お試し2 inspired by https://qiita.com/mod_poppo/items/03fc14f693b601e0a00f

StateVSIORef.hs

{-# LANGUAGE LambdaCase #-}

module Bench.StateVSIORef where

import Data.IORef
import Control.Monad.State.Strict


n :: Int
n = 2 ^ (31 :: Int)

type Acc = Either () Ordering

f :: Acc -> Acc
f = \case
  Left _   -> Right EQ
  Right EQ -> Right LT
  Right LT -> Right GT
  Right GT -> Left ()

e :: Acc
e = Right LT

someCalculationWithState :: IO Acc
someCalculationWithState = flip evalStateT e $ do
  forM_ [0..n] $ \_ -> do
    modify' f
  get

someCalculationWithIORef :: IO Acc
someCalculationWithIORef = do
  accRef <- newIORef e
  forM_ [0..n] $ \_ -> do
    modifyIORef' accRef f
  readIORef accRef

someCalculationWithRec :: IO Acc
someCalculationWithRec = return $ loop 0 e
  where
    loop i acc
      | i == n    = f acc
      | otherwise = loop (i + 1) $ f acc