RecordFields.hs

{-# LANGUAGE DataKinds             #-}
{-# LANGUAGE DuplicateRecordFields #-}
{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedLabels      #-}
{-# LANGUAGE ScopedTypeVariables   #-}
{-# LANGUAGE TypeApplications      #-}
{-# OPTIONS_GHC -fno-warn-orphans  #-}

module Rec where

import           GHC.OverloadedLabels
import           GHC.Records


instance HasField s r a => IsLabel s (r -> a) where
    fromLabel = getField @s


data Person = Person { name :: String, age :: Int }

data Group = Group { name :: String, members :: [Person] }


spyro :: Person
spyro = Person "Spyro" 7

hisName :: String
hisName = #name spyro

-- now DataKinds, FlexibleContexts needed

getName :: HasField "name" r String => r -> String
getName = #name