setf not working

[Didier Verna]

  Hello,

yesterday, I fell on something extremely weird, or at least, which I
currently fail to understand. Basically, after a (defvar *var*), there
are times when (setq *var* '(0 0)) doesn't work (the previous value of
*var* remains in effect).

I cannot currently provide a minimal example because the situation
involves several levels of nested macro / function calls in code I
didn't write (*var* is solely mine though).

At first, I thought I had fallen on a compiler bug, but I get the same
behavior with at least 3 lisp implementations.

I ultimately found a workaround, consisting in using (list 0 0) instead
of '(0 0) in the assignment. I'm hoping this would be a clue to someone
here to get at least a direction for investigating...

Thanks.

-- 
Resistance is futile. You will be jazzimilated.

Lisp, Jazz, Aïkido: http://www.didierverna.info