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

0readme.md

Emulating the elegance of JavaScript's new Array in Haskell

What does new Array(x) do? Trick question. It does different things depending on whether x is an integer or something else.

I wanted to replicate this elegant functionality in Haskell: behold.

EvilList.hs

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

module EvilList where

import Data.Typeable

type family EvilList a where
  EvilList Int = [()]
  EvilList a   = [a]

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

Why have you done this?

:(

Now make it accept variable number of arguments.