Portability of ` usage

[lgm@ihlpf.att.com]

Our application uses  `   to construct keyword argument lists
(i.e., property lists) which are then passed around, stored in
data structures, etc.  I am concerned about the statement in CLtL
that "...no guarantees are made as to whether the constructed copy
of the template will or will not share list structure with the
template itself."  Does this mean that an implementation could
conceivably rig a  `  expression to return the same list structure
on each execution, destructively modifying the structure for each
use of  , ?  For example, consider a function

	(DEFUN IN-LIST (ARG) `(,ARG))

Is it really permissible for a Common Lisp implementation to
return the same (according to EQL) value for these two calls?

	(IN-LIST 3)

	(IN-LIST 4)

Symbolics' implementation doesn't do this, of course, but if the
standard considers it permissible, we may have to modify our usage
to ensure portability.


	Lawrence G. Mayka
	AT&T Bell Laboratories
	lgm@ihlpf.att.com

Standard disclaimer.