commafy.hs

{-# LANGUAGE BangPatterns #-}
module Main where
import Data.Char
import Data.List
import Data.List.Split
import Criterion.Main

commafyFoldr :: String -> String
commafyFoldr = snd . foldr f (0 :: Int, "")
  where
    f c (!m, cs)
      | m `mod` 3 == 0
      , m /= 0 = (m + 1, c:',':cs)
      | otherwise = (m + 1, c:cs)

commafySplit :: String -> String
commafySplit = reverse . intercalate "," . chunksOf 3 . reverse

main :: IO ()
main = defaultMain
  [ env setup $ \input -> bgroup "commafy"
    [ bench "foldr" $ nf commafyFoldr input
    , bench "split" $ nf commafySplit input
    ]
  ]

setup :: IO String
setup = return "0123456789"