[m-dev.] For review: declarative debugging back end (3/3)

[Fergus Henderson]

On 16-Jul-1998, Mark Anthony BROWN <dougl at cs.mu.OZ.AU> wrote:
>
> Even better, I could replace the last sentence of the comment by:
> 
> 	In particular, this allows a module to represent data the same
> 	way inside atoms as out.  This is quicker and more compact than
> 	using a uniform representation, because no conversion is required
> 	while building the EDT.

That would be fine.

> I could describe
> the overall scene in something like compiler/notes/compiler_design.html
> and make references to it from here.  Or, when a front end is written
> I can point to it as an example of use.

> > > 	%
> > > 	% For missing answer analysis also, the goal justification is a
> > > 	% tree that corresponds to the structure of the program.  It is
> > > 	% the dual of the above structure: it represents which atoms
> > > 	% were _not_ computed answers.
> > > 	%
> > > 	
> > > :- type miss_tree(A)
> > > 	--->	local_call(evaluation_tree(A))
> > > %	;	some [E] external_call(evaluation_tree(E))
> > > %			<= evaluation_atom(E)
> > > 	;	conj(list(miss_tree(A)))
> > 
> > Shouldn't that be `conj(int)'?
> 
> I don't think so.  In Lee's declarative debugging scheme, the children
> of an `mp' node include `mp' nodes for each conjunct.  A miss_tree
> holds the children of (the Mercury equivalent of) an `mp' node.

If a conjunction has a missing answer, it is not necessarily
the case that all conjuncts will have a missing answer;
only one conjunct need have a missing answer.

I thought miss_trees represented missing answers.
Is that not always the case? 

(What does a `trivial' miss_tree mean?)

> Was my reference to it being a dual structure confusing?

Yes...

> I could
> change it to something like "Its purpose is the dual of the above
> structure's purpose..."

I suppose that would help.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3        |     -- the last words of T. S. Garp.