Calls a function on each element of a ring, modifying the element.
map-ring ring function
A ring object created by make-ring.
A function designator for a function of one argument.
map-ring funcalls the function function on each element in the ring in turn, and sets that ring element to the result.
function is called with the ring locked.
If you do not intend to modify the elements of ring, ensure that function returns its argument.
LispWorks User Guide and Reference Manual - 20 Sep 2017