defvar, defparameter, :unbound

[Guy Steele <gls@THINK-AQUINAS.ARPA>]

    Date: Mon,  4 Nov 85 23:18:59 EST
    From: "Glenn S. Burke" <GSB@MIT-MC.ARPA>

	From: Daniel L. Weinreb <DLW@SCRC-QUABBIN.ARPA>
	    Date: Sat, 2 Nov 85 23:55:45 EST
	    From: Nick Papadakis <isrlist@tove.umd.edu>

	    On the lispmachines, defvar will take a second argument of :unbound,
	    meaning that the variable will be initialized to an unbound state.

	I'm not sure which Lisp machine this message is supposed to apply to,
	but just for the record, the Symbolics system does not do this.

    This hack was added to NIL.  My personal feeling is that the special
    case value is just asking to screw some poor user whose code just
    happens to naively use :UNBOUND to mean something...   But i added the
    defvar hack anyway, because the ability to do both the defvar and
    specify the documentations string in a single form seemed worth it.
    Doing
	    (defvar *foo*)
	    (setf (documentation '*foo* 'variable) "Documentaiton string")
    looks pretty crufty.  Keyworded defvar, anyone?

One idea that was discussed previously was
	(defvar *foo* *foo* "Documentation string")
which self-evidently means "declare *foo* and initialize to its existing
value", but by special dispensation it arranges to work even when *foo*
is already unbound, i.e., it leaves it alone.  This is fine for DEFVAR,
but is less appealing for DEFPARAMETER.
--Guy