Re: member and findall or setof don't get along? [Solved]

On Tue, 2014-04-15 at 09:07 +0200, Jan Wielemaker wrote:
> On 15-04-14 08:52, Ross Boylan wrote:
> > The following fails on the first recursion at the findall:
> > cd1([Disk | Ds], SoFar, Names, WithDates) :-
> > 	format("Ancestor Graph ~p: ", Disk),
> > 	deep_ancestors(Disk, now, Graph),
> > 	format(atom(FileName), "ancestors-~p.svg", [Disk]),
> > 	u_plot(Graph, FileName),
> > 	pgraph(Graph, WithDates), nl, nl,
> > 	vertices(Graph, Vs),
> > 	%setof(Name, W^member(nw(Name, W), Vs), Names),
> > 	findall(Name, member(Name, Vs), Names),
> > 	append(SoFar, Names, SoFar2),
> > 	cd1(Ds, SoFar2, Names, WithDates).
> 
> On the second iteration, Names is already bound, so setof/findall
> only succeeds if the result set is exactly the same as for the first
> iteration.  That is probably not what you want.  Maybe findall/4?
Thank you.  Names should be 2 separate variables:
cd1([Disk | Ds], SoFar, Names, WithDates) :-
	format("Ancestor Graph ~p: ", Disk),
	deep_ancestors(Disk, now, Graph),
	format(atom(FileName), "ancestors-~p.svg", [Disk]),
	u_plot(Graph, FileName),
	pgraph(Graph, WithDates), nl, nl,
	vertices(Graph, Vs),
	setof(Name, W^member(nw(Name, W), Vs), VNames),
	append(SoFar, VNames, SoFar2),
	cd1(Ds, SoFar2, Names, WithDates).

I had combined the code from 2 predicates into cd1, resulting in the
"name" clash.

> 
> Mode analysis would be a nice thing to have ...
I'm guessing that means telling whether variables are + or -.
Ross
> 
> 	Cheers --- Jan
> 
> > It also failed with the setof.  So on the first call it works; then it
> > recurses and fails.  In the debugger it simply fails immediately at the
> > line, even if I try to step in.  But see below for a variant in which it
> > succeeds only if stepped into with the debugger.
> > 
> > When I try to reproduce with a small example, using the value of Vs
> > showing in the debugger just before the failure, everything works:
> > weird(Names) :-
> > 	Vs = [ nw(littleboy,now),
> > 	       nw(pdb,now),
> > 	       nw(pdb5,now),
> > 	       nw(dpath([lv(backup,littleboy)]),now),
> > 	       nw(path([oscorn1, usr, local, var, spool, bacula]),now),
> > 	       nw(lv(backup,littleboy),now)
> > 	     ],
> > 	setof(Name, W^member(nw(Name, W), Vs), Names).
> > 
> > Also, using
> > 	setof(Name, cd1a(Vs, Name), Names),
> > 
> > with the helper
> > cd1a(Vs, Name) :-
> > 	member(nw(Name, _), Vs).
> > 
> > fails at the same spot if I step over ('s') setof.  But if I trace into
> > it (' '), the entire operation succeeds.  Then the next u_plot fails.
> > 
> > commenting out u_plot and pgraph did not help.  Vs is not empty and
> > consists entirely of nw(_,_) items according to the debugger.
> > 
> > Running 6.4.1.
> > 
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