Monte Carlo method pi calculation in Haskell

gistfile1.hs

import System.Random.Mersenne( getStdGen, randoms ) 
import Time

data Point = Point { x::Double, y::Double } deriving( Show )

total = 10000000

main = do
  testStart <- getClockTime
  gen <- getStdGen
  rs <- randoms' gen
  print $ pi' rs
  testEnd <- getClockTime
  print $ tdSec' $ diffClockTimes testEnd testStart
  where
    tdSec' td = fromIntegral(tdSec td) 
                + ( fromIntegral(tdPicosec td) / 1000 / 1000 / 1000 / 1000 )

pi' rs = 4.0 * (fromIntegral count) / (fromIntegral total)
  where
    count = length $ filter isInCircle $ points rs

isInCircle pt = sqrt( (x pt)^2 + (y pt)^2 ) < 1

points (x':y':xs) = Point { x=x', y=y' } : points xs
points _ = []

randoms' gen = do
  rs <- randoms gen :: IO [Double]
  return( take (total*2) rs )