Subject: Re: Car and cdr (Re: Python syntax in Lisp and Scheme)
From: rpw3@rpw3.org (Rob Warnock)
Date: Tue, 21 Oct 2003 01:52:07 -0500
Newsgroups: comp.lang.python,comp.lang.lisp
Message-ID: <btCdnXAhTbAKSgmiXTWc-w@speakeasy.net>
Christos "TZOTZIOY" Georgiou  <tzot@sil-tec.gr> wrote:
+---------------
| AFAIK car stands for contents of address register and
| cdr for contents of contents of data register.
+---------------

From the IBM 704 CPU instruction format:
CAR == "Contents of Address [part of] Register".
CDR == "Contents of Decrement [part of] Register".
See <URL:http://www.catb.org/~esr/jargon/html/C/cdr.html>.

Note that the PDP-10 AOBJP/AOBJN/BLKI/BLKO/PUSH/PUSHJ/POP/POPJ
instructions used a similar format, but with the "decrement" part
being a negative count in the upper half of the word (which was
*incremented* in parallel with the address in the lower half
[or in the case of POP & POPJ only, decremented in parallel with
the address]).


-Rob

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