tycon.hs

{-# LANGUAGE ExplicitForAll #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE AllowAmbiguousTypes #-}

module TyCon where

import GHC.Exts (Constraint)
import Data.Text (Text)

type family AcceptableKids kids tag :: Constraint where
    AcceptableKids kids "span" = kids ~ String
    AcceptableKids kids div = ()

ayyylmao :: forall tag kids. (Show kids, AcceptableKids kids tag) => kids -> IO ()
ayyylmao kids = print kids

main :: IO ()
main = do
    ayyylmao @"span" "gotta be a string my dude"
    ayyylmao @"div" [1, 2, 3]
    ayyylmao @"asdf" ("who are you even" :: Text)