Hi Ishii-san, お久しぶりです。 On 2014年11月01日 18:25, Hiromi ISHII wrote:
Since C-Z algorithm is a randomized algorithm, we have to have an access for random number generator when calculating algebraic number arithmetics e.g. writing Num instance for algebraic numbers.
Here is the problem: how to pass-around random number generator throughout pure computaion?
I think one immediate solution is to create global state with `newStdGen` and `unsafePerformIO` like below: <SNIP> But this hack seems rather dirty and unsafe.
Is there any workaround to achieve the same thing?
If it works with the algorithm, you could use a pseudo-random number generator with a fixed seed. For example, here is a program to estimate the value of π (purely) using a Monte Carlo simulation: {-# LANGUAGE BangPatterns #-} module Main where import System.Random (mkStdGen, randomRs) -- | Estamate pi via monte-carlo simulation mcpi :: Int -- ^ number of iterations -> Double -- ^ estimated value of pi mcpi count = step (randomRs (0.0, 1.0) (mkStdGen 1331)) 0 count where step :: [Double] -> Int -> Int -> Double step (x:y:rs) !qrt !i | i < 1 = 4.0 * fromIntegral qrt / fromIntegral count | hit x y = step rs (qrt + 1) (i - 1) | otherwise = step rs qrt (i - 1) step _ _ _ = error "impossible" hit :: Double -> Double -> Bool hit x y = x ^ (2 :: Int) + y ^ (2 :: Int) <= 1.0 main :: IO () main = putStrLn $ "pi ~= " ++ show (mcpi 1000000) Cheers, Travis