Add a filter function to emacs

[Rolando Pereira <ei08150@fe.up.pt>]

Hello,

I would like to know if there is a reason for the lack of a filter
function on the emacs code base.

According to the Elisp Cookbook on the Emacs Wiki, it seems that it
would be simple to implement:

  (defun my-filter (condp lst)
    (delq nil
          (mapcar (lambda (x) (and (funcall condp x) x)) lst)))
;; From http://www.emacswiki.org/emacs/ElispCookbook

Shouldn't this function be in the regular emacs code base (maybe in the
lisp/simple.el file)?

Is there any problem with it?