Generalized uncurry without OverlappingInstances or other evil extensions

guncurry.hs

{-# LANGUAGE DataKinds, TypeFamilies, MultiParamTypeClasses, FlexibleInstances, GADTs, TypeOperators, FlexibleContexts, ConstraintKinds #-}

import Data.Tagged

type family FunResult f where
  FunResult (a -> b) = FunResult b
  FunResult x = x

type family FunArgs f where
  FunArgs (a -> b) = a ': FunArgs b
  FunArgs x = '[]

data HList ts where
  Nil :: HList '[]
  Cons :: t -> HList ts -> HList (t ': ts)

class Uncurry' (as :: [ * ]) o f where
  guncurry' :: Tagged as (f -> HList as -> o)

instance Uncurry' as o b => Uncurry' (a ': as) o (a -> b) where
  guncurry' = Tagged $ \f (x `Cons` xs) -> untag guncurry' (f x) xs

instance Uncurry' '[] r r where
  guncurry' = Tagged $ \x Nil -> x

type Uncurry as o f = (as ~ FunArgs f, o ~ FunResult f, Uncurry' as o f)
type as =-> o = HList as -> o

guncurry :: Uncurry as o f => f -> as =-> o 
guncurry = untag guncurry'