triplet.hs

module Triplet
where
import List

newtype Triplet = Triplet Int
  deriving(Show,Read)
instance Eq Triplet where
  Triplet i == Triplet j = i == j
instance Ord Triplet where
  (Triplet i) `compare` (Triplet j)
    | (triplet i) < (triplet j) = LT
    | (triplet i) > (triplet j) = GT
    | otherwise                 = compare i j
    where triplet x = (x `mod` 3)

test = List.sortBy compare [Triplet x|x<-[3,1,2,6,7,8,9]]