BenchStringToInt.hs

-- ghc -O --make BenchStringToInt.hs && ./BenchStringToInt --output bench_string_to_int.html&& open bench_string_to_int.html 

import Criterion.Main
import Data.Maybe (fromMaybe)
import Text.Parsec (parse)
import Text.Parsec.Token (makeTokenParser, integer)
import Text.Parsec.Language (haskellStyle)
import Data.Char (digitToInt, isDigit)

main = defaultMain [
  bgroup "string to int" [ bench "read"  $ nf withRead numbers
                         , bench "parsec"  $ nf withParse numbers
                         , bench "naive"  $ nf withDigitToInt numbers
                         ]
  ]

counts = [1..75000]

numbers = map show $ foldl1 (++) [counts, counts, counts, counts]

withRead :: [String] -> [Int]
withRead xs =
    map toInt' xs
  where
    toInt' s = read s :: Int

withParse :: [String] -> [Int]
withParse xs =
    map toInt' xs
  where
    toInt' = fromInteger . either (const 0) id . parse (integer . makeTokenParser $ haskellStyle) "integer"

withDigitToInt :: [String] -> [Int]
withDigitToInt xs = map (fromMaybe 0 . stringToInt) xs

stringToInt :: String -> Maybe Int
stringToInt xs
    | all isDigit xs = Just $ loop 0 xs
    | otherwise = Nothing
  where
    loop acc [] = acc
    loop acc xs' = foldl (\acc' x -> acc' * 10 + digitToInt x) acc xs'

Results

benchmarking string to int/read
time                 595.9 ms   (587.9 ms .. 608.0 ms)
                     1.000 R²   (1.000 R² .. 1.000 R²)
mean                 595.4 ms   (592.9 ms .. 597.1 ms)
std dev              2.510 ms   (0.0 s .. 2.898 ms)
variance introduced by outliers: 19% (moderately inflated)

benchmarking string to int/parsec
time                 433.3 ms   (420.9 ms .. 446.4 ms)
                     1.000 R²   (1.000 R² .. 1.000 R²)
mean                 427.9 ms   (422.9 ms .. 430.5 ms)
std dev              4.343 ms   (0.0 s .. 4.514 ms)
variance introduced by outliers: 19% (moderately inflated)

benchmarking string to int/naive
time                 14.43 ms   (14.08 ms .. 14.77 ms)
                     0.997 R²   (0.995 R² .. 0.999 R²)
mean                 14.29 ms   (14.13 ms .. 14.47 ms)
std dev              398.1 μs   (335.5 μs .. 493.0 μs)