fp2/week1/mart/RandomGetallen.icl

   1 implementation module RandomGetallen
   2
   3 import StdEnv, Random
   4
   5 //Start :: *World -> ([Int],*World)
   6 //Start world
   7 //# (rs,world)  = getNewRandomSeed world
   8 //= (shuffle [1..10] rs,world)
   9
  10
  11 Start = shuffle [1..10] nullRandomSeed
  12
  13 random_n :: Int RandomSeed -> ([Int],RandomSeed)
  14 random_n n seed = seqList (repeatn n random) seed
  15
  16 random_inf :: RandomSeed -> [Int]
  17 random_inf seed = iterateSt random seed
  18
  19 iterateSt :: (s -> (a,s)) s -> [a]
  20 iterateSt f s = [a : iterateSt f s`]
  21 where
  22         (a,s`) = f s
  23
  24 shuffle :: [a] RandomSeed -> [a]
  25 shuffle xs seed = (perms xs) !! ((fst (random seed)) rem (fac (length xs)))
  26
  27 fac :: Int -> Int
  28 fac 0 = 1
  29 fac n = n * fac (n-1)
  30
  31 perms :: [a] -> [[a]]
  32 perms [] = [[]]
  33 perms xs = [[xs!!i : xs`] \\ i <- [0..length xs - 1] , xs` <- perms (take i xs ++ drop (i+1) xs)]