[m-rev.] diff: handle user defined equality in rtti_implementation__deconstruct

[Fergus Henderson]

On 29-Nov-2002, Peter Ross <pro at missioncriticalit.com> wrote:
> fjh wrote:
> > On 29-Nov-2002, Peter Ross <pro at missioncriticalit.com> wrote:
> > > +handle_usereq_type(Term, TypeInfo, TypeCtorInfo,
> > > + TypeCtorRep, NonCanon, Functor, Arity, Arguments) :-
> > > + ( NonCanon = do_not_allow,
> > > + error("attempt to deconstruct noncanonical term")
> > > + ; NonCanon = canonicalize,
> > > + Functor = expand_type_name(TypeCtorInfo, yes),
> > > + Arity = 0,
> > > + Arguments = []
> >
> > The two lines above look wrong -- there should at least be an XXX comment
> > there.
> >
>         case MR_TYPECTOR_REP_ENUM_USEREQ:
>             if (noncanon == MR_NONCANON_ABORT) {
>                 /* XXX should throw an exception */
>                 MR_fatal_error(MR_STRINGIFY(EXPAND_FUNCTION_NAME)
>                     ": attempt to deconstruct noncanonical term");
>                 break;
>             } else if (noncanon == MR_NONCANON_ALLOW) {
>                 handle_noncanonical_name(type_ctor_info);
>                 handle_zero_arity_args();
>                 break;
>             }
>             /* else fall through */
> 
>         case MR_TYPECTOR_REP_ENUM:
>             handle_functor_name(MR_type_ctor_layout(type_ctor_info).
>                     MR_layout_enum[*data_word_ptr]->MR_enum_functor_name);
>             handle_zero_arity_args();
>             break;
> 
> Here is the C code from mercury_ml_expand_body.  As you can see in
> MR_NONCANON_ALLOW case, we expand the type name and return 0 arity.
> Consequently the Arguments should be the empty list.

For enums, fine -- all values of enumeration types are constants
and thus have zero arity.

But the procedure you are defining here doesn't say anything in its
name about only being valid for enums, and in your code it gets called
for du types, not just enum types.

-- 
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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