-- einfaches Beispiel für Parallelisierung:
-- (Berechnung von Binomialkoeffizienten)
-----------------------------------------
import System(getArgs) -- Argumente lesen

import Parallel        -- Lib. für GpH

main :: IO ()
main = do
        args <- getArgs
	putStrLn ("Binomialkoeffizient "++ args!!0 ++ " ueber " ++ args!!1 ++ ": ")
	let a = (read (args!!0))::Integer
	    b = (read (args!!1))::Integer
            result = binom a b
        putStrLn (show result)

binom :: Integer -> Integer -> Integer
binom n k | k == 0 && n >= 0  = 1
          | n < k  && n >= 0  = 0
	  |(n-k) <= 5         = binom2 n k -- Abbruch (seq. Berechnung)
          | k <= n && k >= 0
               =  let b1 = binom (n-1) k 
                      b2 = binom (n-1) (k-1)
                  in 
        --- parallele Berechnung ---
		   b1 `par` b2 `seq`
                        (b2 + b1)
        ----------------------------
          | otherwise 
               = error "negative Parameter" 
----------------------------------------              
fac :: Integer -> Integer
fac 0 = 1
fac n | n < 0     = error ("Fakultät " ++ (show n) ++ " nicht definiert.")
      | otherwise = n * fac (n-1) --simple               
      
binom2 n k  | k == 0 && n >= 0 = 1
          | n < k  && n >= 0  = 0
          | k <= n && k >= 0 
               =  (fac n) `div` (fac (n-k) * (fac k))   
          | otherwise 
               = error "negative Parameter"