[Haskell-beginners] PI calculation - Newbie question

29 Jan 2010

      Hi Group,

I am just trying to learn the lang and Implemented this PI calculator.
It is really slow and very memory consuming (much much slower than its
equivalent in Clojure for instance)

I think the problem is in  "rs <- sequence (replicate n isRandIn)"  -
But I don't know how to get around it (how do I get a lazy sequence of
rs? Is it the problem anyway?)

-- p.hs simple PI calculator, using the Monte Carlo Method

import System( getArgs )
import System.Random
inCirc :: (Double, Double) -> Int
inCirc (x,y) = if ((dx * dx) + (dy * dy)) < 0.25
                        then 1
                       else 0
               where dx = x - 0.5
                          dy = y - 0.5

randPoint :: IO (Double, Double)
randPoint = do
           x <-getStdRandom (randomR (0, 1 :: Double))
           y <-getStdRandom (randomR (0, 1 :: Double))
           return (x, y)

isRandIn = do
          p <- randPoint
          return (inCirc p)

main  = do
      args <- getArgs
      let n = if null args
              then 10000
              else read $ (head args)::Int

      rs <- sequence (replicate n isRandIn)
      let pi = (fromIntegral(sum rs) / fromIntegral n) * 4
      print pi

[Haskell-beginners] PI calculation - Newbie question

Gabi