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module Main (main) where
import Data.List (unfoldr, foldl')
import System.Random.SplitMix32
doubles :: SMGen -> [Float]
doubles = unfoldr (Just . nextFloat)
monteCarloPi :: SMGen -> Float
monteCarloPi = (4 *) . calc . foldl' accum (P 0 0) . take 50000000 . pairs . doubles
where
calc (P n m) = fromIntegral n / fromIntegral m
pairs (x : y : xs) = (x, y) : pairs xs
pairs _ = []
accum (P n m) (x, y) | x * x + y * y >= 1 = P n (m + 1)
| otherwise = P (n + 1) (m + 1)
data P = P !Int !Int
main :: IO ()
main = do
pi' <- fmap monteCarloPi newSMGen
print (pi :: Float)
print pi'
print (pi - pi')
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