Re: DEFSTRUCT copier query

[Pavel.pa@Xerox.COM]

    Date: Mon, 3 Nov 86 10:54 EST
    From: Rob MacLachlan <RAM@C.CS.CMU.EDU>

        Date: Monday, 3 November 1986  10:17-EST
        From: <samalone at ATHENA.MIT.EDU>

        (copy-bread (make-rye-bread :state 'stale :seeded-p nil))

             A:	#S(RYE-BREAD :STATE STALE :SEEDED-P NIL)
        or
             B:	#S(BREAD :STATE STALE)

    Since there doesn't seem to be any support for B, no one can
    complain if you implement A, although it may not be required for
    Common Lisp.

I can complain, and I would.  I am strongly of the opinion that the
function COPY-BREAD here should always create a value of type BREAD, not
one of its subtypes.  If you want to get the effect of A, let us create
a new function COPY that copies any Lisp value at all.  It seems strange
to have several such functions, one for each section of the type space.
I claim that such a function, along with COPY-BREAD having semantics B
above, would provide all of the functionality desired in the cleanest
way.

	Pavel