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From: klapper@oravax.UUCP (Carl Klapper)
Newsgroups: comp.lang.lisp
Subject: Re: FALSE vs empty list
Summary: lisp booleans are just plain weird
Message-ID: <1646@oravax.UUCP>
Date: 7 Sep 90 15:57:52 GMT
References: <24305@uflorida.cis.ufl.EDU> <1350029@otter.hpl.hp.com>
Organization: Odyssey Research Associates, Ithaca NY
Lines: 42

In article <1350029@otter.hpl.hp.com>, sfk@otter.hpl.hp.com (Steve Knight) writes:
> If you are happy applying boolean operators to lists and list operators to
> booleans, then you will have little inclination to change.  You may even
> enjoy the conciseness of idioms such as
>     (car (or (member x L1) (member x L2) '(())))
> which exploit the conflation of lists and booleans.

or even ...

  (defvar list-where-found nil)

  (defun member-note-list (x l)
    (let ((member-list (member x l)))
      (when member-list
	    (setq list-where-found l)
	    member-list)))

   (setf (car (or (member-note-list x L1)
                  (member-note-list x L2)
		  '(())))
	 list-where-found)

   (and (member-note-list x L3) (member-not-list x list-where-found))

which exploit the execution sequences of OR and AND.

Clearly, lisp booleans and boolean operators diverge from mathematical
booleans and boolean operators.

BTW, my preferences for TRUE and FALSE are :

	TRUE 		#s(AND :ARGS NIL)
	FALSE		#s(OR :ARGS NIL)

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