[racket-dev] Optional equality predicate for assoc and member

About a minute ago, Robby Findler wrote:
> On Sun, Apr 24, 2011 at 7:53 PM, Eli Barzilay <eli at barzilay.org> wrote:
> > Here's another idea: in a world of immutable lists there are *much*
> > less circular lists.  (Even more: the fact that they're generated via
> > a temporary structure that is then copied means that they're usually
> > very short too.)  Maybe it's fine to take it to the next level and
> > just have all the standard functions ignore cycles?  Possibly with
> > alternative names (or a new module) for versions that do account for
> > cycles -- therefore putting the burden on the rare uses of circular
> > lists?
> 
> How about, instead of that: keep a counter and when you've seen 1000
> (or 10000) cons cells or some other large number, then switch into a
> safe mode?

But that means that there's still an extra variable to keep around,
which is the main penalty with the tortoise pointer, right?  (The
other part being the almost inevitable code repeatage...)

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!