Do symbols need to be EQ?

[Kenneth Tilton]

On Fri, Jul 3, 2015 at 4:48 AM, Edi Weitz <edi at weitz.de> wrote:

> Perhaps the excerpt below (from a fresh LW image) makes more obvious
> what my "philosophical problem" is.  I have redacted the output of
> DISASSEMBLE to only show the relevant parts.  It shows that EQ is
> essentially just one simple comparison with a machine word (which is
> what I expected).  It also shows that I get the same machine word
> again as long as I don't mess around with UINTERN or something.  But
> once I've done that, I get _another_ machine word and so in terms of
> simple-minded EQ I get a different object.
>
> CL-USER 1 > (defun foo-1 (x)
>               (eq x 'bar))
> FOO-1
> CL-USER 2 > (disassemble 'foo-1)
>       ;; ...
>       21:      3DF771F921       cmp   eax, 21F971F7    ; BAR
>       26:      750D             jne   L3
>       ;; ...
> NIL
> CL-USER 3 > (defun foo-2 (x)
>               (eq x 'bar))
> FOO-2
> CL-USER 4 > (disassemble 'foo-2)
>       ;; ...
>       21:      3DF771F921       cmp   eax, 21F971F7    ; BAR
>       26:      750D             jne   L3
>       ;; ...
> NIL
> CL-USER 5 > (unintern 'bar)
> T
> CL-USER 6 > (defun foo-3 (x)
>               (eq x 'bar))
> FOO-3
> CL-USER 7 > (disassemble 'foo-3)
>       ;; ...
>       21:      3DAB71F921       cmp   eax, 21F971AB    ; BAR
>       26:      750D             jne   L3
>       ;; ...
> NIL
>
>
Sorry, where is the problem? The spec is clear that a new object (with a
new pointer) will be created given the unintern hijinx, so all is
consistent: different pointer, EQ->nil.

ie, It is not just "in terms of EQ" that you have a different object: you
have created two distinct pointer objects (and EQ dutifully says so).

And at a higher level of abstraction, you have created two different
symbols, one interned and one not.

-kt

-- 
Kenneth Tilton
54 Isle of Venice Dr
Fort Lauderdale, FL 33301

ken at tiltontec.com
http://tiltontec.com
@tiltonsalgebra

646-269-1077

"In a class by itself." *-Macworld*
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.common-lisp.net/pipermail/pro/attachments/20150703/d9ff0b0d/attachment-0001.html>