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- To: (BUG LISP) at MIT-MC
- Subject: many DISPLACEs
- From: JONL at MIT-MC (Jon L White)
- Date: Fri, 16 Jun 78 07:41:00 GMT
- Original-date: 16 JUN 1978 0341-EDT
I'm perfectly happy with either the current definition of DISPLACE,
or with the one proposed by RMS, and am all in favor of "giving the
user what he wants". But before we go out to take a hasty vote,
it might be a good idea to examine all the consequences of the
more "totalitarian" choice. For example,
1) Should the functions be called "DISPLACE", since its action is
more of a macro-expansion shunting. Would the naive user be
aware that could not use "DISPLACE" for displacement, due to the
extra cruft pushed in.
2) Some macro-expansions take a monsterous amount of code, and produce
even more - the "DISPLACED" scheme saves both around, with no
choice available to the user, so that gc may be impacted. Admittedly
many users would like to be able to retrieve the source that the
expansion came from, but then again most wouldn't go to any effort
to save it. see 3.
3) The current definition is essentially the one that has been in the
LISP lore for the past 12 years, and one advantage of putting it
in the "system" is that it can become the SUBR that it rightly is
rather than hacking it in as another level of MACRO. Its persistent
use, in this form, would not seem to support the statement "Putting
in any other sort of DISPLACE [than SDISPLACE] is tantamount to not
putting in any, but creating some random system function instead."
4) My suggestion of a standard MACRO libaray, which would supply
SDISPLACE (or better yet, MACRO-DISPLACE), doesn't seem to require
that "each user must define it himself". Or at least I didn't
think so. Anyway, there are probably hordes of users who wont displace
anything, but will be content with ordinary macro expansion. How
dull! But if I read the most recent rmsuggestion correctly, we would
have to require everyone to use the new "SDISPLACE" form of macros
in order for automatic code analysis programs to have any success.
Hence the appellation "totalitarian".