Matthew D Swank <akopa@...> writes:
> I cross posted since this list seems to have more activity.
It would probably have been redirected here, because at least I am not
about to give you a straightforward answer. :-/
> "You do not really understand something unless you can explain it to
> your grandmother." =E2=80=94 Albert Einstein.
While I think I probably could explain General Relativity to my
grandmother, unfortunately I can't explain the slot access of
Last time I was in the area, I confess that I cargo-culted enough so
that it seemed to work. We were implementing a hash value slot for
standard-instances and funcallable-standard-instances, and I think I
expressed my confusion thusly:
;;; FIXME: This seems to bear no relation at all to the CLOS-SLOTS
;;; slot in the FUNCALLABLE-INSTANCE structure, above, which
;;; (bizarrely) seems to be set to the NAME of the
;;; FUNCALLABLE-INSTANCE. At least, the index 1 seems to return the
;;; NAME, and the index 2 NIL. Weird. -- CSR, 2002-11-07
(defmacro fsc-instance-slots (fin)
`(%funcallable-instance-info ,fin 0))
I have also observed in the past that there's something odd going on
with CLOS/PCL discriminating functions, which don't allow themselves
to be overridden: see bug #343. This is likely related to some
weirdness happening in this area.
However, there _is_ a solution to your particular case. I don't
really recommend it; it's pretty horrible, but it comes about because
the lisp calling convention is different for
funcallable-standard-instances than it is for regular functions. If
> (defmacro promise (expr)
> (let ((instance (gensym)))
> `(let ((,instance (make-instance (quote promise)
> :expr (quote ,expr))))
> (delay ,expr))
(defmacro promise (expr)
(let ((instance (gensym)))
`(let ((,instance (make-instance 'promise :expr ',expr)))
#'(sb-kernel:instance-lambda () ,expr))
then I believe things start working.
Since I don't really know why things start working, I can't exactly
guarantee that these things will continue to work; I would love to be
told what is going on in this area. However, I hope this gets you
going, at least.