Re: [Sbcl-devel] found circular reading bug

[Brian M. <br...@ma...>]

On 4/1/07 7:15 PM, "David" <rsu...@sn...> wrote:

> Hi,
> 
> I'm using SBCL 1.0.2 and think I found a bug in the reader.  The
> following code returns NIL.  I believe it should return T.
> 
> (let ((foo (cons #1=(cons nil nil) #1#)))
>        (eq (car foo) (cdr foo)))
> 
> Can someone confirm this?

The behavior that SBCL exhibits is correct. To prove this to yourself, eval
a quoted version of the whole expression so you can see what it looks like
after the reader is done with it:

CL-USER(1): '(let ((foo (cons #1=(cons nil nil) #1#)))
       (eq (car foo) (cdr foo)))

(LET ((FOO (CONS (CONS NIL NIL) (CONS NIL NIL))))
  (EQ (CAR FOO) (CDR FOO)))

It's irrelevant that the code shares structure; the objects it produces do
not.

-- 
Brian Mastenbrook
br...@ma...
http://brian.mastenbrook.net