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- To: HIC at MIT-MC
- From: GLS at MIT-MC (Guy L. Steele, Jr.)
- Date: Tue, 27 Jun 78 18:09:00 GMT
- Cc: (BUG LISP) at MIT-MC, (BUG LISPM) at MIT-MC
- Original-date: 27 JUN 1978 1409-EDT
More generally, the suggestion should be that ATOM be used in
preference to NULL in most functions that traverse lists. This should
probably be true in most NIL implementations, as a mater of error-checking
if nothing else. On the PDP-10 NULL tests are cheaper than ATOM tests.
Even in NIL there is the question of whether we want to *define*
LENGTH, LAST, etc. to use ATOM tests (which would permit the loser to depend
on it), against the possibility that on some NIL implementation
a NULL test might be significantly faster than an ATOM check.
I would lean toward indeed so defining them to use ATOM, but
want to raise that issue.