Alex Young wrote:
rand :: IO Int rand = getStdRandom (randomR (0, randMax))
randListTail accum 0 = accum randListTail accum n = randListTail (rand : accum) (n - 1)
randList :: Int -> [IO Int] randList n = randListTail [] n
randPairs :: Int -> [(IO Int, IO Int)] randPairs n = zip (randList n) (randList n)
This looks entirely broken. How about this? randList :: Int -> IO [Int] randList n = mapM (\x -> randomRIO (0, randMax)) [1..n] (Sorry, I'm not very familiar with the Random module. However, I believe this works.) This then gives you an ordinary list of integers, which elides some of the stuff below...
pairIsInside x y = if x*x + y*y < unitRadius then 1 else 0
This is fairly atypical in Haskell. More likely you'd do something like pairIsInside :: (Int,Int) -> Bool pairIsInside x y = x*x + y*y < unitRadius and then later write length . filter pairIsInside instead of using "sum".
doCountPair :: (IO Int, IO Int) -> IO Int doCountPair (a, b) = do x <- a y <- b return (pairIsInside x y)
fSumListTail :: Int -> [(IO Int, IO Int)] -> IO Int fSumListTail total [] = do return total fSumListTail total (x:xs) = do y <- doCountPair x fSumListTail (total+y) xs
fSumList :: [(IO Int, IO Int)] -> IO Int fSumList l = fSumListTail 0 l
Most of this goes away if you use an "IO [Int]" rather than "[IO Int]".
piAsDouble :: Int -> Int -> Double piAsDouble a b = (fromInteger (toInteger a)) / (fromInteger (toInteger b))
I don't *think* you need the toInteger there - I may be wrong...
calculatePi total = do count <- fSumList (randPairs total) return (piAsDouble (4*count) total)
This looks OK.
main = do args <- getArgs (calculatePi (read (args !! 0))) >>= (putStr . show)
This looks OK too - if a little confusing. As a matter of style, I'd write main = do args <- getArgs case args of [size] -> print $ calculatePi $ read size _ -> putStrLn "Usage: CALCPI <size>" But that's just me...