+val pre = ref (fn _ : {nodes : string list, id : string, hostname : string} => ())
+fun registerPre f =
+ let
+ val old = !pre
+ in
+ pre := (fn x => (old x; f x))
+ end
+
+val post = ref (fn () => ())
+fun registerPost f =
+ let
+ val old = !post
+ in
+ post := (fn () => (old (); f ()))
+ end
+
+val aliaser = ref (fn _ : string => ())
+fun registerAliaser f =
+ let
+ val old = !aliaser
+ in
+ aliaser := (fn x => (old x; f x))
+ end
+