On 11/21/12 4:59 PM, Artyom Kazak wrote:
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?
FWIW, testing on an arbitrary snippit of Japanese yields:
benchmarking nf (map isAlpha)
mean: 26.21897 us, lb 26.17674 us, ub 26.27707 us, ci 0.950
std dev: 251.4027 ns, lb 200.4399 ns, ub 335.3004 ns, ci 0.950
benchmarking nf (map isLetter)
mean: 26.95068 us, lb 26.91681 us, ub 26.99481 us, ci 0.950
std dev: 197.5631 ns, lb 158.9950 ns, ub 239.4986 ns, ci 0.950
I'm curious what the difference is between the functions, and whether
isLetter is ever preferable...
--
Live well,
~wren
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
