Maybeize a product

MaybeizeProduct.hs

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE PartialTypeSignatures #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}
{-# OPTIONS_GHC -Wno-partial-type-signatures #-}

module Main where

import qualified GHC.Generics
import Generics.SOP
import Generics.SOP.Constraint
import Generics.SOP.NP

maybeizeProduct :: forall r xs r' ys. (IsProductType r xs, IsProductType r' ys, AllZip Maybeized xs ys) => r -> r'
maybeizeProduct = productTypeTo @r' . trans_NP (Proxy @Maybeized) (mapII maybeize) . productTypeFrom @r

class (b ~ Maybe a) => Maybeized a b where
  maybeize :: a -> b

instance Maybeized a (Maybe a) where
  maybeize = Just

main :: IO ()
main = do
  print $ (maybeizeProduct ('a', 'b') :: (_,_))
  print $ (maybeizeProduct ('a', 'b', 'c') :: (_,_,_))