[racket] iterative lazy space-safe or not?

20 minutes ago, Keiko Nakata wrote:
> Hi,
> 
> In the post-finalization discussion on iterative lazy algorithms (SRFI 45),
> (http://srfi.schemers.org/srfi-45/post-mail-archive/msg00024.html)
> Andre van Tonder points that Eli's proposal, 
> which I think is used in Racket roughly, is not memory safe.
> But I do not get his point.
> 
> (force (letrec ([x1 (lazy x2)] [x2 (lazy x3)] [x3 (lazy 4)]) x1))
> 
> ends up with a graph in which x1 points to 4 and both x2 and x3
> point to x1.  Am I correct?

Yes.


> And indeed I do not get out-of-memory for 
> 
> (define (g x) (lazy (begin (garbage-collect) (g x))))
> 
> Is the problem mentioned in the discussion specific to stream
> implementation?  Or, am I missing something?

I don't remember the details exactly, but I think that there was some
other bug at the time.

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