generic

   type Discrete_Type is (<>);

package Modulo_Discrete_Type is

type Discrete_Type is (<>);

function Succ_Mod 
(
D
: Discrete_Type) return Discrete_Type is (if D = Discrete_Type'Last then Discrete_Type'First else Discrete_Type'Succ (D));

function Pred_Mod 
(
D
: Discrete_Type) return Discrete_Type is (if D = Discrete_Type'First then Discrete_Type'Last else Discrete_Type'Pred (D));