Emulating the elegance of JavaScript's `new Array` in Haskell

EvilList.hs

{-# LANGUAGE FlexibleContexts, ScopedTypeVariables, TypeApplications, TypeFamilies #-}

module EvilList where

import Data.Typeable

type family EvilListContent a where
  EvilListContent Int = ()
  EvilListContent a = a

-- | Emulating the elegance of JavaScript's @new Array@.
--
-- >>> evilList (5 :: Int)
-- [(),(),(),(),()]
--
-- >>> evilList "hello"
-- ["hello"]
evilList :: forall a. (Typeable a, Typeable (EvilListContent a)) => a -> [EvilListContent a]
evilList a
  | Just Refl <- eqT @a @Int = replicate a ()
  | Just Refl <- eqT @a @(EvilListContent a) = [a]
  | otherwise = undefined