Pretty straightforward:
$ (has-param "foo") nil $ (set-param "foo" 42) 42 $ (has-param "foo") t $ (get-param "foo") 42 $ (delete-param "foo") $ (has-param "foo") nil
The S-XML-RPC library is used for communicating with the parameter server and converting XML-RPC types to Lisp objects. Most of the type mappings are straightforward: strings to strings, arrays to lists, etc. See the table at the link above for the full list.