Verifies that an item is a list
(listp item)
Arguments
Any atom, list, or expression.
Return Values
T if item is a list; otherwise nil. Because nil is both an atom and a list, the listp function returns T when passed nil.
Examples
Command: (listp '(a b c))
T
Command: (listp 'a)
nil
Command: (listp 4.343)
nil
Command: (listp nil)
T
Command: (listp (setq v1 '(1 2 43)))
T
The vl-list* and vl-list-length functions.
