Landsburg code

module Main where

--compile as ghc -threaded --make $file.hs -o boygirl
--run as ./boygirl [# of sims] [# of families] +RTS -N[# of CPUS]

import System.Environment(getArgs)
import System.Random(newStdGen,randoms)

main :: IO ()
main = do
  g <- newStdGen
  (c:n:_) <- getArgs
  printResults (read c) (read n) (randoms g)

runSim :: Int -> Int -> [Bool] -> Double -> Double -> (Double, Double)
runSim c n bs gx bx = let (g,b,restbs) = howmany n bs 0 0 in
  if c == 0 then (gx+(avgUp g b),bx+(avgUp b g)) else runSim (c-1) n restbs (gx+(avgUp g b)) (bx+(avgUp b g))

avgUp :: Int -> Int -> Double
avgUp x y = x' / (x'+y') where
  x' = fromIntegral x
  y' = fromIntegral y

printResults c n bs = let (gx,bx) = runSim c n bs 0 0
                          c' = fromIntegral c in
                      do
                      putStrLn $ "Sims: " ++ (show c)
                      putStrLn $ "Avg Girls Fraction: " ++ (show (gx/ c'))
                      putStrLn $ "Avg Boys Fraction: " ++ (show (bx / c'))

howmany :: Int -> [Bool] -> Int -> Int -> (Int,Int,[Bool])
howmany  n rs grrls bois  | n == 0 = (grrls,bois,rs)
                          | (head rs) = howmany n (tail rs) (grrls+1) bois
                          | not (head rs) = howmany (n-1) (tail rs) grrls (bois+1)