Function arguments to HList (i-am-tom's work)

ArgsToHList.hs

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableInstances #-}
module ArgsToHList where

import Prelude hiding (uncurry)
import Data.Kind (Type)

data HList (xs :: [Type]) where
  HNil :: HList '[]
  HCons :: x -> HList xs -> HList (x ': xs)

class HUncurry (before :: Type) (after :: Type) (inputs :: [Type])
      | before after -> inputs where
  hUncurry :: before -> (HList inputs -> after)

instance {-# incoherent #-} (a ~ b, c ~ '[]) => HUncurry a b c where
  hUncurry = const

instance ( HUncurry a b c
         , d ~ ( x ': c )
         ) => HUncurry (x -> a) b d where
  hUncurry before (HCons x xs) = hUncurry (before x) xs

f :: Int -> Bool -> Char -> String
f i b c = show i <> show b <> show c