Hello! I saw a question on StackOverflow about the difference between isAlpha and isLetter today. One of the answers stated that the two functions are interchangeable, even though they are implemented differently. I decided to find out whether the difference in implementation influences performance, and look what I found:
import Criterion.Main import Data.Char fTest name f list = bgroup name $ map (\(n,c) -> bench n $ whnf f c) list tests = [("latin", 'e'), ("digit", '8'), ("symbol", '…'), ("greek", 'λ')] main = defaultMain [fTest "isAlpha" isAlpha tests, fTest "isLetter" isLetter tests]
produces this table (times are in nanoseconds): latin digit symbol greek ----- ----- ------ ----- isAlpha | 156 212 368 310 isLetter | 349 344 383 310 isAlpha is twice as fast on latin inputs! Does it mean that isAlpha should be preferred? Why isn’t isLetter defined in terms of isAlpha in Data.Char?