File System Traversal Map/Collect

[Nordlöw]

I am trying to construct a general file system traversal function
which operates (map/collect) on each file using a function as
argument. Such a function could be query-replace-regexp() specializing
it to the functions found in findr.el. If have looked at findr.el but
I find its common-lisp-inner-loop difficult to understand; Clearly not
functional programming. I understand why some want to clean out the
common-lisp parts of GNU Emacs. Basically I am recursively calling
directory-files(). I would like the function to support both breadth-
and depth-first traversals.

Does such a logic already exist somewhere?

My own current main motivation is that I want to extend the
functionality of findr.el to skip certain directory- and file-
patterns.

I would also, if possible, generalize its use through TRAMP using
tramp-handle-directory-files() instead of directory-files().

Thanks in advance,
Nordlöw