A positive fixnum.
A function designator for a function of one argument.
size is the maximum number of elements that the ring ring can hold. Once ring has this number of elements, if an element is added to ring (by ring-push), an element is first removed from the ring.
name simply names the ring, but has no effect on its functionality. It is used when printing the ring object, and is returned by ring-name.
delete-function, if supplied, is called each time an element is removed from the ring (by ring-push) because it is full. The default value of delete-function is
The ring keeps the elements in a logical ring with an "insertion position". The function ring-push adds an element before the insertion position. If the ring is full, it first removes the element immediately after the insertion position.
The function ring-pop removes from the ring the element before the insertion point, and returns that element. Thus when using ring-push and ring-pop on their own, the ring behaves like a stack with limited length.
rotate-ring can be used to move the insertion point. ring-ref can be used to index into the ring. map-ring, position-in-ring, and position-in-ring-forward can be used to iterate through the ring's elements.
All access to a ring is thread-safe. Therefore access to a ring may hang if another process keeps it locked. If you need to guarantee no hanging, you can use with-ring-locked with non-nil timeout around the critical calls.
LispWorks User Guide and Reference Manual - 13 Feb 2015