Config with generics-sop

gsop.hs

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveGeneric #-}

module Foo where

import Control.Monad
import qualified GHC.Generics as GHC
import qualified Generics.SOP as SOP
import qualified Generics.SOP.NS as NS

import Data.Functor.Identity

type AppSettings = AppSettings_ Identity

-- Squash Identity
type family SQ f t where
  SQ Identity t = t
  SQ f t = f t

data AppSettings_ f = AppSettings
  { port :: SQ f Int
  , host :: SQ f String
  } deriving GHC.Generic

instance SOP.Generic (AppSettings_ f)

as :: AppSettings_ Maybe
as = AppSettings (Just 2) (Just "foo")

fff :: AppSettings_ Maybe -> Maybe AppSettings
fff = fmap SOP.to . NS.sequence'_SOP . NS.fromI_SOP . SOP.from

baz2 :: Maybe AppSettings
baz2 = fff as

maybePort :: Maybe Int
maybePort = port <$> baz2