Promoted MuRef

muref.hs

#!/usr/bin/env stack
-- stack --install-ghc ghci --package data-reify

{-# LANGUAGE InstanceSigs        #-}
{-# LANGUAGE RankNTypes          #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications    #-}
{-# LANGUAGE TypeFamilies        #-}

import           Data.Reify
import           Data.Functor.Compose

instance MuRef a => MuRef [a] where
    type DeRef [a] = Compose [] (DeRef a)

    mapDeRef
        :: forall f u. Applicative f
        => (forall b. (MuRef b, Compose [] (DeRef a) ~ DeRef b) => b -> f u)
        -> [a]
        -> f (Compose [] (DeRef a) u)
    mapDeRef f = fmap Compose . traverse go
      where
        go :: a -> f (DeRef a u)
        go = mapDeRef @a $ \(x :: b) -> f @[b] [x]

main :: IO ()
main = putStrLn "hi"