The cycle detection for a tree would probably look something like,
SCM scm_equal_cons(SCM x, SCM y, SCM slow, int move)
{
SCM res;
if(scm_is_pair? (x) && scm_is_pair (y))
{
if(scm_is_eq (x, slow)) cycle_detection_hit();
if(move)
if(scm_is_pair? (SCM_CAR (slow)))
slow = scm_cons(SCM_CAAR (slow),
scm_cons(SCM_CDAR (slow), SCM_CDR (slow)));
else
slow = SCM_CDR (slow);
ccccccccccccccx
res = scm_equal_cons (SCM_CAR(x), SCM_CAR(y), slow, !move);
if(scm_is_false (res)) return SCM_BOOL_T;
res = scm_equal_cons (SCM_CDR (x), SCM_CDR (y), slow, !move);
}
}
Although it probably works there will be a lot of consing being done
slowing the algorithm, as said.
So I take back what I said earlier with tree cycle code added equal will be
slower.
/Stefan
On Sun, Sep 2, 2012 at 5:17 PM, David A. Wheeler <dwhee...@dwheeler.com>wrote:
> I said:
> > > I'd really like for there to be a common spec for Scheme with
> libraries, etc., and my hope is that R7RS will be that spec.
>
> Ian Price:
> > Call me a cynic, but if r6rs couldn't do that, then I don't see how r7rs
> > could be given that it actively avoids many important portability
> questions.
>
> Well, the cynics are often right :-). But I think R7RS is intentionally
> much more conservative and R5RS-like. In particular, it's *supposed* to be
> easy for an R5RS implementation to move to R7RS. If it's easier to adopt,
> it's more likely to be adopted.
>
> Scheme is rediculously non-portable due to its lack of a *standard*
> library system. If a standard for *that* could be widely adopted, many
> other portability problems would be drastically reduced.
>
> > But we all can dream...
>
> Indeed!
>
> --- David A. Wheeler
>
>
