Experiments with OverloadedLabels

OverloadedLabels.hs

{-# LANGUAGE OverloadedLabels #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
module Main where

import GHC.OverloadedLabels

data Foo = Foo
         {
            _bar :: String
         ,  _baz :: Int
         }

-- https://ghc.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields/OverloadedLabels
-- 
-- *Main> :t #baz
-- #baz :: IsLabel "baz" t => t
instance IsLabel "baz" (Foo -> Int) where
    fromLabel _ =  _baz

instance IsLabel "odd" (Foo -> Int) where
    fromLabel _ =  _baz

instance IsLabel "odd" (Foo -> String) where
    fromLabel _ =  _bar


fooval :: Foo
fooval = Foo "foo" 5

main :: IO ()
main = do
    print (#baz fooval :: Int)
    -- The following is a bit odd
    print (#odd fooval :: Int)
    print (#odd fooval :: String)