Is there a "selective setq locator/highlighter" anywhere?

[Alan Mackenzie <acm@muc.de>]

Hi, Emacs!

I sometimes have problems with long rambling elisp defuns, in that some
critical variable, say `c-state-cache' is updated in several (or even
many) places in the defun, and it's difficult to see the places it gets
changed.

Hi-lock-mode is helpful here, in that I can highlight occurances of
"c-state-cache" and occurances of "setq".  But the longer and ramblinger
a defun becomes, the less helpful is this.

I would like a tool which would highlight these:

    (setq foo bar
          c-state-cache (cdr c-state-cache))
    (setcar c-state-cache (caar c-state-cache))

, but not this:

    (setq old-cache c-state-cache)

.  Does anybody know of anything like this in existance?

Thanks!

-- 
Alan Mackenzie (Nuremberg, Germany).