record accessor shenanigans inspired by https://github.com/ghc-proposals/ghc-proposals/pull/282

RecordSlash.hs

{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedLabels #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}

module Main where

import GHC.OverloadedLabels
import GHC.Records
import Prelude hiding ((/))

newtype Access r v = Access (r -> v)

instance HasField label r v => IsLabel label (Access r v) where
  fromLabel = Access (getField @label)

(/) :: r -> Access r v -> v
(/) r (Access f) = f r

data Person = Person {name :: String, address :: Address}

data Address = Address {street :: String, number :: Int}

main :: IO ()
main = do
  let person = Person { name = "foo", address = Address "bar" 3 }
  print $ person / #address / #street