-
-@node Rings
-@section Managing a Fixed-Size Ring of Objects
-
-@cindex ring data structure
- This section describes functions for operating on rings. A
-@dfn{ring} is a fixed-size data structure that supports insertion,
-deletion, rotation, and modulo-indexed reference and traversal.
-
-@defun make-ring size
-This returns a new ring capable of holding @var{size} objects.
-@var{size} should be an integer.
-@end defun
-
-@defun ring-p object
-This returns @code{t} if @var{object} is a ring, @code{nil} otherwise.
-@end defun
-
-@defun ring-size ring
-This returns the maximum capacity of the @var{ring}.
-@end defun
-
-@defun ring-length ring
-This returns the number of objects that @var{ring} currently contains.
-The value will never exceed that returned by @code{ring-size}.
-@end defun
-
-@defun ring-elements ring
-This returns a list of the objects in @var{ring}, in order, newest first.
-@end defun
-
-@defun ring-copy ring
-This returns a new ring which is a copy of @var{ring}.
-The new ring contains the same (@code{eq}) objects as @var{ring}.
-@end defun
-
-@defun ring-empty-p ring
-This returns @code{t} if @var{ring} is empty, @code{nil} otherwise.
-@end defun
-
- The newest element in the ring always has index 0. Higher indices
-correspond to older elements. Indices are computed modulo the ring
-length. Index @minus{}1 corresponds to the oldest element, @minus{}2
-to the next-oldest, and so forth.
-
-@defun ring-ref ring index
-This returns the object in @var{ring} found at index @var{index}.
-@var{index} may be negative or greater than the ring length. If
-@var{ring} is empty, @code{ring-ref} signals an error.
-@end defun
-
-@defun ring-insert ring object
-This inserts @var{object} into @var{ring}, making it the newest
-element, and returns @var{object}.
-
-If the ring is full, insertion removes the oldest element to
-make room for the new element.
-@end defun
-
-@defun ring-remove ring &optional index
-Remove an object from @var{ring}, and return that object. The
-argument @var{index} specifies which item to remove; if it is
-@code{nil}, that means to remove the oldest item. If @var{ring} is
-empty, @code{ring-remove} signals an error.
-@end defun
-
-@defun ring-insert-at-beginning ring object
-This inserts @var{object} into @var{ring}, treating it as the oldest
-element. The return value is not significant.
-
-If the ring is full, this function removes the newest element to make
-room for the inserted element.
-@end defun
-
-@cindex fifo data structure
- If you are careful not to exceed the ring size, you can
-use the ring as a first-in-first-out queue. For example:
-
-@lisp
-(let ((fifo (make-ring 5)))
- (mapc (lambda (obj) (ring-insert fifo obj))
- '(0 one "two"))
- (list (ring-remove fifo) t
- (ring-remove fifo) t
- (ring-remove fifo)))
- @result{} (0 t one t "two")
-@end lisp