Semantically grepping Emacs Lisp sources?

[Tim Landscheidt]

Hi,

from time to time, I'm looking for examples on how to solve
some problem in Emacs Lisp.  I have a Git checkout of Emacs
and ELPA, i. e. "good" code en masse.

So suppose I'm interested in actual uses of define-skeleton
or insert-skeleton where the skeleton's interactor is not a
string, or the skeleton contains some invocation of
completing-read; this is quite hard (and theoretically im-
possible) to turn into a regular expression.

In similar cases in the past, I have sometimes built ad-hoc
greps with directory-files, find-file-noselect and read, but
this is definitely overkill for just browsing around.

Is there a utility either integrated in Emacs or external
that instead of a regular expression accepts some form of
"predicate" and then highlights all Lisp structures that
match it?  I. e., something like (pseudo-code) "(and (eql
(car s) 'define-skeleton) (not (string-p (whatever s))))"?

TIA,
Tim