.mu.oz.au Message: subscribe
--------------------------------------------------------------------------