{-# LANGUAGE DataKinds, FlexibleContexts, TemplateHaskell, TypeFamilies, TypeOperators #-}
import Data.Extensible
import Data.Monoid
import Control.Monad.Identity

mkField "a b"

-- hsequence
type FS = ["a" :> Integer, "b" :> String]

r1, r2 :: Comp First (Field Identity) :* FS
r1 = a <@=> First (Just 1)
       <: b <@=> mempty
       <: Nil

r2 = a <@=> First (Just 5)
  <: b <@=> First (Just "x")
  <: Nil

{-

>>> r1r2

Just (a @= 1 <: b @= "x" <: Nil)
-}
r1r2 = getFirst
    $ hsequence
    $ hzipWith (\ (Comp x) (Comp y) -> Comp (x <> y))
        r1 r2