type: system constant location: built-in source file: xlsym.c Common LISP compatible: yes supported on: all machines
The NIL constant represents the empty list or the false value - as oppossed to the true value (the symbol T). NIL can be writen as the 3 character symbol NIL or as the empty list ().
(setq myvar NIL) ; set MYVAR to False (setq myvar 'NIL) ; NIL and 'NIL evaluate to NIL (setq myvar ()) ; () is the empty list = NIL (setq myvar '()) ; () and '() evaluate to NIL (if nil (print "this won't print") ; if/then/else (print "this will print"))
NOTE: You can not change the value of NIL.