[m-dev.] For review: new DD front end architecture

[Mark Anthony BROWN]

Peter Schachte writes:
> 
> On Tue, Dec 07, 1999 at 02:25:10AM +1100, Mark Anthony BROWN wrote:
> > Implement the new architecture for the front end of the
> > declarative debugger.  Disable declarative debugging if conservative
> > GC is not being used since this change relies on it.
> 
> It's a bit disappointing not to be able to use the declarative
> debugger in no-gc modes.  In what way to you rely on gc?  When the
> accurate (gee, shouldn't it be called "precise"?) garbage collector is
> available, will declarative debugging be possible in agc modes?
> 

Yes, it would be convenient to be able to declaratively debug programs
without having to recompile in a suitable grade.  But in practice
the non-GC grades are less useful than you might think, since even
small examples run out of memory :(.  To remove the reliance on GC
I would need to copy all data constructed in the browser onto the
global heap, along with any program data that may be reclaimed
due to backtracking.  This is not too hard, but is still not worth
the effort, IMHO, since there is little to be gained.

OTOH, the declarative debugger should be able to benefit a lot from agc.
Tyson and I discussed this yesterday, and we concluded that it
would be well worth supporting DD in agc grades in future.  However,
I won't implement this support until I understand more about the
memory requirements of DD, and about how agc works.  I'd like to get
a stable debugger working in some grade before trying to optimize
its performance ;).

Cheers,
Mark.
-- 
Mark Brown, PhD student            )O+  |  "Another of Fortran's breakthroughs
(m.brown at cs.mu.oz.au)                   |  was the GOTO statement, which was...
Dept. of Computer Science and Software  |  uniquely simple and understandable"
Engineering, University of Melbourne    |              -- IEEE, 1994
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