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Subject: Re: [mercury-users] cc_multi vs det
From: Peter Ross (peter.ross@miscrit.be)
Date: Fri Dec 01 2000 - 21:26:58 EST
On Fri, Dec 01, 2000 at 10:07:09AM +1100, Tyson Dowd wrote:
> On 30-Nov-2000, Peter Ross <peter.ross@miscrit.be> wrote:
> > On Thu, Nov 30, 2000 at 04:08:25PM +1100, Mark Anthony BROWN wrote:
> > >
> > > Because there may have been more than one potential exception, and
> > > the Mercury implementation may have (operationally) chosen one of
> > > them. In code that handles exceptions, it is possible that different
> > > exceptions lead to different solutions, so the Mercury implementation
> > > may effectively be making a choice between two different solutions in
> > > the higher level predicate. This is (declaratively) modelled using
> > > committed choice nondeterminism.
> > >
> > I understand the declarative differences between cc_multi vs det.
> >
> > However I am not sure what effect these declarative differences have on
> > the generated code. Could someone give me an example of when the
> > distinction between cc_multi and det is important when the code is
> > generated (ie where having det instead of cc_multi leads to incorrect
> > code).
>
> The generated code is exactly the same.
>
> >From code_model.m in the compiler source:
>
> determinism_to_code_model(det, model_det).
> determinism_to_code_model(semidet, model_semi).
> determinism_to_code_model(nondet, model_non).
> determinism_to_code_model(multidet, model_non).
> determinism_to_code_model(cc_nondet, model_semi).
> determinism_to_code_model(cc_multidet, model_det).
> determinism_to_code_model(erroneous, model_det).
> determinism_to_code_model(failure, model_semi).
>
> cc_multi is the same code model as det.
> cc_nondet is the same code model as semidet.
>
> The correctness of the solutions will be the same, but there is a
> difference between a program which has `main' as det or cc_multi. A
> cc_multi program might behave differently (compute different solutions,
> and produce different IO as a result) even given the exact same starting
> conditions. A det program will not.
>
OK.
One of the problems with cc_multi is that it propogates quickly, which
can be a real pain.
Say I develop some code which is det. I then integrate this with some code
that is cc_multi, I must then propogate the cc_multi all the way up the
call chain, which is a real pain. So my question is, can not
propogating this information up the call chain ever lead to a situation
where the generated code is incorrect (ie the compiler does the wrong
thing currently, treating cc_multi code as det).
In other words is the cc_multi information only useful from a semantic
view point, but in practice doesn't really have much effect.
Pete
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