Really ugly Het Compose thing

HetComp.hs

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE DataKinds #-}

module HetComp where

type family as ++ bs :: [k] where
  '[]       ++ bs = bs
  (a ': as) ++ bs = a ': (as ++ bs)

data Comp :: [*] -> * -> * where
  Inj  :: (a -> b) -> Comp '[a] b
  Id   :: Comp '[a] a
  Comp :: Comp as x -> Comp (x ': bs) r -> Comp (as ++ (x ': bs)) r

(>>>) :: Comp as x -> Comp (x ': bs) r -> Comp (as ++ (x ': bs)) r
(>>>) = Comp

infixr 9 >>>

ex1 :: Comp [Int, Int, Int, Int] Int
ex1 = Inj (+1) >>> Inj (+1) >>> Id >>> Inj (+1)