File: listp

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R4RS 6.3  (list? object)  ==>  boolean

Returns #T if OBJECT is a list, otherwise returns #F. By definition,
all lists have finite length and are terminated by the empty list.

(list? '(a b c))      ==>  #t
(list? '())           ==>  #t
(list? '(a . b))      ==>  #f
(let ((x (list 'a)))
  (set-cdr! x x)
  (list? x))          ==>  #f