Changes to Monads/MRand.hs. All files

Monads/MRand.hs

@@ -6,6 +6,7 @@ where  import qualified System.Random as R +-- | A random monad that works with any generator satisfying `RandomGen`. newtype MRand g a = MRand (g -> (a, g))  instance R.RandomGen g => Monad (MRand g) where@@ -14,21 +15,31 @@ instance R.RandomGen g => Monad (MRand g) where                                     MRand m1 = f a                                  in m1 g') +-- | Evaluate an instance of the `MRand` monad with a source of randomness. eval :: R.RandomGen g => MRand g a -> g -> a eval (MRand f) g = fst (f g) +-- | Provides a random value. random :: (R.RandomGen g, R.Random a) => MRand g a random = MRand R.random -randomR :: (R.RandomGen g, R.Random a) => (a, a) -> MRand g a+-- | Provides a random value in a range.+randomR :: (R.RandomGen g, R.Random a)+           => (a, a) -- ^ An inclusive range [lo, hi].+           -> MRand g a randomR r = MRand (R.randomR r) +-- | Provides an infinite list of random values. randoms :: (R.RandomGen g, R.Random a) => MRand g [a] randoms = MRand (\g -> let (g', g'') = R.split g in (R.randoms g', g'')) -randomRs :: (R.RandomGen g, R.Random a) => (a, a) -> MRand g [a]+-- | Provides an infinite list of random values in a range.+randomRs :: (R.RandomGen g, R.Random a)+            => (a, a) -- ^ An inclusive range [lo, hi].+            -> MRand g [a] randomRs r = MRand (\g -> let (g', g'') = R.split g in (R.randomRs r g', g'')) +-- Demonstrates two infinite, independent sources of integers. two :: R.RandomGen g => MRand g ([Int], [Int]) two = do   xs <- randomRs (1, 10)@@ -40,4 +51,3 @@ main = do   let (xs, ys) = eval two g   print $ take 10 xs   print $ take 10 ys-