free monad list, uses product type

gistfile1.hs

import Control.Monad.Free
import Test.QuickCheck

-- tuple based free list
type Nil = ()
nilWitness = ()

data Pair a b = Pair a b
type Ftor = Pair
--type Ftor a  = (,) a
type TList a = Free (Ftor a) Nil

toL :: TList a -> [a]
toL (Pure nilWitness) = []
toL (Free (Pair a next)) = a : (toL next)

fromL :: [a] -> TList a
fromL [] = Pure nilWitness
fromL (x:xs) = Free (Pair x (fromL xs))

-- quickCheck (\l -> (toL . fromL $ l) == l)