module Ring (
   Ring, Elt,
   newRing,
   current, deleteCurrent,
   rotate, size) where

----------------------------------------
-- Interface
----------------------------------------

newRing       :: [Elt] -> Ring
current       :: Ring -> Elt
deleteCurrent :: Ring -> Ring   -- after deleting, new current is the
                                -- element following the deleted elt
rotate        :: Ring -> Int -> Ring
size          :: Ring -> Int

----------------------------------------
-- Implementation
----------------------------------------

----------------------
-- type implementation
----------------------
type Elt = Int
type Ring = [Elt]

--------------------------
-- Function implementation
--------------------------
newRing elts           = elts
current (first:_)      = first
deleteCurrent (_:rest) = rest

rotate elts amount  = newFront++newRear
   where
      modAmount = amount `mod` ringSize
      ringSize  = length elts
      newFront  = drop modAmount elts
      newRear   = take modAmount elts

size elts = length elts