[m-rev.] for review: make deconstruct work for herbrand variables

[David Jeffery]

On 10-Jul-2001, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> >                      case MR_SECTAG_VARIABLE:
> > -                        MR_fatal_error(MR_STRINGIFY(EXPAND_FUNCTION_NAME)
> > -                            ": cannot expand variable");
> > +                        handle_functor_name("<<variable>>");
> > +                        handle_zero_arity_args();
> > +                        return;
> 
> You should add `expand_info->non_canonical_type = TRUE;'
> at the start of the case.  Because deconstructing a term
> whose inst is unknown and and figuring out whether it is
> ground or not should definitely be cc_multi rather than det.
> 
> Oh wait, that will break the debugger gain, since we don't have
> variants of deconstruct (etc.) that allow this.  We should add
> such variants, and fix the debugger to call them.
> 
> In the mean time, add it, but leave it commented out.
> (Preferably with a comment explaining why.)

I have added the following comment:

                                /*
                                ** XXX We should do something like the
                                ** following, since deconstructing a value
                                ** that might be a variable should be
                                ** cc_multi rather than det. However, there
                                ** is no such version of deconstruct yet,
                                ** so we'll leave it out.
                                */
                        /*expand_info->non_canonical_type = TRUE;*/

> The "return;" statement there, buried in the middle of a very long function,
> is asking for trouble.

You are right, but in this case I thought it was less of an evil than trying
to escape gracefully from the nested switch.


dgj
-- 
David Jeffery (dgj at cs.mu.oz.au) | If you want to build a ship, don't drum up 
PhD student,                    | people together to collect wood or assign 
Dept. of Comp. Sci. & Soft. Eng.| them tasks and work, but rather teach them 
The University of Melbourne     | to long for the endless immensity of the sea.
Australia                       | -- Antoine de Saint Exupery
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