# Generating π in Haskell

Haskell beats CL quite comfortably using the same algorithm :

Saintly Man? - That Mitchell & Webb Look - BBC Two

module Main( main ) where import System( getArgs ) arccot :: Integer -> Integer -> Integer arccot x unity = arccot' x unity 0 start 1 1 where start = unity `div` x arccot' x unity sum xpower n sign | xpower `div` n == 0 = sum | otherwise = arccot' x unity (sum + sign*term) (xpower `div` (x*x)) (n+2) (-sign) where term = xpower `div` n machin_pi :: Integer -> Integer machin_pi digits = pi' `div` (10 ^ 10) where unity = 10 ^ (digits+10) pi' = 4 * (4 * arccot 5 unity - arccot 239 unity) main :: IO () main = do args <- getArgs putStrLn (show (machin_pi (read (head args) :: Integer)))

The first 10000 digits.

> time ./machin_pi 10000 31415926535897932384626433832795028841971693993751058209749445923078164062862089 ... real 0m0.381s user 0m0.290s sys 0m0.061s

Saintly Man? - That Mitchell & Webb Look - BBC Two