Re: Mysteries of unwind-protect

On 15 Jan 2026, at 21:26, Michał phoe Herda <[email protected]> wrote:
> 
> I'd assume the lexical variable access cannot be optimized away in order to allow you to SETF V in the debugger like you did above. What's your DEBUG setting and does this whole issue also manifest with DEBUG 0?

It was whatever the ambient value was.  But interestingly both LW and SBCL still complain with debug 0.  And SBCL complains not where I would expect it to.  Given this:

(defun ts/nodebug (n)
  (declare (type fixnum n))
  (declare (optimize speed (debug 0) (safety 0))) ;safety tried as well
  #+LispWorks
  (declare (optimize (float 0))
           (:explain :boxing))
  (let ((v (make-array 1 :element-type 'double-float :initial-element 0.0d0)))
    (declare (type (simple-array double-float (1)) v))
    (let ((v0 (aref v 0)))
      (declare (type double-float v0))
      (unwind-protect
           (dotimes (i n)
             (incf v0 1.0d0))
        (setf (aref v 0) v0))))
  (values))

Then it will complain about the INCF, and experimentally it conses furiously.  That's not really a problem for this list though.

And with the above, LW now doesn't complain at all (and doesn't cons), so now I am really confused.

I think the answer is that unwind-protect is something you don't want to use unless you need to.  Which was what I already thought, so that's good.

--tim





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