tuple arithmetic via generics

TuplePlus.hs

{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE TypeOperators #-}

module TuplePlus where

import GHC.Generics

class GTuplePlus f where
  gplus :: f p -> f p -> f p

instance (Num c) => GTuplePlus (K1 i c) where
  gplus (K1 x) (K1 y) = K1 (x + y)

instance GTuplePlus f => GTuplePlus (M1 i t f) where
  gplus (M1 x) (M1 y) = M1 (x `gplus` y)

instance (GTuplePlus f, GTuplePlus g) => GTuplePlus (f :*: g) where
  gplus (f :*: g) (f' :*: g') = (f `gplus` f') :*: (g `gplus` g')

plus :: (Generic a, GTuplePlus (Rep a)) => a -> a -> a
plus a b = to (from a `gplus` from b)
{-# SPECIALIZE plus :: (Int, Int, Int) -> (Int, Int, Int) -> (Int, Int, Int) #-}
{-# SPECIALIZE plus :: (Int, Int, Int, Int) -> (Int, Int, Int, Int) -> (Int, Int, Int, Int) #-}
{-# SPECIALIZE plus :: (Int, Int, Int, Int, Int) -> (Int, Int, Int, Int, Int) -> (Int, Int, Int, Int, Int) #-}