hello_world.hs

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverloadedLabels #-}
{-# LANGUAGE BlockArguments #-}
{-# LANGUAGE UnicodeSyntax #-}
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE ExplicitNamespaces #-}
{-# LANGUAGE RoleAnnotations #-}

import GHC.OverloadedLabels (type IsLabel, fromLabel)
import GHC.TypeLits (pattern SomeSymbol, type Symbol, type KnownSymbol)
import Data.Kind (type Type)
import Data.Proxy (pattern Proxy, type Proxy)

type role With nominal
data With ∷ Symbol → Type where
  With ∷ ∀ (symbol ∷ Symbol). With symbol

instance KnownSymbol symbol ⇒ Show (With symbol) where
  show = const do show do SomeSymbol do Proxy @symbol

instance IsLabel symbol (With symbol) where
  fromLabel = With @symbol

main = print hello'world
  where
    hello'world = #hello'world ∷ With "hello'world"