HListCurry.hs

{-# LANGUAGE TypeFamilies, DataKinds, TypeOperators #-}

module HListCurry
  ( HListElim
  , hListCurry
  , example
  ) where

import Data.HList

type family HListElim (ts :: [*]) (a :: *) :: *
type instance HListElim '[] a = a
type instance HListElim (t ': ts) a = t -> HListElim ts a

hListCurry :: HListElim ts a -> HList ts -> a
hListCurry f HNil = f
hListCurry f (HCons x xs) = hListCurry (f x) xs

example :: String
example = hListCurry (\i s -> show i ++ s) (HCons (3 :: Int) (HCons "hallo" HNil))