Re: print-circle and describe-variable

[Lennart Borgman (gmail)]

Chong Yidong wrote:
> "Lennart Borgman (gmail)" <address@hidden> writes:
>
> > Stefan Monnier wrote:
> > > > But we do believe that print-circle makes it possible to print out
> > > > recursive structures, or? And we do not believe that it disturbs printing
> > > > out non-recursive structures (except that it gets a bit slower), or?
> > > Actually, I believe it does affect printing non-circular structures in more
> > > ways than just by making it slower.
> > >
> > > Try (let ((print-circle t) (toto (list 2))) (prin1 (list toto toto)))
> > >
> > > In some cases, this is a good feature, but in many other cases it can be
> > > very confusing.
> >
> > Interesting, but is not that just another bug?
>
> Nope.  When print-circle is on, the printer takes note of shared
> substructures.  It's just that in this case, taking note of shared
> substructure obfuscates the value.

But the result I see is

  (#1=(2) #1#)((2) (2))

Why are the two printed representations of toto different? Hm. The doc 
is a bit unclear. To me it seems like

  #2=(#1=(2) #1#) #2

or

  (#1=(2) #1#) (#1=(2) #1#)

could both be possible. But not the one I actually see.

Yes (disregarding the output inconsistency above), I can see this is a 
difficulty. print-circle does not do exactly what I supposed. I believed 
it only jumped in when there were recursive structures (as the name 
suggests). Is there any function for checking if a structure is recursive?