Strict foldMap benchmark

strict_fold_map.hs

{-# LANGUAGE BangPatterns #-}

{-# OPTIONS_GHC -O2 #-}

import Gauge
import Data.Foldable
import qualified Data.Set as S

foldMap' :: (Monoid m, Foldable f) => (a -> m) -> f a -> m
foldMap' f = foldl' (\ !acc a -> acc <> f a) mempty

numbers :: [Int]
numbers = [1..4000]

intToSet :: Int -> S.Set Int
intToSet i = S.singleton (mod i 10)

main :: IO ()
main = defaultMain
  [ bench "lazy" $ whnf (foldMap intToSet) numbers
  , bench "strict" $ whnf (foldMap' intToSet) numbers
  ]