# Pastebin 2EYAx3ea
(defun foo (x) nil)
FOO
CL-USER> (trace foo)
(FOO)
CL-USER> (foo 'a)
1> (FOO A)
<1 (FOO NIL)
NIL
CL-USER> (foo '(1 2 3 ))
1> (FOO #1=#1#)
<1 (FOO NIL)
NIL
CL-USER>