[m-rev.] for review: new mdb commands "hold" and "diff"

[Julien Fischer]

On Mon, 11 Jul 2005, Zoltan Somogyi wrote:

> On 11-Jul-2005, Julien Fischer <juliensf at cs.mu.OZ.AU> wrote:
> > > + at item held variables
> > > + at cindex held variables (in mdb)
> > > +Normally, the only variables from the program accessible in the debugger
> > > +are the variables in the current environment at the current program point.
> > > +However, the user can @emph{hold} variables,
> > > +causing their values -or selected parts of their values-
> > > +to stay available for the rest of the debugger session.
> >
> > I suggest also mentioning that held variables also maintain their
> > values with respect to retries.
>
> If they are ground and created ground (i.e. not created as a skeleton and
> later filled in), they will. If they are solver variables that reference
> a changing constraint store, then their internal view may stay the same,
> but the external one won't. I don't want to make a promise I can't keep.
>
I think the documentation should mention this then.

> > > + at item hold @var{name}[@var{termpath}] [@var{heldname}]
> > > + at kindex hold (mdb command)
> > > +Holds on to the variable @var{name} of the current event,
> > > +or the part of the specified by @var{termpath},
> > > +even after execution leaves the current event.
> > > +The held value will stay accessible via the name @var{$heldname}.
> > > +If @var{heldname} is not specified, it defaults to @var{name}.
> >
> > What happens if heldname is reused, or is that not allowed?
>
> It's not allowed.
>
> It wouldn't be too hard to add new commands for renaming and/or deleting
> held variables, but let's see whether there is any need for them.
>

I'm not arguing for or against the facility; I just think the
documentation should say that it is not (currently) allowed.

Julien.
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