Truthy And Falsy in

About Truthy And Falsy

In Common Lisp, false values are represented by the empty list – () – or the symbol nil. These values can be quoted or unquoted.

;; Equivalent False Values
()   ; => NIL
nil  ; => NIL
'()  ; => NIL
'nil ; => NIL

All other values in Lisp represent truth. There also exists the special constant symbol t that is always equal to t (and is therefore always true).

;; Some Different True Values
42                        ; => 42
"this statement is false" ; => "this statement is false"
t                         ; => T
't                        ; => T