Type Aligned List of Func

{-# LANGUAGE GADTs, KindSignatures #-}

data TAList :: (* -> * -> *) -> * -> * -> * where
  Nil   :: TAList c x x
  (:::) :: c x y -> TAList c y z -> TAList c x z

infixr 5 :::

newtype Func a b = Func { unFunc :: a -> b }

foldTAList :: a -> TAList Func a b -> b
foldTAList acc Nil = acc
foldTAList acc (h ::: t) = foldTAList (unFunc h acc) t

half x = fromIntegral x / 2 :: Rational
oneThird x = fromRational x / 3 :: Double


flow :: TAList Func Int String
flow  = Func half ::: Func oneThird ::: Func show ::: Nil

main = print $ foldTAList 12 flow