Triplet.hs

module Data.Triplet where

import Control.Applicative
import Data.Foldable
import Data.Monoid
import Data.Traversable

data Triplet a = Triplet a a a
    deriving (Eq, Read, Show)

instance Functor Triplet where
    fmap f (Triplet l m r) = Triplet (f l) (f m) (f r)

instance Applicative Triplet where
    pure x = Triplet x x x
    Triplet fl fm fr <*> Triplet xl xm xr = Triplet (fl xl) (fm xm) (fr xr)

instance Foldable Triplet where
    foldMap f (Triplet l m r) = mconcat . map f $ [l, m, r]

instance Traversable Triplet where
    sequenceA (Triplet l m r) = Triplet <$> l <*> m <*> r