Cyclical data structure, I saw this on some SO answer

cyclical-from-enum.hs

 class (Enum a, Bounded a, Eq a) => Cyclical a where
   next :: a -> a
   next a = if a == maxBound then minBound else succ a
   prev :: a -> a
   prev a = if a == minBound then maxBound else pred a

 data Direction = North | East | South | West
     deriving (Show, Enum, Bounded, Eq)

 instance Cyclical Direction