fp2/week1/camil/RandomGetallen.icl

   1 implementation module RandomGetallen
   2
   3 import StdEnv, Random
   4
   5 random_n :: Int RandomSeed -> ([Int],RandomSeed)
   6 random_n 0 seed = ([], seed)
   7 random_n n seed = ([r:rs], s`)
   8 where
   9         (rs,s`) = random_n (n-1) s
  10         (r,s) = random seed
  11
  12 random_inf :: RandomSeed -> [Int]
  13 random_inf s = iterateSt random s
  14
  15 iterateSt :: (s -> (a,s)) s -> [a]
  16 iterateSt f s = [a : iterateSt f s`]
  17 where
  18         (a,s`) = f s
  19
  20 shuffle :: [a] RandomSeed -> [a]
  21 shuffle xs s = (perms xs)!!(fst (random s) rem (factorial (length xs)))
  22
  23 perms :: [a] -> [[a]]
  24 perms [] = [[]]
  25 perms xs = [[xs!!i : xs`] \\ i <- [0..length xs - 1] , xs` <- perms (take i xs ++ drop (i+1) xs)]
  26
  27 factorial :: Int -> Int
  28 factorial 0 = 1
  29 factorial n = n * factorial (n-1)