1 computePi :: Double -> Double -> Double
 2 computePi n pi  | n <= 0.0 = pi
 3                 | n >  0.0 = computePi (n-1) (pi + ((1/16.0**n)*(
 4                                                                                  4/(8*n+1)
 5                                                                                 -2/(8*n+4)
 6                                                                                 -1/(8*n+5)
 7                                                                                 -1/(8*n+6))))


*Main> computePi 100000 0
8.259320256459906e-3