Don Stewart wrote:
alex: <snip> You can replace most of your loops with Data.List functions, and simplify the code overall by threading around a lazy list of randoms, rather than calling into IO all the time:
import System.Random import System.Environment import Data.List import Control.Monad
randMax = 32767 unitRadius = randMax * randMax
countPair :: (Int, Int) -> Int countPair (x, y) = fromEnum (x*x + y*y < unitRadius)
calculatePi total g = fromIntegral (4*count) / fromIntegral total where count = sum . map countPair . take total $ zip (randomRs (0,randMax) a) I wish I'd known about randomRs a couple of hours ago :-)
(randomRs (0,randMax) b)
(a,b) = split g
main = do [v] <- getArgs g <- newStdGen print $ calculatePi (read v) g
Compiled like so:
$ ghc -O2 A.hs -o A
$ time ./A 100000 3.13548 ./A 100000 0.08s user 0.02s system 98% cpu 0.101 total
We get no stack overflow.
Not with -O2, but: C:\Users\Alex\Documents\HaskellLearning\MonteCarlo>ghc BetterPi.hs C:\Users\Alex\Documents\HaskellLearning\MonteCarlo>main.exe 1000000 Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize' to increase it. But: C:\Users\Alex\Documents\HaskellLearning\MonteCarlo>ghc -O2 BetterPi.hs C:\Users\Alex\Documents\HaskellLearning\MonteCarlo>main.exe 1000000 3.140636 This is a little confusing. Is there a simple explanation for this behaviour, or is it just a matter of "always use -O2 unless there's a reason not to?" Thanks - I really appreciate the explanations. (P.S. Again - sorry for the duplication. I really need to watch my mail client more closely :-) -- Alex