OverloadedLabels.hs

{-# LANGUAGE OverloadedLabels  #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables #-}
import Data.String
import GHC.OverloadedLabels
import GHC.TypeLits
import Data.Proxy
data Html = Html String [String] [Html] | String String deriving (Show)

--     Expected type: [inner] -> Html
--        Actual type: [String] -> [Html] -> Html
--    • Probable cause: ‘Html’ is applied to too few arguments

instance IsString Html where fromString = String

instance (KnownSymbol symbol,attr ~ String,inner ~ Html) => IsLabel symbol ([attr] -> [inner] -> Html) where
  fromLabel p = Html (symbolVal' (Proxy :: Proxy symbol))

instance (KnownSymbol symbol,attr ~ String,inner ~ Html) => IsLabel symbol ([inner] -> Html) where
  fromLabel p = Html (symbolVal' p) []