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

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?

Mode analysis would be a nice thing to have ...

	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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