Package = map from symbol name to symbol object.
INTERN ~= (or (gethash ...) (setf (gethash ...)))
UNINTERN ~= remhash

There's nothing special about symbols. You'd get the same effect with a map of constants and operations to add/remove them from the map.

On Fri, Jul 3, 2015 at 10:56 AM, Kenneth Tilton <ken@tiltontec.com> wrote:


On Fri, Jul 3, 2015 at 4:48 AM, Edi Weitz <edi@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

@tiltonsalgebra


"In a class by itself." -Macworld