[m-rev.] for review: make each SCC a set

[Paul Bone]

On Mon, Feb 20, 2017 at 04:10:11PM +1100, Zoltan Somogyi wrote:
> 
> 
> On Mon, 20 Feb 2017 16:03:59 +1100, Paul Bone <paul at bone.id.au> wrote:
> > > Names like return_bottom_up_sccs and return_top_down_sccs would work
> > > only if for each edge x->y, it were obvious which of x and y is higher.
> > > For our use case, this is clear, but for other use cases, it could be clear
> > > the other way around. Any ideas for better names? All I came up with
> > > are return_sccs_in_from_to_order and return_sccs_in_to_from_order,
> > > relying on the fact that it is pretty clear that x is "from" and y is "to",
> > > but those names are not exactly catchy.
> > 
> > I think these are the best names we can find,
> 
> Which "these" are you referring to? The top_down/bottom_up pair,
> or the from_to_order/to_from_order pair?

top_down/bottup_up

caller_callee_order/caller_callee_order is longer, but I understand it
straight away.

> > but I still have to remind
> > myself what they mean.  In other words I have to remind myself that parents
> > are drawn above children and/or that callers are parents, and callees are
> > children. 
> 
> Edges in digraphs can be used to represent many relationships other than
> parent/child relationships, and those relationships don't necessarily have
> anything to do with up vs down, which is why I don't see the top_down/bottom_up
> names as being a good choice.

Yes, this is the problem where you generalise something to a mathematical
concept (graphs) and the general language becomes less intuitive.  This is
probably why I have to think for a moment about what up and down are.

> > I think this is something I confuse myself about sometimes but
> > maybe others do as well.
> > 
> > But comments like this help:
> > 
> >     make_dependency_info(Graph) = dependency_info(Graph, BottomUpOrdering) :-
> >         % digraph.atsort puts the cliques of parents before the cliques
> >         % of their children. This is a top down order.
> >         digraph.atsort(Graph, TopDownOrdering),
> >         list.reverse(TopDownOrdering, BottomUpOrdering).
> 
> Thanks.
> 
> > I suggest a little reminder in a comment on the declrations for these
> > functions/predicates.
> 
> This diff already added some.
> 

Sorry, I didn't notice.


-- 
Paul Bone
http://paul.bone.id.au