Faré wrote:

Indeed, (delete ...) has side-effects and doesn't preserve its second argument.

Although I can hardly imagine any implementation where DELETE on lists would operate in ways that break the code (except for an ANSI-compliance stress tester mode), it's not correct use of DELETE by the CLHS.

Thus, a minimally disruptive patch would be to replace

(delete entry index) with (setf index (delete entry index)) twice,

Funny. It seems the code has an extra element in the list precisely to avoid the well-known "delete yields empty list not reflected in variable" Lisp FAQ issue, but CLHS precisely disables such optimization when using DELETE (instead of a self-written naive implementation).

Someone who understands the code better audit what is being done by the considered functions.

and (delete nil temps) with (remove nil temps).

Assuming you're talking about make-mv-dsetqs: (let ((mv-setq `(multiple-value-setq ,vars ,value)) (temp-vars (delete nil temps))) Great, that's not just being picky about standard compliance, you discovered a real bug in the code! temps is still used afterwards and DELETE destroys it. REMOVE MUST be used instead.

Here's a testcase I came up with: (let (x y z) (dsetq (values nil x (y z)) (values 1 'a '(b c))) (list x y z)) must yield (a b c), not (a nil nil).

Regards, Jörg Höhle.