Hi all, I was curious about how fast the different array implementations were so I decided to test it. I wrote five programs all of which take an array containing 50001 elements, reverse it a couple of times then sum (modulo) them finally printing the sum. The programs are as follows: NormalArray -- uses the standard Array package for everything NormalArrayReplace -- same as NormalArray but builds a new array every time it is reversed UnboxedArray -- uses UArray UnboxedArrayReplace -- obvious IOMutArray -- uses the IOArray from IOExts and everything is in the IO monad I've stuck the code for these at the bottom of this message, but here are the timing results: NormalArray 1.65u 0.20s 0:01.89 97.8% NormalArrayReplace 2.40u 0.08s 0:02.56 96.8% UnboxedArray 0.80u 0.04s 0:00.87 96.5% UnboxedArrayReplace 1.83u 0.07s 0:01.99 95.4% IOMutArray 0.60u 0.03s 0:01.09 57.7% clearly IOMutArray is the best, even outperforming the UnboxedArray. Unfortunately, writing code in the IOMutArray format is much uglier than writing it in the UnboxedArray or NormalArray formats, even though I know that I'm never going to refer to an old version of the array, so inplace updates are a-okay. So my question is: how can I get better performance without wrapping everything in the IO (or some other) monad? - Hal Source code: -- NormalArray: module Main where import Data.Array testArray :: Array Int Int testArray = array (0,50000) [(i, (19*i+23) `mod` 911) | i <- [0..50000]] reverseArray :: Array Int Int -> Array Int Int reverseArray arr = arr // [(50000-i, arr!i) | i <- [0..50000]] sumArrayMod :: Array Int Int -> Int sumArrayMod arr = sumArrayMod' low 0 where sumArrayMod' pos sum | pos > high = sum | otherwise = sumArrayMod' (pos+1) ((sum + arr!pos) `mod` 911) (low,high) = bounds arr main = print $ sumArrayMod $ reverseArray $ reverseArray $ reverseArray $ reverseArray $ reverseArray $ reverseArray testArray -- NormalArrayReplace: module Main where import Data.Array testArray :: Array Int Int testArray = array (0,50000) [(i, (19*i+23) `mod` 911) | i <- [0..50000]] reverseArray :: Array Int Int -> Array Int Int reverseArray arr = array (0,50000) [(50000-i, arr!i) | i <- [0..50000]] sumArrayMod :: Array Int Int -> Int sumArrayMod arr = sumArrayMod' low 0 where sumArrayMod' pos sum | pos > high = sum | otherwise = sumArrayMod' (pos+1) ((sum + arr!pos) `mod` 911) (low,high) = bounds arr main = print $ sumArrayMod $ reverseArray $ reverseArray $ reverseArray $ reverseArray $ reverseArray $ reverseArray testArray -- UnboxedArray: module Main where import Data.Array.IArray import Data.Array.Unboxed testArray :: UArray Int Int testArray = array (0,50000) [(i, (19*i+23) `mod` 911) | i <- [0..50000]] reverseArray :: UArray Int Int -> UArray Int Int reverseArray arr = arr // [(50000-i, arr!i) | i <- [0..50000]] sumArrayMod :: UArray Int Int -> Int sumArrayMod arr = sumArrayMod' low 0 where sumArrayMod' pos sum | pos > high = sum | otherwise = sumArrayMod' (pos+1) ((sum + arr!pos) `mod` 911) (low,high) = bounds arr main = print $ sumArrayMod $ reverseArray $ reverseArray $ reverseArray $ reverseArray $ reverseArray $ reverseArray testArray -- UnboxedArrayReplace module Main where import Data.Array.IArray import Data.Array.Unboxed testArray :: UArray Int Int testArray = array (0,50000) [(i, (19*i+23) `mod` 911) | i <- [0..50000]] reverseArray :: UArray Int Int -> UArray Int Int reverseArray arr = array (0,50000) [(50000-i, arr!i) | i <- [0..50000]] sumArrayMod :: UArray Int Int -> Int sumArrayMod arr = sumArrayMod' low 0 where sumArrayMod' pos sum | pos > high = sum | otherwise = sumArrayMod' (pos+1) ((sum + arr!pos) `mod` 911) (low,high) = bounds arr main = print $ sumArrayMod $ reverseArray $ reverseArray $ reverseArray $ reverseArray $ reverseArray $ reverseArray testArray -- IOMutArray: module Main where import IOExts import Monad testArray :: IO (IOArray Int Int) testArray = newIOArray (0,50000) 0 >>= \arr -> mapM_ (uncurry (writeIOArray arr)) [(i, (19*i+23) `mod` 911) | i <- [0..50000]] >> return arr reverseArray :: IOArray Int Int -> IO () reverseArray arr = mapM_ (\i -> readIOArray arr i >>= \oldi -> readIOArray arr (50000-i) >>= \oldj -> writeIOArray arr i oldj >> writeIOArray arr (50000-i) oldi) [0..25000] sumArrayMod :: IOArray Int Int -> IO Int sumArrayMod arr = foldM (\s p -> readIOArray arr p >>= return . (`mod` 911) . (s+)) 0 [0..50000] main = testArray >>= \a -> reverseArray a >> reverseArray a >> reverseArray a >> reverseArray a >> reverseArray a >> reverseArray a >> sumArrayMod a >>= print -- Hal Daume III "Computer science is no more about computers | hdaume@isi.edu than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume