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The T and NIL issues (and etc.)
- To: moon at SCRC-TENEX
- Subject: The T and NIL issues (and etc.)
- From: Jon L White <JONL at MIT-MC>
- Date: Mon, 15 Mar 1982 01:31:00 -0000
- Cc: common-lisp at SU-AI
The msg of following dateline certainly describes well the status
quo in MacLISP (both PDP10 and LISPM), as well pointing out the
T is special-cased in CASE clauses.
Date: Sunday, 14 March 1982 14:40-EST
From: Symbolics Technical Staff
To: Common-Lisp at SU-AI
Subject: The T and NIL issues
. . .
But as EAK says, there is no reasoning given, beyond the authors'
personal preference, for retaining the "wart" of NIL = ().
One comment from that msg deserves special attention:
T and NIL are just like the hundreds of other reserved words in Lisp,
dozens of which are reserved as variables, most of the rest as functions.
. . .
Why should even dozens of user-visible variables be reserved? This is one
of the strongest complaints against LISP heard around some MIT quarters --
that it has become too hairy, and the presence of the LISPManual doesn't
help any. And again, even if there be many "reserved" names for functions,
the separabililty of function-cell/value-cell makes this irrelevant to the
Perhaps the package system could "hide" more of the systemic
function/variables, but why should it come up now? The notion of
lexically-scoped variables, as mentioned in my note
Date: 5 March 1982 12:09-EST
From: Jon L White <JONL at MIT-MC>
Subject: How useful will a liberated T and NIL be?
To: Hedrick at RUTGERS
indicates that the variable T (and indeed NIL too) can be fully useful,
even if its global value serves in its present "status quo" capacity.
(DEFUN FOO (PRED F T)
(DECLARE (LOCAL F T))
(COND (F (NULL PRED))
(#T () )))
the local declaration will totally isolate "T" from the effects of any