Going from a type implementing Generic1 to a Holey (which can be used to get a Zipper for free)

GenericZipper.hs

{-# LANGUAGE TypeSynonymInstances, FlexibleInstances, MultiParamTypeClasses, TypeOperators, FlexibleContexts, TypeFamilies #-}
module FunctorCombo.Generic (
  encode
) where

import GHC.Generics
import qualified FunctorCombo.Functor as F

class Encode gen where
  type DerG gen :: * -> *
  encode :: gen a -> DerG gen a


instance Encode (Rec0 c) where
  type DerG (Rec0 c) = F.Const c
  encode (K1 c) = F.Const c

instance Encode Par1 where
  type DerG Par1 = F.Id
  encode (Par1 r) = F.Id r


instance Functor f => Encode (Rec1 f) where
  type DerG (Rec1 f) = (f F.:. F.Id)
  encode (Rec1 fp) = F.O $ fmap F.Id fp


instance Encode (f :+: g) where
  type DerG (f :+: g) = (f F.:+: g)
  encode (L1 fp) = F.InL fp
  encode (R1 fp) = F.InR fp

instance Encode (f :*: g) where
  type DerG (f :*: g) = (f F.:*: g)
  encode (fp :*: gp) = fp F.:*: gp

instance Encode (f :.: g) where
  type DerG (f :.: g) = (f F.:. g)
  encode (Comp1 fgp) = F.O fgp