Issue COPY-SYMBOL-COPY-PLIST Writeup

Issue:		COPY-SYMBOL-COPY-PLIST

References:	COPY-SYMBOL (p 169), COPY-LIST (p 268), COPY-TREE (p

		269).

Category:	CLARIFICATION

Edit history:	10-Jan-89, Version 1 by Margolin


Problem Description:


The description of COPY-SYMBOL, where the COPY-PROPS optional argument

is non-NIL, says that a copy of the property list is used as the new

symbol's property list.  However, there are several ways in which a list

may be copied, most notably COPY-LIST and COPY-TREE, and the description

doesn't say which mechanism should be used.


Proposal (COPY-SYMBOL-COPY-PLIST:COPY-LIST)


Clarify that when COPY-SYMBOL copies the property list of the symbol, it

is as if (COPY-LIST (SYMBOL-PLIST sym)) were used as the new symbol's

property list.


Rationale:


COPY-LIST is the simplest list-copying primitive.  The result of this

copy is that GET returns EQL results for the two symbols until one of

the property lists is altered, but altering either of the property lists

doesn't affect the other.  This is current practice in the

implementations I tested, and probably what most users assume.


Current Practice:


Symbolics Genera and Sun Common Lisp currently implement this.  I

suspect most others do, too.


Cost to Implementors:


Little or none.


Cost to Users:


None unless they've been assuming some other type of copy.


Benefits:


Less ambiguity.


Aesthetics:


Well, I like it.