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7.5.3.2 Predicates

   The procedures in this section test specific properties of lists.

   Scheme Procedure: proper-list? obj[12] ¶
          Return #t if obj is a proper list, or #f otherwise. This is the same as
          the core list? (see [13]List Predicates).

          A proper list is a list which ends with the empty list () in the usual
          way. The empty list () itself is a proper list too.

(proper-list? '(1 2 3))  => #t
(proper-list? '())       => #t

   Scheme Procedure: circular-list? obj[14] ¶
          Return #t if obj is a circular list, or #f otherwise.

          A circular list is a list where at some point the cdr refers back to a
          previous pair in the list (either the start or some later point), so that
          following the cdrs takes you around in a circle, with no end.

(define x (list 1 2 3 4))
(set-cdr! (last-pair x) (cddr x))
x => (1 2 3 4 3 4 3 4 ...)
(circular-list? x)  => #t

   Scheme Procedure: dotted-list? obj[15] ¶
          Return #t if obj is a dotted list, or #f otherwise.

          A dotted list is a list where the cdr of the last pair is not the empty
          list (). Any non-pair obj is also considered a dotted list, with length
          zero.

(dotted-list? '(1 2 . 3))  => #t
(dotted-list? 99)          => #t

   It will be noted that any Scheme object passes exactly one of the above three
   tests proper-list?, circular-list? and dotted-list?. Non-lists are dotted-list?,
   finite lists are either proper-list? or dotted-list?, and infinite lists are
   circular-list?.

   Scheme Procedure: null-list? lst[16] ¶
          Return #t if lst is the empty list (), #f otherwise. If something else
          than a proper or circular list is passed as lst, an error is signalled.
          This procedure is recommended for checking for the end of a list in
          contexts where dotted lists are not allowed.

   Scheme Procedure: not-pair? obj[17] ¶
          Return #t is obj is not a pair, #f otherwise. This is shorthand notation
          (not (pair? obj)) and is supposed to be used for end-of-list checking in
          contexts where dotted lists are allowed.

   Scheme Procedure: list= elt= list1 ...[18] ¶
          Return #t if all argument lists are equal, #f otherwise. List equality is
          determined by testing whether all lists have the same length and the
          corresponding elements are equal in the sense of the equality predicate
          elt=. If no or only one list is given, #t is returned.
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References

   1. http://www.gnu.org/software/guile/manual/html_node/index.html
   2. http://www.gnu.org/software/guile/manual/html_node/Concept-Index.html
   3. http://www.gnu.org/software/guile/manual/html_node/index.html#SEC_Contents
   4. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1.html
   5. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Selectors.html
   6. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Constructors.html
   7. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Selectors.html
   8. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Constructors.html
   9. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1.html
  10. http://www.gnu.org/software/guile/manual/html_node/index.html#SEC_Contents
  11. http://www.gnu.org/software/guile/manual/html_node/Concept-Index.html
  12. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Predicates.html#index-proper_002dlist_003f
  13. http://www.gnu.org/software/guile/manual/html_node/List-Predicates.html
  14. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Predicates.html#index-circular_002dlist_003f
  15. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Predicates.html#index-dotted_002dlist_003f
  16. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Predicates.html#index-null_002dlist_003f
  17. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Predicates.html#index-not_002dpair_003f
  18. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Predicates.html#index-list_003d
  19. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Selectors.html
  20. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1-Constructors.html
  21. http://www.gnu.org/software/guile/manual/html_node/SRFI_002d1.html
  22. http://www.gnu.org/software/guile/manual/html_node/index.html#SEC_Contents
  23. http://www.gnu.org/software/guile/manual/html_node/Concept-Index.html