Church encoded free monads vs not

Church.hs

-- runs fast
{-# LANGUAGE DeriveFunctor     #-}
{-# LANGUAGE FlexibleContexts  #-}
{-# LANGUAGE TemplateHaskell   #-}

module Main where

import Control.Monad
import Control.Monad.Free.Church
import Control.Monad.Free.TH

data DslCmd next =
  GetValue'
    Int
    (Int -> next) 
  deriving (Functor)

makeFree ''DslCmd

type DslCmdM = F DslCmd

myProgram :: DslCmdM [Int]
myProgram = loop [0..1000000]
 where loop = mapM getValue'

runCmd :: DslCmd (IO a) -> IO a
runCmd (GetValue' v n) = n (2 * v)

main :: IO ()
main = do
  r <- iterM runCmd myProgram
  print $ sum r
  return ()

Free.hs

-- runs really slow
{-# LANGUAGE DeriveFunctor     #-}
{-# LANGUAGE FlexibleContexts  #-}
{-# LANGUAGE TemplateHaskell   #-}

module Main where

import Control.Monad
import Control.Monad.Free
import Control.Monad.Free.TH

data DslCmd next =
  GetValue'
    Int
    (Int -> next) 
  deriving (Functor)

makeFree ''DslCmd

type DslCmdM = Free DslCmd

myProgram :: DslCmdM [Int]
myProgram = loop [0..1000000]
 where loop = mapM getValue'

runCmd :: DslCmd (IO a) -> IO a
runCmd (GetValue' v n) = n (2 * v)

main :: IO ()
main = do
  r <- iterM runCmd myProgram
  print $ sum r
  return ()