Subject: Re: Cons Cell Representation---`sameness' again
From: Erik Naggum <>
Date: 1999/04/08
Newsgroups: comp.lang.lisp
Message-ID: <>

* Barry Margolin <>
| You've never heard of a machine-level debugger?  Get yourself a Lisp
| Machine and type (si:ddt).  I also recall low-level functions that would
| return the address that a locative refers to, as an integer.

  yes, of course I have heard of them, I just find it wholly irrelevant to
  a discussion of object sameness, which I tried really hard to show with
  the virtual memory page example, which goes below visible machine address
  to physical machine address.

| Or if you have a foreign function interface, the foreign language may be
| able to convert the address of a Lisp object that you pass to an integer,
| and return that integer.

  yep, that's the violation of the sanity of the system.

| This is what was meant by a machine-level microscope.  It's operating
| below the level of the Lisp language, looking at the hardware
| representations.

  but, but, this microscope has memory and shows you what was before in a
  way that is entirely artificial.  I mean, copying GC is just like paging
  the same data in at a different physical memory location.

  in effect, this "argument" drops an important context: instead of saying
  "the bit strings" it should say "the bit strings at time T1" and "the bit
  strings at time T2".  but that would make the silliness explicit...

| I agree that this is not really a very useful level to mention in this
| thread.

  whew!  :)