A Lisp object.
A ring object created by make-ring.
ring-push adds any Lisp object as an element of the ring before the "insertion position", which means that a following ring-pop will return it. If the ring is full, that is the number of elements in the ring is the same as its size (see make-ring), then
ring-push first removes the element after the insertion point.
Once it finished modifying the ring, if
ring-push removed an element and there is a delete-function (see make-ring), then
ring-push calls delete-function on the element that it removes.
LispWorks User Guide and Reference Manual - 20 Sep 2017