[SBCL] CL-USER> (defpackage "" (:export :foo)) 
#<PACKAGE ""> 
 
[SBCL] CL-USER> (defun ||:foo () (print 'foo)) 
WARNING: redefining ||:FOO in DEFUN 
||:FOO 
 
[SBCL] CL-USER> (||:foo) 
 
FOO 
FOO 
 
[SBCL] CL-USER> (:foo) 
 
debugger invoked on a UNDEFINED-FUNCTION in thread 
#<THREAD "main thread" RUNNING {10005204C3}>: 
  The function :FOO is undefined. 
 
restarts (invokable by number or by possibly-abbreviated name): 
  0: [CONTINUE ] Retry using :FOO. 
  1: [USE-VALUE] Use specified function 
  2: [ABORT    ] Exit debugger, returning to top level. 
 
(SB-IMPL::RETRY-%COERCE-NAME-TO-FUN :FOO NIL) 
0]