$ clisp
 
 <...snip...>

[1]> (load "filter.l")
;; Loading file filter.l ...
;; Loaded file filter.l
T
[2]> (filter #'null '(hi 1 3 bye "apples" (1 2 good) NIL "boo"))
(NIL)
[3]> (filter #'null '(hi 1 3 bye "apples" NIL (1 2 good) NIL "boo"))
(NIL NIL)
[4]> (filter #'atom '(hi 1 3 bye "apples" NIL (1 2 good) NIL "boo"))
(HI 1 3 BYE "apples" NIL NIL "boo")
[5]> (filter #'symbolp '(hi 1 3 bye "apples" NIL (1 2 good) NIL "boo"))
(HI BYE NIL NIL)
[6]> (filter #'numberp '(hi 1 3 bye "apples" NIL (1 2 good) NIL "boo"))
(1 3)
[7]> (filter #'stringp '(hi 1 3 bye "apples" NIL (1 2 good) NIL "boo"))
("apples" "boo")
[8]> (filter #'listp '(hi 1 3 bye "apples" NIL (1 2 good) NIL "boo"))
(NIL (1 2 GOOD) NIL)
[9]> (bye)
Bye.